Guest Series | Dr. Matthew Walker: The Biology of Sleep & Your Unique Sleep Needs｜Huberman Lab

Welcome to the Hubertman Lab guest series where I and an expert guest discuss science and science based tools for everyday life.

I'm Andrew Hubertman and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine.

Today's episode marks the first in our six episode series all about sleep.

Our expert guest for this series is Dr. Matthew Walker, professor of neuroscience and psychology and the director of the Center for Sleep Science at the University of California Berkeley.

He is also the author of the best-selling book Why We Sleep.

During the course of the six episode series for which we release one episode per week starting with this episode one,

we cover essentially all aspects of sleep and provide numerous practical tools to improve your sleep.

For instance, we discuss the biology of sleep including the different sleep stages, as well as why sleep is so important for our mental and physical health.

We also talk about how sleep regulates things like emotionality and learning and neuroplasticity, that is your brain's ability to change in response to experience.

And we discuss the various things that you can do to improve your sleep.

Everything from how to time, lighting, temperature, exercise, eating, and the various things that can impact sleep both positively and negatively such as alcohol, cannabis, and various supplements and drugs that have been shown to improve sleep.

We also talk about naps, dreaming, and the role of dreams, and lucid dreaming, which is when you dream and you are aware that you are dreaming.

In today's episode one, we specifically focus on why sleep is so important and what happens when we do not get enough sleep or enough quality sleep.

We also talk about the various sleep stages, and we also talk about a very specific formula that everyone should know for themselves called QQRT, which is an acronym that stands for quality, quantity,

regularity, and timing of sleep.

For factors which today you'll learn how to identify specifically for you what your optimal QQRT is, and then to apply that in order to get the best possible night sleep, which of course equates to the best possible level of focus and alertness throughout your days.

Both Dr. Walker and I are very excited to share the material in the six episodes series with all of you, and as we march into today's episode one, I'm sure it will both provide a ton of excellent practical learning for all of you, as well as spark many questions that are sure to be answered in the subsequent episodes of this series.

Before we begin, I'd like to emphasize that this podcast is separate from my teaching and research roles at Stanford.

It is however part of my desire and effort to bring zero cost to consumer information about science and science related tools to the general public.

In keeping with that theme, I'd like to thank the sponsors of today's podcast.

Our first sponsor is 8 Sleep.

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Many times on this podcast, we discuss how in order to fall and stay deeply asleep, your body temperature actually needs to drop by about 1 to 3 degrees.

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If you'd like to travel to the other side of the night, I'd like to talk to you about the 8 Sleep mattress that I've been sleeping on.

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8 Sleep currently ships to the USA, Canada, UK, select countries in the EU and Australia.

Again, that's 8 Sleep.com slash Huberman.

Today's episode is also brought to us by BetterHelp.

BetterHelp offers professional therapy with a licensed therapist carried out online.

I've been doing therapy for well over 30 years. Initially, I had to do therapy against my will, but of course I continued to do it voluntarily over time.

Because I really believe that doing regular therapy with a quality therapist is one of the best things that we can do for our mental health.

Indeed, for many people, it's as beneficial as getting regular physical exercise.

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Today's episode is also brought to us by Element.

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As I mentioned before on this podcast, I'm a big fan of salt.

Now, I want to be clear, people who already consume a lot of salt or who have high blood pressure or who happen to consume a lot of processed foods that typically contain salt need to control their salt intake.

However, if you're somebody who eats pretty clean and you're somebody who exercises and you're drinking a lot of water, there's a decent chance that you could benefit from ingesting more electrolytes with your liquids.

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And now for my conversation with Dr. Matthew Walker. Dr. Matt Walker, welcome.

Dr. Huberman, it's an absolute privilege and a delight to be back. That's right. You've been on here before by have during this episode in this series where you're going to go a lot deeper.

By the way, you look very well rested. Thank you very much. I actually slept pretty well last night. I'm just spice it being a foreign location.

Same time zone. That helps just astronomically. Amazing.

Well, rather than ask you what a great night's sleep is for you because I'm pretty sure you're going to tell us that there's some individual differences that people need to pay attention to in terms of what is quote unquote optimal sleep.

Let's start off with the basics. What is sleep?

So sleep, I think in some ways you can define us at least in humans and in fact in all mammalian species is broadly separated into two main types of sleep.

On the one hand, we have something that many people will have heard of called non-repetite movement sleep or non-rem sleep for short.

And non-rem sleep has been further subdivided into four separate stages and they are unimaginatively called stages one through four increasing in their depth of sleep.

So stages three and four, that's the really deep sleep that we can speak about.

And I should explain a little bit at some point what happens during that state within the brain. It's stunning. It's astonishing.

So you've got stages one and two light non-rem sleep when you sort of look at your sleep trackers and it has light non-rem deep non-rem and then ram.

Stage is one and two. Let's light non-rem stages three and four. That's deep non-rem and that's non-rem encapsulated.

On the other hand, we have rapid eye movement sleep or REM sleep and it's named not after the popular Michael Steit band of the 1990s but because of these bizarre horizontal shittling eye movements that occur during the stage of sleep hence the rapid eye movements.

And REM sleep is the depending on your definition and we'll probably come to this in in later episodes.

It's the principle stage in which we dream, but if your definition is quite loose, which is any reported mental activity when I wake you up or when you wake up, then it turns out that we dream in almost every stage of sleep.

But I'll describe REM sleep from here on in as perhaps you dream sleep and I'll make that faux pas.

So you've got these two types of sleep, non-rem and REM sleep.

They will then play out in this beautiful battle for brain domination throughout the night.

And that cerebral war is going to be one and lost on average for the average adult every 90 minutes and then it's going to be replayed every 90 minutes.

And that creates the standard cycling architecture of sleep.

So whoever is listening to this, when your head hits the pillow tonight, what will happen? You'll start to go down into the light stages of non-rem then you'll go down into the deeper stages of non-rem sleep and you'll stay there and after about 45, 50, 60 minutes, you'll start to rise back up again and then you'll pop up and you'll have a short REM sleep period.

And then back down you go again down into non-rem sleep and up into REM sleep. And as I said, you cycle through that on average about 90 minutes, but I'll come back to that.

What's interesting, however, is the ratio of non-rem to REM within your 90 minutes cycle is not stable.

And what I mean is, as you move across the night, the domination of those two types of sleep within the 90 minutes cycle changes such that in the first half of the night, the majority of those 90 minutes cycles are comprised of lots of deep non-rem sleep, but very little REM sleep.

But as we push through to the second half of the night, now that ratio balance, that seesaw balance shifts over and instead we have much more rapid eye movement sleep and very little deep sleep.

So when people think about, okay, I just go to sleep, I lose consciousness, my brain is still. Firstly, nothing further from the truth could be the case in terms of your sleep.

Second, your sleep has a very specific pattern that has consequences to real life.

So let's say that you're someone who normally gives yourself an eight hour sleep opportunity in bed.

But the next morning, based on what I've just told you, you say, okay, well, I want to, I'm going to get a jumpstart on the day or I've got an early morning flight.

So I'm just going to come up with numbers here. I'm not suggesting that this is the ideal sleep schedule by any means, but just to make the numbers simple, let's say someone normally goes to bed at midnight and wakes up at eight.

So there's their eight hour opportunity, but today they're going to wake up at six a.m. rather than eight a.m. to get this push on the day.

How much sleep have they lost? Well, technically they've lost two hours of their eight hour, so they've lost 25%.

But that's not entirely true. They may have lost 25% of their total sleep, but because of the strange structure of deep sleep first and then REM sleep later, they may have lost 60, 70, maybe 80% of their REM sleep.

So I only make this point because understanding how sleep is structured can have consequences.

I will come back to the 90 minutes though. It's fascinating. We've often, and some people will probably have heard this before, it's a 90 minute cycle.

Well, there's huge variability. Some people can have a sleep cycle on average. That's maybe 75 minutes. Others 120 minutes.

Is it consistent with an individual? It is relatively stable within an individual.

So I would say that the size of the difference from one individual to the next is much bigger than the size of the difference within an individual from one night to the next to the next.

Not unlike a healthy menstrual cycle in a woman, which can range from a short as, you know, 24 days to 31 days and still be considered a healthy cycle that's regular.

But, and it will change across the lifespan, of course, but for a good number of years, it's going to be pretty consistent within a given woman.

And yet between women, it can vary quite a bit immensely.

And what's also interesting is that speaking about some sex specific things, there are sex differences.

So on average, man, if you look at them, we'll have a sleep cycle that's about 15 to 20 minutes longer than women, which on a 90 minute average is actually quite a lot.

And I bring this point up because you may have seen some of those claims or devices out there.

Well, firstly, probably on social media and people send me these things and say, is this true?

Which is you really have to strip to your wake up time at these very distinct 90 minute on the clock when the clock strikes the 90 minute midnight, you know, that's when you have to be waking up and you should set your alarm.

Right. These are the rationale. You'll tell me that it's wrong, presumably.

But the rationale of those devices is that one would be better off waking up at the end of a 90 minute cycle as opposed to in the middle of a 90 minute cycle.

Even if it means getting less total sleep, because the argument is that waking up at the end of a 90 minute cycle allows one to be more alert upon waking.

Right. That there's something uniquely special about the completion of a 90 minute cycle that will have you ejected out of sleep feeling like an energizer bunny.

Kind of that's some of the claims that they are not true or false false.

So sleep for as much as you possibly can sleep.

Don't terminate that sleep artificially on the basis of anyone telling you that there is this kind of Da Vinci code magic 90 minutes.

That's unfortunately not true. And I, you know, I've been guilty of saying, you know, it's a 90 minute cycle and repeating that.

So if I didn't know any better, I would believe that so I'm not trying to, you know, just to highs anyone. I'm just simply saying be aware of that and don't worry.

Don't stress about this unique 90 minute cycle. And there's some products out there that say they're going to time you on your 90 minute cycle and wake you up.

I would probably stay a little bit clearer of some of those.

What about going back to sleep? You said to get as much sleep as possible.

If I get six hours of sleep and then wake up and I feel like I could go back to sleep, would I be better off going back to sleep, provided that my work schedule allows for that.

Or is it the case that after you've gotten a certain amount of sleep, that's a good idea to get up and go.

I would say that if you feel as though there's still more sleep in you, there is or

I love that this has become biographical instantly. I was going to be a good episode when that happens.

I would say hold tight, stay in bed with an asterisk that I'll come back to and see if you can get back to sleep.

And we can speak about different ways of helping you do that.

But the reason I put a slight asterisk there is the following.

If you're then in bed for the next 45, 50 minutes, wide awake, the danger and it doesn't happen to everyone,

but the danger is that you start to associate this thing called your bed with this thing called wakefulness and not sleep.

And one of the things that we do in cognitive behavioral therapy for insomnia is we try to prevent you from spending long periods of time awake.

And I would say it's probably about a 25 minute rule of thumb. It's not a rule to rule of thumb.

If after about 25 minutes, you just can't seem to catch it.

And this is happening frequently. I would just be mindful of you then starting to build a bonded association in your brain that your bed is also the place of being awake.

The analogy would be you would never sit at the dinner table waiting to get hungry.

So why would you lie in bed waiting to get sleepy?

And the answer is that you you shouldn't.

And so we need to break that association. Now there's nothing stopping you, however, from saying, there's still sleep in me.

I know that there is. So I'm just going to get out of bed, go to a different room.

I'm just going to read a book, listen to a podcast.

And then only when I feel sleepy, I'm going to go back to bed because my schedule allows for it.

That's the best way I would tell you if you still think the sleep there on the table to try and get it back.

That's immensely valuable knowing that there's sort of a conditioned place effect of being awake in bed.

I must say I get pretty good sleep most of the time.

There've been phases of life, including recently where sleep has been challenging.

And I notice as I head toward the bed to go to sleep recently, the words in my mind are here's the battleground.

Like it's going to be a night of going to sleep waking up, going to sleep waking up.

We'll get to this business of continuity of sleep a little bit later. So we don't have to go into that now.

I should also note, by the way, that for some people when I speak with them, they will.

And it's just because you mentioned it's beautiful.

They will be saying, I'm so surprised because I am watching television and I'm falling asleep on the couch.

And then I get into bed and I'm wide awake and I don't know why.

And that's because in part you've built this connection in your brain.

And when you go into the bedroom, that's what we try to do with cognitive behavioral therapy for insomnia.

You spoke about it as a battleground that it's almost this adversarial thing, which in some ways in first that at that point you feel as though your sleep controls you.

And it is a miserable feeling.

And gradually over time what we would do is work with someone.

And at that point now you control your sleep.

Your sleep doesn't control you.

And that is such a freedom when you get it. But sorry, I interrupted you.

Oh, no, I interrupted you. But thank you.

Yeah, I've prided myself my whole life on being able to sleep anytime, anywhere.

I learned it from my bulldog Costello or maybe that's what brought us together because he certainly had that.

I'm so sure he's not here around anymore with us because I would have loved.

He feels like he is the best sleep ambassador. There's a post-child for good sleep.

Well, he's here in spirit, sleeping.

So this is interesting and I think it's important for people to hear if you can't fall asleep or if you wake up in the middle of the night and you can't fall back asleep pretty quickly after about 20 minutes or so, probably best to get out of bed.

So these 90 minute-ish cycles that include different types of sleep prompt me to ask if you were to describe the basic characteristics of each of those four stages of sleep.

And especially the deeper stages, three and four and REM sleep, not just at the level of rapid eye movements during REM sleep, but in terms of the types of dreams or the characteristics of kind of bodily state.

Maybe you just flesh out the physiology and neurochemistry and touch on kind of the dream features associated with each of these different stages of sleep.

This just gets so exciting to me and even now when I go into the lab where I look at sleep traces from my sleep center, I'm still in awe, in bewildered awe of what the brain does.

So as we start to fall into those lighter stages of sleep, once you get past stage one sleep, which is sort of almost the shadows where you're just wading out,

then you go into stage two sleep and one of the hallmarks of stage two non-REM sleep or something called sleep spindles.

And the way that we measure sleep in a laboratory, by the way, is that we place, you look like a spaghetti monster.

You've got all of these electrodes on your head, you've got things above your eyes and you've got things on your body.

And we're essentially measuring three main signals, electrical brain activity, we're measuring muscle activity and we're measuring eye movement activity.

And I'll explain why those three things are necessary for me to know, are you awake?

Are you in sleep? And if you're in sleep, which stage of sleep you're in?

So going into that stage two non-REM sleep, we've got these sleep spindles.

At that point, I'm looking at the electrical signals from your brain, what we call the EEG or the electroencephalogram.

And these sleep spindles are these beautiful short synchronous bursts of electrical activity.

And they last for about a second to two seconds, maybe a little longer.

And they are bursting at what we call a frequency of somewhere between 12 to 15 hertz.

And what that means is that these brain waves are going up and down 12 to 15 times per second.

That's what our measure is, 12 to 15 hertz.

And then you go back and your brain at that point just started to slow down.

Now, when we're awake, your brain wave activity can be going up and down, maybe 20, 30, 40 times per second.

It's very fast and frenetic. It's actually very chaotic electrical brain activity.

But as we're going into these lighter stages of sleep, then the brain starts to slow down.

And at that point in stage two non-REM, it's maybe going up and down just four to eight times per second.

So a huge deceleration in terms of brain wave activity.

But occasionally you'll get these sort of starts going,

and then you'll get these beautiful bursts of these sleep spindles.

I actually did, I never published it publicly or we did a project called the sonification of sleep.

And we took these electrical signals and then we turned them into sound waves.

And you can actually hear this beautiful sort of, it's almost this beautiful throbbing of a slow down in your brain.

And then you'll hear these spindles almost sounds like that beautiful, delicious rolling R in Hindi.

It's just wonderful.

I'm not sure I can do that. How's it going?

You're getting off to bed. Not too bad. I mean, we're airing on the side of feline, but that's okay.

I'm true.

So, so coming back to, I'm so sorry.

Coming back to sleep, we've gone into light stage two as I'm trying to desperately hold it together.

And we're going down into deeper non-REM sleep.

Now something spectacular happens.

And this is where I just almost lose it every time I see it.

The brain now goes back down and its speed of oscillation of going up and down is maybe just one or two times per second.

It's incredibly slow.

And this is whole brain activity or localized activity.

So we'll come onto this.

At first the way we would measure it is just from these electrodes which are measuring hundreds of thousands of brain cells underneath them.

So a good analogy would be, let's say you're at a football stadium.

And it's stamped for playing Berkeley in American football.

And what we've got is a single microphone dangling over the middle of the stadium.

And that microphone is picking up the summed voices of the 60,000 people underneath.

It's the same thing with when we place an electrode on your head.

You're measuring the summed activity of hundreds of thousands of neurons underneath.

But we've now started to use maybe a hundred, two hundred electrodes on your head.

And we can pick these up in local territories of your brain.

But that beautiful, powerful, slow brain waves that we're getting during deep non-rem stages three and four.

It's not just slow activity.

You would think, okay, that sounds like the brain is dormant.

No, no.

The brain at that point, the size of the waves is almost quadruple, maybe ten X, the size of the brain waves when you are awake.

Why is that meaning that the brain waves are going up and down very slowly?

But the size of them, which is what we call the amplitude, that is now huge.

It's epic.

So think about it.

You're on the beach.

And when you're awake, the waves are coming in very, very quickly, but the small waves.

And they're coming in in a random fashion.

But deep slow wave sleep are these kind of epic things that would happen in Hawaii,

where you just get these 20, 30 foot waves.

And they're coming in very slowly, but they are epicly big.

That is deep slow wave sleep.

And then what happens is riding on top of those big slow waves, all these sleep spindles, they just keep coming.

So according to the sort of the sleep sonification project, what you would hear now, these slow waves would be

shh, shh, shh, shh, shh, shh, shh, shh, shh, shh, shh, shh.

That's the slow wave and the sleep spindle.

What is it that happens in your brain, though, to your question to produce these slow waves?

Well, let's go back to the football stadium analogy.

There before the game, that's wakefulness.

Everyone is having a different conversation and a different part of the stadium.

And you just get this kind of incoherent sort of blabber that's going on.

That's wake.

Your brain is doing different things, different sort of locations of the brain processing,

different information at different moments in time.

And that's the fast frenetic activity of wakefulness.

When you go into deep sleep, all of a sudden, for reasons that we still don't quite understand,

hundreds of thousands of brain cells in your cortex all decide to unite

in their singular voice of firing and they all fire together and they all go silent together.

They all fire together and they all go silent together.

And that's what's producing these huge big powerful waves.

So the analogy in the football stadium would be at this point now

and I'll come across to your university, Stanford is winning.

And the crowd is buoyant and all of a sudden the Stanford crowd is singing,

Berkeley sucks.

And they're all uniting.

The whole stadium cries out at the same time and then goes silent at the same time.

It's an epic display of coordinated neural activity in a way that we don't see

in any other brain state.

It's phenomenal.

It's just in all.

You answered the question I was going to ask which is

does the pattern of brain activity that you just described occur

in similar or identical form during any waking states?

And I think you just said the answer is no.

Meaning if I understand correctly, this is a very, very specialized brain state

unique to sleep, unique to a specific portion of sleep.

And that begs the question, what is it doing?

So it turns out that all of these stages that we'll describe,

different stages of sleep do different things for your brain and your body

at different times of night.

And it's very understandable that people sort of in the public will come over to

me and say, you know, how do I get more deep sleep or how do I get more REM sleep?

And my question back to them first is why do you want more REM sleep?

And they'll say, well, isn't that the good stuff?

And I will say, well, it turns out that they're all important.

You need all of them.

But we can come on to let's I'll speak about non REM sleep functions first.

And then I can probably I should unpack REM sleep and then explain its functions.

But as an overview, what we know is that during deep sleep,

first you switch over in terms of your body's nervous system to what we call

the parasympathetic nervous system that you've spoken about a lot before,

which is this kind of very quiet and calming state of your body's nervous system,

the sympathetic nervous system, which is very poorly named because it's anything,

but sympathetic is very aggravating and activating.

And when we're awake, that seems to be somewhat more dominant,

depending on what state you're in.

But in sleep, especially in deep sleep, you shift over into this very strong

parasympathetic, quiet, and calm state.

And that instigates together with other things.

And we've demonstrated, by the way, that we published a paper probably about a year and a half ago,

that these slow waves and these sleep spindles and the coordination of them,

how well that they're coordinated,

seems to instigate a signal down into your bodies,

what we call the autonomic nervous system, which carries both the sympathetic

and the sympathetic nervous system inside of it,

and forces you over into a parasympathetic state.

So these brain waves, one of the things that they seem to be doing,

is transacting a message to your body's nervous system to say,

calm down, quiet down.

What then happens, firstly, what we see is your cardiovascular system ramps down.

Deep sleep, you could argue, is almost the very best form of blood pressure medication

that you could ever wish for. It's beautiful.

Then something happens within your immune system.

We're starting to unpack this, but we still don't quite know why.

These pulsing deep slow brain waves seem to be a trigger for instigating two things

for your immune system.

Firstly, it stimulates the restocking of the weaponry in your immune arsenal,

so that you wake up the next day and you are a more robust immune individual.

So these are things like T-cells, natural killer cells,

correct?

All of that good stuff.

But what's also interesting, there's a more recent discovery,

it's not just that your body has put back all of this armory in place

and in fact amplified it,

but your body's sensitivity to those immune factors has also increased.

So you've restocked the weaponry and you've made your body more sensitive

to those immune signals.

And that's why we will see in probably later discussions

your immune system can start to become really markedly impaired

when you're not getting enough sleep.

So that's the second benefit of the deep sleep,

brain wave patterns.

The third benefit that we've realised is that it's very good at regulating

your metabolic system and specifically your ability to control your blood sugar

and your blood glucose.

And if we selectively deprive you of just deep sleep alone

and we can do this now very cleverly,

it's not as though I see you going into deep sleep

and I go into your bedroom and I wake you up and then you go back to sleep

and we just how we used to do it sort of ten years ago.

Now we can use a very clever method where we play auditory tones to your brain.

But they are of a level that will not wake you up.

It's what's called a sub awakening threshold and we determine that.

And by playing those tones,

it forces the brain to resurface out of deep sleep.

So you will still sleep a total eight hours.

But I will have selectively excised just your deep sleep.

And when I do that, sure enough,

your blood sugar ability, your ability to control your blood sugar, I should say,

is impaired really quite demonstrably.

And it's for at least two reasons.

The initial thing is that your pancreas,

when it sees this spike in blood sugar,

it normally releases something called insulin.

And that insulin is a trigger to your body to say,

start absorbing the blood sugar so we don't get this toxic

or we don't maintain this toxic spike in blood sugar.

Your pancreas, when you are under-slapped

and specifically when you're not getting enough deep sleep,

does not release the appropriate amount of insulin.

Worse still what we found is that selectively depriving you of deep sleep

means that what little insulin is released,

the cells in your body become less receptive to that insulin.

So you're not releasing enough of this chemical to say,

start absorbing blood sugar.

And the cells that are designed to do the,

they stick a straw out into your bloodstream and they suck up the blood sugar.

They don't respond to the insulin anymore.

So on both sides of the blood sugar regulation equation,

you become impaired.

And then I can give you an example upstairs in the brain.

One of the things that we found and we'll discuss is that

deep sleep helps regulate your learning and your memory functions.

It helps start to move memories around in your brain and protect them

and shift them from short term to long term.

Deep sleep, however, we've now discovered is critical for

de-risking your Alzheimer's trajectory.

It's during deep sleep when you have a cleansing system in the brain

that starts washing away the toxic proteins that build up by way of wakefulness

and two of those toxic components are something that we call beta-emaloid and tau protein

which are fundamental ingredients in the Alzheimer's disease brain equation.

So certainly I could then understand,

based on that litany of things that I've just provided,

and those are only a few of what deep sleep is doing.

You could imagine that's the stuff that I want to get and that's the thing

that I need to optimize for.

Not true because there is REM sleep.

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Before you talk about REM sleep, what about stages one and two of sleep?

Are those just kind of the jog into the sprint that is deep sleep,

stages three and four?

Or if I were to stage the question I'm asking as an experiment,

say I'm an undergraduate or graduate student in your lab and I say,

can we do an experiment where we selectively deprive people of stage one and two sleep only?

And then of course the question becomes, what do you put in there instead?

So there's a bunch of other experiments that we would have to do.

But has that experiment ever been done?

And if so, what is the consequence of being stage one, two deprived,

as opposed to just deep sleep deprived?

So just as you already elegantly demonstrated that stage one selective

deprivation is very difficult because it's a denovo thing you have to pass

through to get to the other stages of sleep.

Is stage one the stage of sleep that I and other people have experienced many times

where you're falling asleep and you start to have a dream perhaps about walking

or running in and then you kick yourself away?

That's right.

And I should have explained what happens to stage one.

I love.

So as we're going into stage one, obviously eyelids are closed.

But one of the first signs that we know as we're recording,

I taught you we're recording the electrical activity on the head with these electrodes.

But I also said that we're measuring eye movement activity.

And as you're going into light stage one on RAM,

for reasons that again, we have no idea why your eyeballs start to roll

in their sockets underneath your eyelids.

That change that we can start to see we call them slow rolling eye movements.

And they are the hallmark of you entering sleep.

And if you are lucky enough to have a partner, you can see this.

You can, you know, as the falling asleep, you will see these bizarre.

Now granted, if they wake up,

usually the relationship is terminated very quickly.

Is the thing?

I mean, someone want to play in the person next to you.

That's probably a factor.

And like, you're a mirror.

Yeah, don't do that.

I'm the only one who gets away with it because I'm a cult carrying sleep scientist.

And even then, yeah, American Airlines sometimes takes some bridge.

But so you get these slow rolling eye movements.

And the brainwaves start to sort of slow down again.

But you mentioned something else.

And they are called hypnogodgic jerks.

And as we're going into this first stage of sleep,

I told you that the principal stage in which we dream is rapid eye movement sleep.

That's not exactly true because everyone has had this experience

that just as you're drifting off, you start to have these little mini dreams,

almost sort of diet or dreams light LIT.

And you can almost wake yourself up

based on the fracture point of cognition.

And what I mean is you're thinking, okay, so tomorrow I've got to get to the studio.

I'm interviewing that desperately annoying British guy, Matt Walker.

And then there was the elephant in the room with the helicopter wings on its head.

And you almost just think it wakes you up because you think,

sorry, excuse me, go back rewind.

What just happened?

That's the point at which you've transitioned over into what we call the hypnogodgic state

where you can have these hypnogodgic dreams.

But you also get these jerks.

We don't fully understand what happens.

But what we do understand is that as you're going into sleep,

you start to lose different aspects of your sensory perceptual apparatus,

not Lewis in the sense of where did I, where did they go?

And I can't find them, but the processing of those.

Now, many will remain during sleep.

One of the things that starts to degrade is what we call proprioception.

And you've spoken about this before, which is knowing how your body is sort of positioned in space.

So it, proprioception is fascinating.

As you're walking with a colleague and you're crossing over a street,

have you ever had that feeling where you sort of you step off the curb and you're chatting and all of a sudden you have one of those really ugly wobbles where you can

low.

And it's because you had calculated non-consciously and computationally,

you understood where your foot was in space.

You understood the velocity force with which it was descending down onto the road below you.

You had miscalculated the distance and your brain had expected your foot to hit that road at a certain time.

And it did not. It sends an aerosignal back up your spinal cord.

And that's where you get that.

This happened to me just last weekend, I was at the San Francisco Zoo.

And periodically throughout the landscape of the San Francisco Zoo, they have these kind of squishy surfaces that are seamless with the concrete around them.

I think this is so kids can play on the various sculptures there.

And if they fall, it's a little bit more forgiving.

So I was just walking across this thing, talking to the person to my left and I stepped on this now rather squishy surface.

And all of a sudden I'm like, well, I don't know how to walk across this thing.

I'm like, you know, I've been walking a long, long period of my life.

And I really had to pay attention.

And then and then transition back onto the concrete and could stop thinking about it for a moment.

And you almost then have to stop the conversation that you are having because it takes over and you switch from non-conscious,

proprioceptive, and you switch over. So the issue is that when you are lying there awake in bed,

you sense the mattress underneath you sense the support, you're getting all of that feedback signal that I was telling you was absent when you

in appropriately calculated the distance down onto the road.

All of that is in place and your brain is saying, everything's fine.

But as we're drifting off into sleep, we start to lose that proprioceptive feedback.

Now normally that loss of proprioceptive feedback and sensation of what's going on and where my body is,

is before the loss of consciousness.

And so you lose consciousness and that's then thereafter when the loss of proprioception happens and you don't have this sort of,

you know, mental freak out of proprioceptive, break glass in case of emergency.

But sometimes the speed with which those things happen changes and you start to lose the proprioceptive sensation before you fully lose consciousness.

And at that point your body says, oh my goodness, mattress is just disappeared and I'm falling.

And that's where you can have these jacks. That's our current best theory.

I know we're going to talk a lot about dreaming in a later episode of this series, but what you just told me,

forces me to ask at this moment, whether or not in dreams where we sense we are flying,

is that possible because of the absence of proprioception.

We're sort of on the mattress or on whatever surface we sleep on, but according to the brain,

there's suspended in space. Is that right?

Yeah, so it's one possibility as to why we have those experiences.

In some ways though it does bring us onto REM sleep.

During REM sleep and I'll explain what happens in the brain, but what you're talking about is something that is even more unique about REM sleep.

As we go into REM sleep, your brain paralyzes your body.

So you are physically locked into the incarceration of your body.

Why would your brain do this? What we call muscle atone now, I was telling you that we measure

your electrical brain activity and we measure your eye movement activity, but we also measure your muscle activity.

Why do we do that? Well, as you're going into non-REM sleep, that muscle tone decreases, but there's still some muscle tone there.

But as you go into REM sleep, in fact, just a few seconds before you enter REM sleep,

I already know you're going into REM sleep because bang, you become completely absent of muscle tone.

And if I were to pick you up, I mean, I'm probably not going to be able to pick you up out of your bed based on certain images I've seen on social media,

I'm going to, if I lived you up, you would just be like a rag doll.

You would have no muscle tone whatsoever.

It's almost like those toys words, like a donkey that sits up and it's got a button underneath and you press the button.

I love them.

It just falls down. I used to have those as a kid to, like the simple things that you and I had as children.

That was basically all the way to the alone one couple of these, but they were, but yeah, I need to get a donkey one in any event.

But sorry, so what you're referring to.

So this, this muscle, and as we call muscle atonia, anything in sort of medicine, usually within A before it means the absence of something.

So sort of if you're, if you have A-rhythmia absence of normal A-rhythmia, aphasia, yeah, sort of, or, and here it's atonia absence of the tone in your muscles.

Why would the brain do this?

Well, the brain paralyzes your body, so your mind can dream safely.

You would imagine how quickly you could be popped out of the gene pool if just like you described, you thought I can fly.

So you get up out of your bed and you go to the window and you launch.

Probably not going to end well depending on what floor you're on.

So this absence of muscle tone, this physical incarceration that we have is one of the things, by the way, that defines REM sleep from when you are awake.

Because if all I was doing in my sleep lab was recording your electrical brain activity, and I was in the other room, and I was just looking at your brain waves, as you go into REM sleep, I would not be able to tell, are you in REM sleep or are you awake?

Why? Because the electrical brain activity is so similar when you are in REM sleep relative to when you're awake.

And what that tells us is that REM sleep is an incredibly active cerebral condition.

Your brain is just firing away. In fact, some parts of your brain can be up to 30% more active when you're in REM sleep than when you're awake.

It's stunning, particularly emotional brain centers. So it's a stunning state of paradox.

And that's the reason that we sometimes call it paradoxical sleep.

Your body is completely immobilized, utterly inactive, but your brain is fervent with its activity.

By the way, people should not worry when I say that your muscles are shut down. And what happens is that just before you go into REM sleep,

there's a bursting activity that will go up into your brain to light up your cortex.

But there's another signal from the brainstem that's sent down all the way down the spinal cord to the alpha motor neurons in the spinal cord that will essentially create this inhibition.

It's only your voluntary skeletal muscles, meaning that your involuntary muscles, things, for example, such as your respiration that helps you breathe in your heart.

That's the reason that we survive and live another day after sleep.

So don't worry about that too much. With two exceptions, though, there are two sets of voluntary muscles.

For reasons that we still don't know either, that are spurred from the paralysis of REM sleep.

One of them is the extra-ocular muscles.

And that's the reason that when you go into REM sleep, you can have these darting horizontal movements back and forth.

They should also have been paralyzed, but they're not.

And then oddly, there is a muscle in the middle-in-ear muscle that does not undergo the paralysis.

And it will also twitch, too, just like your eyes.

But I'm getting into the weeds. So that's what's happening in these different physiological states.

And to your question, when you don't have any muscle tone whatsoever, maybe that is in part the reason why A, you can start to have these dreams of absent gravitational pull, meaning you can start to fly.

It may also be the reason, by the way, that coming back to proprioception, you can sometimes have that feeling of some people will describe my teeth are always falling out.

I always feel as though it's a very common thing, too, or you feel the absence of clothing on your body.

And you say, I walked out and I was going to this meeting and I realized I didn't have any pants on.

And you forget that proprioception is also about knowing that your clothes are on you and sensing those clothes you and I can now direct your attention and sense those clothes on us.

Is it also the case that when we talk about sleep, we talk about falling asleep, that the sense that one is falling back into their head is related to the progressive loss of proprioception in the early stages of sleep?

Yeah, it's just semantics. No, I often think that that may have been where that notion comes from.

We, why would we not say that I am sometimes people say I'm drifting off into sleep, or I'm about to enter sleep and we say I'm falling asleep.

Now, some of that may be that I'm falling into a sort of a deeper and deeper state of a brain wave activity pattern, maybe.

But I actually think you're right now we don't know ultimately the origin of it, but I believe it's in pop because people have this sense of falling hence falling asleep along those lines.

I found that if I sleep horizontally on a bed or sofa, the sleep is far and away different than if I'm falling asleep upright in a chair or partially upright in a recliner.

Yeah, for instance on an airplane now there are a bunch of other things happening on airplanes bright lights noises etc.

So it's not a good experiment to compare those two situations airplane recliner versus in bed at night.

Too many variables, temperatures, especially.

But is there any evidence that one's bodily position during sleep or the orientation of the feet relative to the head, you know the angle elevated or upward or downward.

Has any impact on the pattern of different sleep stages or quality or any other aspects of sleep.

There is a reason for it and we'll probably come on to this at some point when we speak about different methods for sleep optimization or the new wave of fascinating sleep enhancement tools has to do with temperature we think.

That for you to be able to fall asleep and stay asleep you have to drop your brain and body temperature by just a little less than about one degree Celsius or probably two two and a half degrees Fahrenheit.

And that's the reason by the way that you will always find it easier to fall asleep in a room that's too cold than too hot because the room that's too cold is at least taking you in the right temperature direction for good sleep.

Whereas the room that's too hot the opposite.

It turns out that the body's ability to dissipate heat what we call thermal regulation here and thermal regulation in one direction which is the reduction in core body temperature is superior when you are lying down versus when you are inclined versus when you are standing up.

Really and in part it has to do with the distribution of blood throughout certain parts of the brain in the distal versus proximal regions meaning sort of the regions that are close to the core of your body versus the regions that are further away.

But your body's ability if we largely take most item items of clothes off you and then we measure the the core body temperature in the way that we do this.

It's delightful technique it's called a rectal probe and it's neither pleasant necessarily for the installation of the the the experiment to doing it and it's certainly not necessarily for the participant but putting that aside for a second.

They we can measure your core body temperature and we can measure using temperature sensors all over your body.

Exactly what's going on with the blood flow and we can measure how the brain is starting to dissipate the heat because.

One of the principle ways that we dissipate heat from our body is by moving blood around the body when we bring blood into the core of our body we're trapping it in the core and our core body temperature increases when we push that blood out to the surface.

It goes to these thin sort of capillaries and vessels on the surface of your skin and you start to dissipate that heat and you dissipate it more quickly so your core body temperature drops.

And the bodies sort of phasor active capacity for distributing that blood and then releasing that trapped heat from the core of the body is superior when you are lying down and therefore your body temperature can drop more quickly which is one of the many reasons why it's not as easy to fall asleep when you're sort of at a 45 degree angle and why the quality of your sleep won't be as good.

Now there are other reasons to just as you mentioned but coming back to position I would say that there are maybe there's perhaps at least two pieces of evidence that would recommend positional differences or positional changes.

The first is very obvious if you are someone who is snoring and you have certainly if you have untreated sleep apnea which is where you're not just snoring like the but you'll have an absence of breath that's what the word apnea means here's another one with an A in front of it.

So if you know you've heard of pneumonia and it this is about breath and apnea is about an absence of that breath and with sleep apnea not only do you start to have an airway collapsing partially and that's where you get that flutter and that's the sound of the flutter that we're having but then at some point you just hear silence at that point the person stop breathing entirely absence of breath.

That is much more likely to happen if you are sleeping on your back because when you're sleeping on your back your airway is giving way to gravity which is wanting to pull the airway down and close it and shut it off.

So one of the suggestions for people who have snoring or sleep apnea is trying as best you can to train yourself out of sleeping on your back now there's lots of gadgets out there that can sort of help in ways you can do that.

The old school way that we used to do it sleep apnea is more common in men that is in women but women still have it but if you had a male you would bring them into the clinic and you would say could you and it's often males who perhaps are carrying excessive body weight and so there are larger mass size.

You say can you also bring a t-shirt in of your wife and it has to be a t-shirt that is that has a pocket on the front and then we would ask them to wear the t-shirt back to front so it's a very tight fitting t-shirt it's back to front and then you took a tennis ball or a hockey ball in the back pocket and as you're lying there in bed and you turn over onto your back you get this painful signal of your back.

I know is this mat walkers idea this is not me I am not a lover.

I should now be on social media I should be changed to sort of like sleep torture or rather sleep diplomat.

So that's one recommendation just try to stay clear if you're asking me are there certain positions we should stay away from in that circumstance yes it would be.

The other comes back to something I mentioned during deep sleep when this cleansing system starts to kick into gear in your brain and wash away these toxins from the day.

What we've found a little bit of evidence and we in the royal week because I like you my lab doesn't do animal research where we only do human research but some animal researchers had discovered that when animals will sleep with their hair.

Deep with their head on the side that the cleansing capacity of the brain is superior than when the animal is sleeping on its back or sleeping on its front.

And in fact if you look and you would love this project if you go into Google and you just search for sleeping animals look at the head position.

And I will guarantee you that many of them if they're naturalistic are animals with their head turned to the side now the cute ones the funny ones are when you know kitten is split out on its back and it's head is back that's how someone with sleep at me would sort of sleep on their back and.

But that's very rare we almost never see that.

So it's very interesting and what they found was that when those heads were in those sort of side positions the cleansing mechanism of the brain was a little bit better.

It wasn't night or day it's not as though oh my goodness i'm a front sleeper and you know i'm not getting any brain cleansing or am a back sleeper i'm not i'm not saying that there's no need to take it to the extreme.

But i don't think there's any good evidence yet in humans that firstly that's the case and nor is the strong enough evidence to make any recommendations but i just bring it up because it's in the data and it's starting to emerge that if you're to ask me about sleeping position and other any recommendations those the two.

Pieces of descriptive advice i would give you they are not prescriptive pieces of advice mentioned the relationship between temperature and sleep and we're going to get into that in some degree of detail a little bit later because it's so critical but prior to starting to record this episode we were talking a little bit about.

Yawning and you told me something really truly fascinating about yawning which was.

So there are at least four competing theories of yawning that we have and i think there is probably a emerging clear winner.

The first theory was that it was just tiredness that yawning is simply a sign of you being tired and it turns out that that's not true because many people can yawning when they're bored.

And they are not tired and they've been very well rested so that doesn't seem to be true the next one was one that that seems to be very logical which is it's about trying to rebalance your blood gases and specifically oxygen carbon dioxide and you would think that perhaps when you're with that sort of when you're.

And you inhale a huge volume of oxygen what you're trying to do is come back up the oxygen in your bloodstream or when you said and the exhale maybe it's about exhaling more carbon dioxide not unlike the physiological size that occur during sleep of a double inhale with a long exhale correct or that one can voluntarily generate for anxiety management and wake up exactly yeah and so that was a theory that maybe you're trying to balance.

And these these blood gases and there was some very clever experiments where they took individuals and they artificially increased the oxygen levels but more specifically they increased the carbon dioxide levels by direction they tried to manipulate it and they asked did those individuals start to yawning more because the idea would be if your blood oxygen is coming down and your carbon dioxide is starting to rise.

So this theory is correct you should start yawning with greater frequency and there was no difference whatsoever that's probably also the reason that you don't see people yawning on a treadmill or when they're going into more of an oxygen dead and higher levels of carbon dioxide so that theory was knocked out the third theory was one of contagion and it's fascinating yawning like several of the things has a contagious element to it.

So as the audience unexpectedly they didn't know what you're going to say and before you said it you said you told us something interesting about and you did I guarantee you that there will be people listening right now who said I just yawning in response to Andrew human yawning it is very contagious in part it's the mirror in your own system and you obviously understand this in depth your brain has this capacity to mirror.

To mirror the action states of other individuals so good example would be let's say I'm walking out the door now I'm closing the door with my hand and all of a sudden I'm going to get my hand trapped and you on the other side of the room you are seeing my hand and as soon as I trap my hand and I yell out in pain you almost hold your own hand.

Because why why are you doing that it's not just because you know you're trying to be you know compassionate no you have experienced some degree of what I've just experienced how does it do that because your brain has a system inside of it that mirrors my action states and it's called a mirror system and you can imagine why it's very good to understand the action and emotional states of others for

social capacities and all of that good stuff and one of the things that can also happen with this mirror in your own system is that it mimics yawning so when you you might likely hit of yawning increases too because my mirror in your own system is matching your you on and what's interesting is that we know other species also have a mirror in your own system

and that means that when you you on there is a statistically higher chance that your dog will you on and it's cross species so when your dog you on there's a higher probability that you will you on and we've got the station it's it's very clear one of the other interesting theories though is that when species that are cooperative species for example a pride of lions

when one of those lions yawning firstly many of the other lions will you on in a contagious fashion but then consequently there is a collection of actions that happen after that contagious you are and so some people have suggested that the yawning is a way to enact cooperative group behavior that's another theory the final theory number four which I think has the best evidence for

is not the gaseous exchange balancing of carbon dioxide and oxygen but when you inhale oxygen from the outside it's usually cooler than your core body and brain temperature

and when we inhale there is a modest drop in brain temperature and when the brain temperature starts to rise that's when we see yawning frequency beginning to increase

so next time you see someone you don't think of their board or they didn't get enough sleep go over to them hug them and say I know your brain is getting warm it's okay

and then at that point the friendship will be terminated because no one should be hugging each other saying your brain is warm I'm so sorry but anyway that aside I'm sorry I took us down that that tributary of my polluted stream of consciousness

but that's yawning explain those the four theories and we don't have a definitive answer but I think the best one right now that will continue is that it's about brain cooling

that theory makes a lot of sense people tend to yawning when they get tired as you mentioned people can yawning for other reasons as well

if I'm yawning because I'm tired and yawning is to cool off my brain that's too warm is that an attempt to put my brain to sleep because we need to cool the brain in order for it to go to sleep

or something else going on there also and this sort of merges with the previous question about body position

I've lectured in the university for well over a decade as I know you have as well and occasionally every once in a while there's one student I'm just kidding there are several students especially if it's an afternoon class

or a very early morning class that is falling asleep in their chair and then their head they kind of jolt awake and we all know that keeping the room a little bit cooler sometimes helps to keep people awake

as opposed to a warm afternoon classroom but in some ways what we're talking about here violates what you were talking about earlier that it's easier to fall asleep in a cool environment as opposed to a warm environment

the brain needs to cool in order to fall asleep but then when we yawning it's in response to the brain being too warm and so I'm having a little bit of hard time

yeah, yeah, yeah, yeah, please square that circle for me, man, so it turns out that for you to drop your core body temperature the opposite has to happen which is that you have to warm up to cool down to fall asleep

and I mean warm up in a very specific way you have to have the outer surface of your brain warm up you have to get blood to the surface of your skin

and that surface is almost act like a snake charmer that it draws the warm blood from the core and it pushes it to the surface and you radiate the heat out

as you're core body temperature plummets so why would people be falling asleep in an afternoon meeting when it starts to get a little warm?

well in part it's because the warmth of the room is starting to make their face a little bit more rosy

it's drawing the blood out to the surface so what's happening the core of your brain and your body temperature are starting to drop

and at that point that's why you're going to start to feel a little bit more sleepy, that's reason one

the second that you described is that afternoon you're in meetings around a table and you start to get as you said there's wonderful head nuts and people listening

you all know that whether head goes down it snaps back up

it's not that people are listening to good music and sort of doing this head bobbing

it's that they're falling prey to what we know is a genetically hard-wired pre-programmed drop in your afternoon alertness

it's called the post-prandial dip in alertness and that infers that it's after some kind of a meal

it turns out it's not really related to a meal people say well I had a heavy lunch, I had sort of pasture at lunch and I always feel sleepy afterwards

maybe in part but if I remove it I prevent you from having lunch and we've done these studies too

your brain still shows this very reliable drop in alertness somewhere between quite wide but somewhere between about 1 to 4pm in the afternoon

yeah for me it's always between 2 and 3pm which is a time where resisting looking at my watch right now

yeah we might be in that phase of the day I can always feel it and if I close my eyes for 10-20 minutes

I usually can fall asleep pretty quickly for a nap I know we'll talk about naps later

but if I don't and I ride it out I then usually buy about 3-30pm fine

get that rise back up and it sort of swings back up

and so that's in part the reason though explaining the yawning and that warm feeling of I mean the meeting room, the boardroom meeting

and the blinds are open the sun is coming through I've got the sun on my back I'm starting to get very warm

I'm starting to get really really sleepy it's the collusion of two things

it's that you're going into this higher frequency sleep zone in the afternoon

this post-prandial drop in your brain alertness and we can measure it it's very reliable

you can see this dip in your brain hydroactivity and you're getting warm at the surface

which brings blood to the surface releases that heat from the core it drops and boy do you want to fall asleep

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I took us on a bit of a journey into some I don't want to call them side bars

but some specific features around sleep and falling asleep, etc.

let's get back to the different stages of sleep and frame that under the question of

what is great sleep?

what is mediocre sleep? I think we all know what bad sleep is when you can't get sleep

but I think there's a whole different category of bad sleep that you're going to tell us about

which is sleep that we think is good but is actually not as good as we think it is.

I'm always the better doom and gloom.

No, but also the deliver of powerful tools to improve one's sleep

and thereby wakeful state. So along those lines, you know, what is sleep for truly

and what happens when we don't sleep well is perhaps more intuitive to most people.

I feel cranky or I can't remember things or I just kind of you know,

stress seems to feel a little more intense the same amount of stress feels more intense.

And what is great sleep?

And this is I think all under the umbrella of why do we sleep?

I mean, why do we spend a good third to, you know, or more of our life in this incredible state of mind

and body that we call sleep?

And it really is quite stunning state of idiocy when you consider it

because when you're asleep, you're not finding a mate, you're not reproducing,

you're not foraging for food, you're not caring for your young

and worse still, you are vulnerable to predation.

On any one of those grounds, but especially all of them as a collective,

sleep should have been strongly selected against in the course of evolution.

And in fact, one of the founding fathers of sleep research Alan Rekshaffin once said that

if sleep doesn't serve an absolutely vital function, it is the biggest mistake

the evolutionary process has ever made.

And now what we've learned through, you know, almost 10,000 plus research studies

over the past certainly 70, 80 years now is that nature did not make a spectacular

blunder in creating this thing called sleep.

So maybe I can firstly address what is sleep doing and what happens

if we're not getting sufficient sleep.

And then the other question is what is good sleep in terms of what sleep is doing

and why he was right in saying that mother nature didn't make a blunder.

And it hasn't by the way because if you go back every species that we have

carefully studied to date seems to sleep.

And what that tells us even, you know, very old, evolutionary old ancient earthworms

seem to sleep.

They will have a period of what we call the thargicus, which is where they seem to be inactive.

So what I bring that point up because it means that sleep appears to have evolved

with life itself on this planet.

And then it has fought its way through heroically every step along the evolutionary path.

And that by itself must tell us that whatever sleep is doing,

it must be non-negotiably life support necessary.

In what ways is it life support necessary?

Well, we now know many of those.

First, when you're not getting sufficient sleep, I can speak about your hormonal systems.

Let's say I take a group of really healthy young men and I limit them to four or five hours of sleep for five nights.

They will have a level of testosterone, which is similar to someone who is probably ten years older than them.

So a lack of sleep will aid you within five days by a decade.

We also see equivalent impairments in female reproductive health caused by lack of sleep.

Empowerments in estrogen, in follicle stimulating hormone, and also in luteinitin hormone.

And what about the effects of a single night's poor sleep on hormones?

And not to get too down in the details here, but is it necessary to have four or five nights of minimal sleep in a row before you start to see these effects?

Or let's say somebody is getting good sleep for three nights or four nights of the week,

but then the other three are kind of challenging for whatever reason.

But does one see a graded effect, a kind of intermediate reduction in sex-story hormones like testosterone, estrogen, follicles to me?

There is some degree of a dose response curve, but we haven't mapped it out with...

So the way I would want to do it as a sleep scientist would say,

okay, I'm going to do this for one night, and I'm going to thin slice you to seven hours, six hours, five hours.

And then I'm going to do it for two nights, and you're going to again be in the six-hour, seven hours for us.

And I would like to build up this high fidelity map and understand that we don't have that.

But certainly what we know is that a night of total deprivation will markedly impair those hormones.

And we know that after about, you know, a working week of short sleep, you see those impairments too.

But let me come back to you one night.

So that's the hormonal system as an example.

And we've already spoken, or I'll come back to it right now, the metabolic system and another hormone insulin.

What we found is that if I take you again and I limit you on your perfectly normal, healthy, you don't have any signs of type two diabetes,

and I limit you to, let's say, five hours of sleep for four nights.

And then I measure your ability to dispose of blood sugar and...

Your level of blood sugar impairment is so disrupted that at that point your doctor would classify as being prediabetic.

So I could take an individual and within five nights of short sleep, I can move them towards a path that's getting very close to type two diabetes.

And as I said, we've undistand we, a royal we.

Whenever I say we, by the way, it usually means that...

Well, whenever I say I did something, I mean at my center we did something.

And when I say we did something, I mean that they did something.

That's a fair shorthand for attribution.

And so there are, there are bean studies that have really decomposed exactly how that implements in blood sugar happens.

And we mentioned that earlier in this episode.

I can also then move on to, for example, your immune system.

This is a very good demonstration.

Firstly, there's a great study done by Michael Owen and his colleagues at UCLA and he took individuals, healthy individuals, and he limited them to just four hours of sleep for one single night.

And he measured levels of critical anti-cancer fighting immune cells called natural killer cells.

And what he found is that after that one night of just four hours of sleep there was a 70% reduction in natural killer cell activity.

That is a striking state of immune deficiency.

And just to give people a reference point, these natural killer cells were...

Think of them almost like the secret service agents of your immune system.

These natural killer cells, they are very good at identifying dangerous unwanted elements in your body like cancer and going after them and destroying them.

So you wish for a very virile set of these immunoassassins in your body at all times.

And if you're not getting sufficient sleep, that may not necessarily be the case.

We also know that if you are not getting sufficient sleep in the week before you get your flu shot, and this is just another example of how sleep is critical for your immune system.

If you're not getting that sleep in the week before you get your flu shot, you produce less than 50% of the normal antibody response.

Therefore rendering that flu shot largely ineffective in terms of vaccinating you.

We also know that if you're not getting sufficient sleep on average, let's say that you're getting less than six hours of sleep or less on average, you're almost three times more likely to develop the common flu.

And I know that you, at the time of us recording this, you've released some fantastic content about the flu and the rhino virus in particular.

So that's a good demonstration of your immune system.

We also know that it's not just that it's also your cardiovascular system.

That suffers when you're not getting sufficient sleep.

And here again, the data I think is very strong cardiovascular disease writ large, including stroke and heart attack.

And there is one study that I think illustrates this and granted now in terms of the replication, the effect sizes may not be as big, but the study was interesting.

They didn't do something radical, like depriving you of sleep for an entire night, nor did they just limit you to five hours of sleep for, you know, four nights.

There is a global experiment, sleep experiment that has performed on about 1.65 billion people across 70 countries twice a year.

And it's called daylight savings time.

Now in the spring, when we lose an hour of sleep, what they observed in that paper was a 24% relative increase in heart attack risk the following day.

Yet in the autumn, in the fall, when you gain an hour of sleep, there was a 21% reduction in hospital.

So it's bidirectional and by the way, and as I said, that paper, there are some aspects that you can sort of discuss, but it has been replicated.

We see increased rates of hospitalization after that one hour of lost sleep in the spring.

There are higher rates of car accidents on the road after one hour of lost sleep.

We also see higher rates of suicide after one hour of lost sleep during the spring time change.

We even see this great data.

They looked at the sentencing of federal judges in the United States.

And because it's the federal system, the government system, all of those things are cataloged and well documented.

So you have a huge database and they went back.

And what they found is that in the spring, when we all lose that one hour of sleep opportunity, those judges doled out harshest federal sentencing.

In the day after they had lost one hour of sleep, because their emotional and mood states were impaired and will speak about this in a later episode too.

So if you're up for sentencing or please try to avoid that spring time changes as best you can go for the fall date if it's possible.

So that's your cardiovascular system. I could also tell you that it goes all the way down into the cellular and molecular state of your body.

And this, I'm trying to do this to impress the fundamental importance of sleep.

There was a wonderful study done by my colleagues at the University of Surrey back in the UK by, by Dukyandike.

And what they demonstrated was that if you take healthy individuals and everyone is going to act as their own control.

And you limit them to six hours of sleep for one week versus allowing them to sleep at least eight and a half hours or more time in bed.

And then what they did was they measured the change in their gene activity profile relative to when those same individuals, as I said, were getting a full eight hour plus opportunity in bed versus the six hours of limited sleep.

And they found two interesting things. First, sizable and significant 711 genes were distorted in their activity caused by lack of sleep.

By the way, that's relevant. We know that almost one out of every three, maybe even one out of every two, if you look at the data, people that pass you on the street is trying to survive on six hours of sleep or less during the week.

So it's a relevant ecological manipulation.

The second result was that about half of those genes were increased in their activity. The other half would decrease.

Now, those genes that were impaired by way of one week of short sleep were genes associated with the immune system. So once again, you can see this immune deficiency, but now playing out at a genetic level.

Those genes that were increased or what we call overexpressed were genes that were associated with the promotion of tumors, genes that were associated with long term chronic inflammation within the body, and genes that were associated with cellular stress and as a consequence, cardiovascular disease.

And to me, that's the thing that impressed the fact that there is no aspect of your wellness that seems to be able to retreat at the sign of sleep deprivation and get away unscathed.

It's almost like a broken water pipe in your home.

That sleep will leak down into every knock and cranny of your physiology, and it will even tamper with the very DNA nucleic alphabet that spells out your daily health narrative.

So I paint this picture, which seems dire, and I think someone once said to me, look, your Ted talk, which I think was called sleep, sleep is your superpower.

They said that talk should have actually been sleep or else dot dot dot, which is a completely fair thing because I think, you know, very early on as a public figure for sleeper.

I did a terrible job. I was very dictatorial as I disagree.

Well, I was, I think I was very absolutist and I've learned my lesson. I disagree and, and I'm going to interrupt intentionally not to to puff you up just because, but I, I think that it's fair to say, I know it's fair to say that the cautionary notes that you spoke about in those early Ted talks and in your book, why we sleep.

Well, they may have stimulated some anxiety for some people. They absolutely had and have a net positive effect in the sense that they queued people to the importance of this thing called sleep because prior to you doing that or those things, it was the case that it was the sleep when I'm dead mentality.

And as somebody who's pulled many all nighters in his career, many, many, although not these days any longer, I think goodness.

I can tell you that that information was transformative for my behavior and also for people in the arenas of military sports, children, adults.

It is fair to say that we have better parents, better kids, better citizens of every country as a consequence. So I won't allow you.

One of the few things I'll, I, you know, will have a hard line on I won't allow you to malign your contribution.

And the good news is this series is also going to include a lot of discussion about things that one can do, anyone can do to improve their sleep.

So enough for that. I will walk I will stop trying to reject that.

But I would also put in the comments on YouTube whether or not you agree with me or you agree with Matt.

And then, you know, and thanks for agreeing with me.

I would say though that please don't start as you mentioned that getting anxious if you're not finding it easy to fall asleep that listening to me is first.

You're not going to make matters any better. But don't think even if you're in the general public that like I had one bad night of sleep.

Does it mean I'm now going to develop Alzheimer's disease? Absolutely not.

There's, we're not suggesting that we're talking about a model in which, you know, week after week month after month. Yes, I've demonstrated that, you know, after just one night of something of short sleep, you can see measurable impairments.

And we can and I can't, you know, I can't be untruthful about the scientific data.

But it's not as catastrophic as one may think. And as you said in this series, we will also speak and focus a great deal about what can you do to start to try to optimize your sleep.

So thank you for that opportunity. Absolutely.

So lots of things not good for us happen when we don't sleep enough on a consistent basis. Yes. One poor night sleep.

Let's face it. I mean, our species would cease to exist if that were the case because all these parents that have stayed up, you have a, you know, an emergency or the neighbor's dog is barking or you go to an Airbnb where it's too warm and you can't sleep.

But clearly bad things start to happen when we are chronically sleep deprived.

We hear less often about the great things that happen when we get great sleep.

Perhaps we can talk about a few of those. I mean, obviously, many of them are going to be just the inverse of what you just described.

But for instance, learning neuroplasticity, the nervous system's ability to change and response to experience sleep deprivation and pairs learning.

Yes. Yeah.

And a great night's sleep makes it a lot easier to learn. Right.

So what are the data in terms of the relationship between sleep and learning again, something we're going to go into in quite a bit more detail. But can you give us a.

Can you throw us a bone? Yeah. Some of that. Can you incentivize us for getting good sleep, not just through fear, but we heard the sticks.

You know, throw us a carrot.

Yeah. So there are so many wonderful carrots. So when you are sleeping, your brain's capacity and its learning centers are so much more ready to absorb information.

So think about these memory centers in the brain, almost like a dry sponge, if you've been sleeping well. And they are so excited to soak up new information and retain that information.

So firstly, sleep before learning is going to help you acquire an imprint new memories very effectively.

And we've demonstrated that we'll tell you about the studies in an in a later episode. We also know though sleep after learning does something delicious.

It will take those freshly minted memories.

And it will consolidate them into the brain, meaning that it will start to fixate them almost like sort of setting them in concrete into the brain.

And so you are far less likely to lose those memories, which is to say you are far less likely to forget if you've been sleeping after you've learned.

It's not just that though. Sleep does more than simply strengthen those individual memories. Sleep will start to cross link and connect those memories together.

And as a consequence, the next day you will wake up and those that memory back catalog has now been updated with all of the recent information and it's integrated and it's associated.

So you are now able to come up with new creative solutions to issues or problems that you've been facing because you've updated what we call the associative networks in your brain.

And this is the reason that people will describe having had these insights by way of sleep and these problem solving capacities.

And really that's what to me.

A good student is not simply a student who can learn all of the individual wrote facts and then just regurgitate them.

An individual memory is not as sitting as an isolate island is not particularly useful. That's why your laptop isn't well as long as it's not connected to the internet now and open AI.

It's not particularly intelligent.

I mean, it has a storage capacity that is almost more perfect than your brain.

It doesn't make some of the memory sort of mistakes that we do.

The reason it's not as intelligent as we are in part is because it has not integrated the information.

It doesn't link all of the, wouldn't it be wonderful if you woke up one day and you'd installed a program on your computer and your computer just understood how all of the files were interrelated and connected.

And it was saying, OK, you know, you've double clicked on this file. Well, now I'm going to tell you that there is this related information.

You should pull this in here and it would enhance this paragraph that you're working on or it would improve this experimental idea that you're coming.

It doesn't do that, but your brain does that. How does it do that?

In part, it's because sleep is building these associative networks.

So it's not, it's not simply the student who learns the wrote facts.

It's the student who learns the facts and then understands what they mean.

Sleep is not just about learning and it's not just about knowledge.

It's about wisdom, which is knowing what it all means when you fit it together.

And that's one of the other roles of sleep.

So those are some of the beneficial things that sort of the carrots that can come by way of for your learning and memory.

There are so many other carrots though.

We described for your immune system how there is this restoration that happens during deep sleep and it primes that.

But there are other benefits too.

One of the things that we've discovered and we hopefully will get to discuss this in more detail is that sleep provides almost a rebooting of your emotional and your mood states.

And as a consequence, you wake up the next day and you are dressed with a very different set of emotional clothing.

And sleep when you're getting it almost it's like a set of emotional windscreen wipers that it's just cleared those things off and you wake up.

It's the reason that people will tell you, you know, if something is troubling you don't worry just come back tomorrow.

Just give it a night of sleep and you'll probably feel better tomorrow.

That feeling better notion is sleep acting as this emotional bomb that just so this that those jagged edges that we've, you know, be sort of almost like a CD getting scratched if anyone out there knows it's these days.

But you know, these scratches that we get emotional wounds sleep is starting to heal those as well. So those are benefits.

I could also mention some other aspects of your weight control and your weight gain and this is a huge huge effect size sleep moves the needle on almost every aspect of brain and body health.

I think it's very clear at the stage that there is no single tissue or major physiological system in your body and no operation of your mind that isn't wonderfully enhanced by sleep when you get it or demonstrably impaired when you don't get enough.

But when it comes to appetite and regulation of weight gain, this is immense. Firstly, what we know is that when you're getting sufficient sleep, you can create a nice concentration ratio of two appetite regulating hormones called leptin and growling.

And let me go sort of in the reverse to probably give you a better example. Let me say I deprived your sleep. And what we see is that these two hormones that and I joke, you know, they sometimes sound like leptin and growling sound like hobbits from Lord of the Rings, but they're not the real hormones.

And leptin essentially is the signal that tells your brain, OK, you're you're satiated by your food, you're full and you don't want to eat more so hunger and appetite decrease.

Grelling does the opposite when growing increases. Now it's the signal of hunger and you get increasingly unsatisfied despite eating a full meal. If you've got still high levels of growing, you don't feel satisfied with that meal and many people listening may start to say, I have this feeling where I'm just eating and I just don't feel satisfied on some days.

And those days I suspect can be days when you are not sleeping well. And I think everyone has had this feeling of saying, I just didn't sleep well last night. And I just get ravenous.

And I just unleash this unholy hunger and appetite. That's in part because these two hormones. So what happens is that when we're not getting sufficient sleep, leptin, the signal that says, you're satisfied with food stop eating, that is impaired by way of lack of sleep.

If that wasn't bad enough, the hormone, growl in that says, no, you're not satisfied with your food, eat more, that's the signal of hunger, that increases. So it's almost like double jeopardy, you're getting punished twice for the same crime of not sleeping once by way of a drop in leptin stop eating and once by way of growing foot to the floor acceleration I want to start eating.

That's in part why you're going to your waistline can start to expand when you're not getting sufficient sleep. But when you do it, it's a fantastic way of controlling a guarantee if you start to implement better sleep, your ability to regulate your basil levels of appetite and hunger will decline.

But it's not just that you want to eat less or you at least want to eat an appropriate amount for your body mass. It's also what you want to eat.

And what we've discovered is that when you're again not getting sufficient sleep, you start to eat more, yes you do. But you eat more of specific things.

You crave things like these heavy hitting sort of stodgy carbohydrates like bread and pasta and potatoes and pizza and also you crave simple sugars.

And so those foods we know in excess can be what we call obesity genic foods. They are foods that can lead you to a more rapid amount of weight gain.

Whereas when you are getting sufficient sleep, now you're reaching at the food bar for you're saying, watch, actually I think the salad and those healthy nuts and the fruits and those things look quite appetizing today.

Versus when you are under slept, all you want to do is go after the junk food and because you kind of got these munchies, what's interesting is that a recent discovery came back to that notion of the munchies. When I say I got the munchies, people sometimes think of a drug reference they'll say, well, I've been smoking weed.

I always get the munchies. Why is that? Because when you are bringing in cannabis into the body and these cannabinoids, these what we call exogenous cannabinoids, they will increase your appetite.

They will stimulate your appetite. Cannabinoids are appetite stimulating components, but we all have our own version of cannabinoids that we produce inside of our body that you've spoken about before called endocannabinoids.

When you are under slept, the brain releases more endocannabinoids and that's in part why you get the strong impulse. And thus, go when you start sleeping better, you moderate all of these hormones and these chemicals and your appetite is controlled.

When you eat, you feel satisfied with your food, you're not craving more. When you make your food choices, you're making better food choices.

We did a study with brain imaging, where we under slept individuals and we had them see food items inside of a brain scanner. And they had to rate, you know, how much do I desire and how much do I want these items and those items range from very healthy items all the way to unhealthy items.

It's like ice cream and sort of beats all that good stuff and sweets candy as you would say over here. And we looked at their ratings and by the way, we to make this a more ecological because you could say, well, they're going to know what's the healthy choice of the probably just going to be, you know, politically correct and say, oh, I desire the healthy food because the way that we tried to get around that was we said anything that you said was desirable.

When you come outside of the scanner, we've actually got all of these foods and you're going to have to eat them.

So they were making more real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real,

real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real, real

he asked, what are the reasons that people want to try to improve sleep?

You would have thought that we'd have known this decades ago, and it's a relevant question to the point that you're asking, which is about these carrots.

I know that there is still probably some degree of a sleep loss epidemic out there in the world. There is still that sleep machismo mentality that I can sleep when I'm dead.

So how can we try to motivate people? Well, I can do it with the stick and I can do the whole sort of, you know, if it bleeds, it leads and do the doom stay stuff, and that can motivate.

But why don't I try to understand what it would be for most people that would have them try to enact better sleep behaviors?

And they asked all sorts of different options and the two things at the end of the paper when they did all the statistics that stood out, like two sore thumbs.

I want to try to improve my sleep because I want to improve my mood. I want to improve my sleep because I want to improve my body weight.

People know it. They already knew it. We didn't have to show them the data. And so it's just interesting. So I'm just bringing those two things up as carrot examples. There are many others, of course, too.

Terrific examples of carrots for that one can get if they get adequate sleep.

And we'll talk about quality and some other features of sleep that are important in just a moment. But I'm curious, how come when we are sleep deprived? We get bags under our eyes and our skin health shows it like even one day.

You know, if you know someone well and you see them regularly and they walk in and they look particularly well rested.

Yeah. So we, you know, we think they're, you know, bright eyed and bushy tailed, so to speak. But you can often see it in their skin and in their eyes. How glassy their eyes are open their eyes are also the bags under under their eyes.

And of course, folks, never say to somebody you look tired. It's it's the other way to do it is just if they look particularly well rested on a given day. Say you look well rested.

I told you that today. I did. I did. That's right. I would have forgot about that. But now I remember. And it's true. You look very well rested and being the sleep guy and all.

Why do why do we show our lack of sleep in our skin so rapidly? It's almost like a thermometer on on how much sleep somebody got the night before.

It's stunning, isn't it? And you can almost see it. You know, if you have a partner and they come through to the sort of kitchen in the morning and they look at you and because you're so familiar with that face because it's a face that has imprinted on you thousands of times.

You notice subtle changes and you can sometimes sense, you know, they do look tired, but you're absolutely right. You don't say that. You just say, you know, how are you this morning? And is there anything I can do for you? Should I make you a coffee? Maybe you should go back to sleep.

Yeah, yeah. That's the politically correct indirect way of saying boy, do you look tired? Two things on that front. The first it comes back to the immune system that that sort of pale parlor in a face almost that sickly looking skin in pod is because you're already seeing the effects of the immune system.

And it's the same with the bags under the eyes that part of this reboot of the human being, you know, that human beings seem to have what I would describe as a recycle rate. And it seems to be about 16 hours that after about 16 hours of waitfulness.

We need about an eight hour is seven to nine hours is the recommendation don't get hung up on it will speak about exactly that in a second, but it's that seems to be required to reset this whole panoply of health and physiology of of a human being.

One of the things is the immune system and you get this sickly look about individuals and you get the bags under the eyes. So that in part explains it. There was a great study done by a colleague of mine Tina Sondelen and working out in Sweden at the Carolinska.

And this again was one of those studies that I just thought was so genius and it was a two part study. They firstly took individuals and they sleep deprived of for a night or they allowed them to sleep well. In fact, they went through both of those.

And after a full night of sleep or after a night of sleep deprivation, they went into a studio and they had the picture taken they had a portrait shot done under identical lighting conditions. So now for every participant in the study, you've got two headshots one of when they were sleep deprived one when they were sleep rested great now came the second part of the experiment.

They then took all of those kind of head shots and they recruited a new set of participants who acted as an independent set of judges and those judges knew nothing about the experimental conditions and the manipulations that had just happened.

They were simply shown these images and they were asked to rate how attractive does this person look how healthy does this person look and how tired did does this person look and again they knew nothing about what was going on.

Sure enough with very high statistical probability when the head shot that was taken when they were under slept they rated that individual as looking less attractive as looking more sickly in terms of their appearance and also looking more tired.

First they had proven this thing called beauty sleep that you look a more attractive version of you when you are getting sufficient sleep, but they also noticed this sickliness sort of composition to someone's face.

So that's a very long way of explaining the bags under the eyes. I'm sorry I go off in these tensions and you're not attention to it all I asked you answered and and here we are.

Okay so you've been explaining the different dimensions of sleep the underlying physiology some of the psychological and physiological consequences of getting not enough sleep enough sleep etc.

I think a question that everybody is asking themselves is a how much sleep should they get and b what is really great sleep and then of course there are all these other parameters of sleep you know leaving aside you know whether or not one sleeps you know little bit reclined or on their side etc.

How should we think about this activity that you're calling sleep you know how should we break it down what are the variables that we need to think about in terms of being able to ask ourselves how well or poorly we're doing and for lack of a better way to put it to optimize our sleep.

So I think to me the question of what is good sleep at first it seems to be obvious you can come through again to your partner in the morning and they'll say how did you sleep and you have an answer yeah I slept well or I don't think I did sleep well so we all have some subjective sense but science for the most part science and medicine has usually used a singular rubric rubric which I think is reasonable which is quantity of sleep.

So you would hear that okay how much sleep do we need and what would that look like to be good sleep and the answer is to quantitative answer somewhere between seven to nine hours actually I would answer it differently if someone said how much sleep does an average person need I would say about 90 minutes more.

If you would that's the answer you would give that yeah yeah how much sleep do I need and I would say probably about 90 minutes more if you look at the average data but setting 90 90 more if you look at based on the epidemiological studies of how much people actually are getting but that metric of quantity is the way that most of us and I've been you know certainly party to this as well have answered the question is what is enough sleep or what would be a good amount of sleep.

And good amounts of sleep would be somewhat between seven to nine and that's the current recommendation that's the recommendation by many health organizations including here in the US which is the CDC they recommend or they stipulate a minimum of seven hours for the average adult to me however that doesn't capture the true complexity that sleep really is and it is as we've now discussed in the episode a wonderfully complex ballet of the

physiology and so I step back and I really try to think to me what are the main components that would constitute this recipe for good sleep.

And I've conceptualized what I would describe as the four macros of sleep that there are you know we think of diet that we've got three macros fat protein and carbohydrate for me sleep actually has four macros and you can

remember this by the acronym QQ RT and it stands for quantity quality regularity and timing QQ RT quantity quality regularity and timing and maybe I can just go into detail because I'm telling you you know these are the rules for good sleep no

one response to rules they respond to reasons and not rules so let me explain the reasons behind each one of these so quantity we've already spoken about somewhere between seven to nine for the average adult let me move on to quality we measure quality in a variety of different ways the first principle quality measure of sleep is continuity so meaning was your sleep nice and continuous and you didn't wake up many times

or was your sleep fragmented and littered with many awakenings it was punctuated by these these awakenings if it's very highly fragmented that's what we call poor quality of sleep that's low efficiency of sleep so maybe you would be in bed for let's say nine hours

and you still got seven hours of sleep so if all you used was your quantity measure you would say well you still had good sleep you've had seven hours but two of those hours have been spent a week some total so that is very low quality of sleep

and it's what we would call a low score of efficiency so if you're looking at any of your sleep trackers that's probably best captured by sleep efficiency what is sleep efficiency sleep efficiency is simply calculated as of the total amount of time in bed what percent of that time were you asleep so if I was in bed for eight hours and I slept for six hours I would have a sleep efficiency of 75% because two out of the eight hours 25% of that time I was awake

and an efficiency that is 85% or above we typically classify as healthy sleep and we would like to see you there or perhaps a little bit higher if you have a lower sleep efficiency score than that it usually means that you're awake too much of the time and we'll think about that and address that

so that's one measure of the second queue of the QQRT that's quality but there's another measure that we can also use that measure comes back to the deep sleep that we spoke about and particularly the electrical quality of those brain waves so you can have deep sleep and it can be of different qualities electrical qualities you can have deep sleep that is immensely powerful with huge epic waves

where you can have deep sleep that still is classified as deep sleep but it's a little bit more sort of anemic in its quality and you can't really measure that with these sleep trackers we have to use electrodes and then we decompose the electrical brain activity using a fancy equation and that tells us what was the amount of sort of strength of activity what we call electrical power in that deep sleep regimen so that's another measure that we use the most important measure that we use is the most important measure that we use is the most important measure that we use is the most important measure that we use the most important measure that we use the most important measure that we use the most important measure that we use the most important measure that we use the most important measure that we use the most important measure that we use the most important measure that we use the most important measure that we use the most important measure that we use the most important measure that we use the most important measure that we use the most important measure that we use the most important measure that we use the most important measure that we use the most

for quality. Next is regularity. Regularity and actually I should come back to quality for a long time in sleep science we were using quantity as our major metric for predictability meaning I look at your quality and does it predict your learning or your memory I look at your quantity and does it predict your blood sugar regulation I look at your quantity does it predict your immune health I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look at your quantity and I look

at your quantity and does it predict your mortality risk and the answer has been yes that it quantity does predict many of those things that's great. What was interesting is that if you look at the statistic of the predictability of quantity alone it was strong it was significant but it still left a lot of unexplained what we call variance so there must be that there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is some other things in sleep there is

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you can't just get four hours of sleep that is incredibly good quality and get away with it but you also can't be in bed for nine hours or ten hours getting seven hours of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of

sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really

really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep

but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad quality of sleep but it's really bad

when you say same wake up time same to sleep time plus or minus 30 minutes for each of those is that plus or minus 30 minutes getting into bed or we're talking about falling asleep entering that first stage one it's really from the time of lights out so okay I've been in bed and you know I I got into bed at the same time but last night I went to sleep about an hour later and then the night before you know I went to sleep about an hour later and then the night before you know I went to sleep about an hour later and then the night before you know I went to sleep about an hour later and then the night before you know I went to sleep about an hour later and then the night before you know I went to sleep about an hour later and then the night before you know I went to sleep about an hour later and then the night before you know I went to sleep about an hour later and then the night before you know I went to sleep about an hour later and then the night before you know I went to sleep about an hour and then the night before you

know I went to bed and I just turned the lights out and and then you know two nights ago I got into bed again at the same time but then I was kind of online shopping and I started chatting with a friend in a different time so and then it was two and a half hours later before lights out that is what we would classify as irregular sleep and the reason that this this is really being forced on me is important there was a great study that came out maybe I get

this wrong from about five months from the time of filming this ago and it was it used a huge database it's something called the UK bio bank which is a wonderful database and they looked at over 60,000 individuals and they looked they were able to track the sleep from one night to the next to the next to the next so they had some metric of this consistency this regularity and then they split those 60,000 individuals into quartiles and in there's this is the next one and they looked at over 60,000 individuals and they looked at over 60,000 individuals and they looked at over 60,000 individuals and they looked they were able to track the sleep from one night to the next to the next to the next to the next so they had some metric of this consistency this regularity and then they split those 60,000 individuals into quartiles and then they split those 60,000 individuals into quartiles and then they split those 60,000 individuals into quartiles and then they split those 60,000 individuals into quartiles and then they split those 60,000 individuals into quartiles and

they looked at the next statistical model they looked at people who are most regular versus people who are least regular and they tracked them over years what they found and then they looked at their mortality risk how likely was it that those people would pass away during that study interval and they were also able to map what were they dying of if they passed away. So what they found was that those people who are in the top

quartile of being most regular relative to those people who are highly irregular if you had good regular sleep you had a 49% reduced risk of mortality relative to someone who was very irregular of that general all cause mortality risk when you split it apart there was a 35% decrease in cancer mortality risk.

So they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and

they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they were very accurate and they

I think the whole field we knew that regularity I knew that regularity was important I don't think we understood how important and the strength of mortality de-risking if you're regular or increased risk if you're irregular that this metric of R carried in the QQRT equation. So I've started to be much more mindful myself at least and almost over index that.

The final aspect comes on to timing and I should say that we've used this essentially this kind of equation,

this sleep algorithm as it were of QQRT now in a lot of my work in the past at the sleep center in the past four or five years

and it does seem to be a pretty good proxy of covering predictive wise many aspects of your health

that if you use any one of these by themselves, they help they predict things but if you use them as a

collective that seems to be where you explain most of the variants now it's not by far a perfect measure

there are even more nuanced ways that you would want to split it and I want to split it but I would

say that this is a pretty good proxy for the general public and it seems to be in our research a

pretty good proxy for for health and wellness too. The final aspect of the QQRT quantity,

quality, regularity comes on to timing. How is timing different to regularity because regularity is

about getting your sleep at the same correct time. What I mean by timing is your chronotype.

So people may have heard of this phrase are you a morning type, evening type or somewhere in between?

That it turns out is and it's about a third third split across the population maybe a little bit

different. Does it divide up any differently according to male female and here presumably we're not

talking about children or teenagers that's a whole other business and we'll talk about that.

Yeah, so once you are an adult and that because that pattern of your timing of sleep

does change during development very much so despite we can all remember being kids and wanting to

stay up with the grownups and all of a sudden the last thing we remember was seven o'clock comes

around eight o'clock comes around and you think great I'm going to stay up until 10 or 11 with them

and then you wake up the next morning because you were carried to bed because you were lights out.

So setting that aside once you're an adult and you have your stable rhythm in place

there is variability. Now in sleep science we break it down not into three categories but five

extreme morning type, morning type and neutral evening type, extreme evening type.

Could you repeat those again? So extreme morning.

Extreme morning type. So what qualifies as extreme morning type?

So an extreme morning type would someone who would like to say go to bed around 8 p.m.

and they would be waking up and they wake up very easily around 4 4 30 a.m. in the morning

and they're bright as a bunny they are ready to get to the gym and I'm a neutral I just sit right

in the middle so I'm kind of an 11 to 7 30 kind of guy. Maybe we could walk through this so the

extreme morning type is around 8 and they could be they could wake up at let's say 4 4 30 and then

they would be fine. A morning type maybe they would like to go to bed around 9 30 and then they're

waking up closer to sort of 5 36 then you've got a neutral like me and I would like to go to bed

probably around 11 p.m. and wake up around sort of 7 30-ish I try to give myself about an 8 and a half

hour time period in bed and then you get to the the night hours so then you've got the evening type

and then the extreme evening type which finishes out before 5 the evening type maybe they would like

to go to bed like 12 31 and probably wake up around maybe 9 9 30 and then you've got the extreme

evening type and they are not ready for bed until maybe 2 30 3 a.m. and they're waking up you

know middle of the morning. So what's interesting about your chronotype and by the way people

you can if you want to find out your chronotype if you want an actionable suggestion you can just

go online and you can search for something called just type in chronotype M E Q and that stands

for the morning this evening this questioner M E Q just type in chronotype M E Q and you will see

you can fill it out it takes 3 4 minutes series of questions and it will give you back a score

and that will then book it you into these different flavors and sort of say okay

I've tried all of these and yeah okay and I hate to admit it but if I had my preference I would go

to sleep at 8 8 30 and wake up at 4 30 or so well let me ask you this question because rather than

doing the M E Q I there's a single question I normally ask and say okay Andrew I now put you

on a desert island alone you got nothing to wake up for no electricity no responsibilities no

nothing what time do you think your body would like to go to sleep and wake up and I say that specifically

because if I ask you what time would you like to you're still biased in your head by all of the

trappings of society and this terrible bias towards morning types do you think that naturally

that's probably the regimen that you do yeah great question I would go to sleep sometime

between 90 and 120 minutes after sundown yeah okay so that's why I I was going to answer I'm

either an extreme morning type or a morning type I can go to bed around 9 30 wake up at 5 feeling

great okay or go to sleep early 8 8 30 wake up at 4 and really want to get up and ride

you can exercise now that's not the schedule I follow I may start to follow that schedule I've

tried for various portions of my life but typically I end up defaulting to going to sleep a bit

later 10 10 30 waking up around okay 6 6 30 and that's assuming that there are no events in my life

that are disrupting my sleep because then I'm really going to sleep in if I can and a bunch of

things to try and compensate but assuming everything is cool in life and in the room that I sleep

I would say going to sleep at 9 and waking up at yeah about 4 35 and it feels great and in fact I

always thought of it as a bit of an anti-depressant feel I don't concern myself somebody who's depressed

but I can get a little low level malaise if I'm staying up till 11 30 12 and even waking up at 7 I

don't feel quite right and when I go to bed early and wake up early I feel really really good you

do all day long and what's interesting about that is it works both ways so that malaise that you're

speaking about also happens for evening types who are forced to be morning types unsympathetic

no I'm kidding just kidding just kidding I mean society is we are desperately biased towards the

the morning types and we chest eyes and stigmatize evening types as being slothful or lazy that

they just can't get it together why can't you be at the gym you know at 6 a.m. and in the office

by 9 30 what's wrong is or 7 30 what's wrong with you you know I was weaned in academia and the

late Ben Barris who was my postdoc advisor and then later a a colleague that unfortunately he passed

away in 2017 but he used to say I don't do mornings now he was our department chair at the time but

he would just say I don't do mornings but he would come in around 11 a.m. or noon but he would stay

until 3 in the morning and I feel like there's been a cultural shift I feel like 10 years ago if

you were the person who stayed late at the office or the lab you were considered a hard worker

but getting in early at that time it seems was not as rewarded nowadays maybe some things just

changed in my world but I feel like the person who gets in first kind of gets the prize in terms of

the psychological credential yeah there is there is that reward bias that's given it's this notion

you know the early bird catches the worm so I think the we were desperately on kind society is

engineered towards morning types it's engineered against evening types the reason that that's not

fur is that this and I'll come back to timing again and how it works and why it's important and the

fourth ingredient the fourth macro but coming to chronotype the reason it's unfair is that it's not

your fault that your chronotype is largely genetically dictated and we now understand that there

are at least 22 different genes which augment your chronotype which determine your chronotype in

other words it is gifted to you at birth it's hardwired and it is not your fault yet we still have

the stigma and this this I think disgraceful you know not only under appreciation but almost this

kind of rye look evening types are of a certain kind not very favorably viewed so think about it

this way you would never let's think about another trait i color that is you know genetically determined

and you were to look at me and you would say he's got blue eyes you know it's just you kind of lazy

because you've got blue eyes oh you've got green eyes gosh that's wonderful that's well done

congratulations wait a second it's not easy I didn't get the choice it's genetics what's the same

with your chronotype but coming back to wife me I included it in this sort of algorithm of what is

good sleep if I were to take a an extreme morning type and force them to stay awake until midnight

they're going to be incredibly tired they're going to be so tired and they're going to be grumpy

and miserable and they will have no problem falling asleep the problem however is that they're

still going to because of their their natural chronotype which inf which determines your circadian

rhythm so everyone has this 24 hour circadian rhythm as you know you've been a wonderful

proponent of that and done incredible work in this area we all have this 24 hour rhythm and it

looks like a sinusoidal wave it sort of goes up and we as a dienol species what active and awake

during the day and then you get this awesome downswing at night and we're inactive at night and

it steps and repeats just 24 hour cycle everyone has that so what's why doesn't everyone fit the

same chronotype timing model of sleep if we all have a 24 hour clock well what's different is that

were that peak and that trough sit on the 24 hour clock face varies from one individual to the

next and that is what we call chronotype so this comes back to why it's important the morning type

they are in their all they're awesome downswing of the circadian rhythm at midnight and they are

miserable they're desperate for sleep and when you put them into bed at midnight four hours later

than they would otherwise they are gone the problem is their circadian rhythm now starts to climb

back up around 4 30 in the morning and even though they went to bed at midnight they're probably going

to wake up artificially before the eight hour or seven to nine hour completion and they're going

to be short slept on the back end of sleep yeah this happens to me many many times I want to go to bed

around 8 30 or nine but for social or work reasons I stay up until 11 30 or 12 I fall asleep very

easily yeah almost always have fall asleep easily and then 3 34 in the morning I'm awake

and you cannot get it's almost as though you know I tend to do this yoga need your non sleep

deep rest and sometimes I can fall back asleep that way but oftentimes it's a struggle and so I've

been and it's a struggle because of your chronotype and your circadian rhythm which is on its

wonderful piston upswing now apologies for the most sport reference but I obsessed yeah I can't

help myself I'm not a big f1 fan folks just as is Peter at here so anyway the awesome upswing

that you're experiencing for your circadian rhythm prevents you from sleeping in further but

now let's reverse the table let's take the evening type and I put them into bed at 9 p.m. or 10 p.m

when normally they will not be ready for sleep until 1 a.m and they're lying in bed and they are

wide awake and they cannot fall asleep and this is the principal reason that I will get evening

types coming to me and they'll say look I think I've got terrible insomnia I just have and there are

you know you can think about insomnia in lots of different ways but there may be two broad

categories one is that you have sleep onset insomnia I can't fall asleep or the second is I have

sleep maintenance insomnia which is the sort of the thing that you were describing which is

where and you don't have I don't need to have insomnia but I'm just as an example you fall asleep

quickly but you can't stay asleep that's the maintenance insomnia so they will come to me with

the opposite of your concern which is that they say I just cannot fall asleep and I say okay let me

just ask you a few questions and we go through the chronotype questioner and it's very clear that

they are an evening type and you know there's lots of different things that you would want to

exclude to make sure they don't have insomnia and then you can say you actually don't have insomnia

you you're just an evening type and you're going to bed at the wrong moment in time and if you

try to go to bed at midnight you're not going to suffer from the problems that you have and you'll

sleep through later but of course their response is well I need to be in work by you know 8 AM

and I've got an hour commute so I have to be awake at 6.30 so I need to be in bed by 10

so on both of these ends you can see that the morning type who goes to bed too late

falls asleep easily but can't stay asleep the evening type who is forced to go to bed too early

they can't fall asleep but then they stay asleep and when the alarm goes off at 6.30 AM

they don't want to wake up so this is why when you sleep out of synchrony with your chronotype

things do not look good so in those two circumstances let's say that I standardize it

everyone is going to go to bed at 10 pm and wake up at 6 AM and let's say that we've got a

morning type not an extreme morning type who kind of likes to go to bed at 9.45

they are going to sleep very well it's very close to the natural rhythm so and then I get an

extreme evening type who likes to go to bed at 2 am and I have them sleep the same opportunity

amount 8 hours at the very same time well surely they should be identical they're not going to be

it's not that they don't have the same opportunity they do 8 hours it's just that one is placed

at the inappropriate time on the 24 hour clock for the evening type but appropriately for the

morning type and thus the quality of sleep that they each have is very different and that's why

you always need to build into a metric of what is good sleep it's not just about quantity or quality

or getting it regular it's also about where do you place your sleep opportunity window on that

24 hour clock face to align with your chronotype when you fight biology you normally lose and the

way you know you've lost is disease and sickness that's why to me that final T of QQRT is so critical

does that sort of unpack and explain this beautifully yes beautifully and as you were finishing

up there I was thinking that first of all we've heard of chronotypes or many of us have but the

the way you described it is actually extremely clear as to why this almost has to be the case

because if we think about the extreme example of mistimed sleep which is shift work you know it's

being awake at night and sleeping during the day you know essentially nobody has that chronotype

yeah but people force it upon themselves and by the way thank you shift workers we need you

yeah you know if I have an appendicitis at 4 a.m. in the morning I'm very grateful for people who

can help save my life right truckers airline employees and on and on yeah nurses etc parents taking

care of kids in the middle of the night shift work but we know that there are health issues associated

with being nocturnal and sleeping during the day but of course there are a bunch of other variables

like lack of availability of sunlight if you're sleeping during the day and you're and you're awake

at night but I realized there's no reason to think that one can slide their sleep timing around

even by a few hours and still get away with it in other words this notion of chronotypes makes

perfect sense it's just that the shift work is the most extreme example of being out of sync with

your with your chronotype so I'm certainly going to take this chronotype test but I'll tell you

right now if I could get to sleep tonight at 9 and wake up at 4 that would that would feel so good

I'm going to put you in my calm going to do an intervention you are going to be in bed by 9 o'clock

this evening non-negotiable fair enough yeah well so we have QQ RT right quantity quality

regularity and timing how do we know if we're getting enough sleep and you know this is something

that you know you say seven to nine hours I've heard well if you're feeling alert during the day

but perhaps have just a little bit of that post-porendial dip is it I get that right yeah and you're

probably okay but presumably there's some other ways to to gauge whether or not we're getting

enough sleep or not so there are certainly some ways that we do it in science and clinically but

let's let's let those go for a second and just say for people listening what are some very easy

tests I think the first test that I would offer is if you if you're a alarm clock didn't go off

tomorrow morning would you sleep past your alarm clock and if the answer is yes which for many

people it will be then you're not getting enough sleep you know no other species as well by the way

artificially terminates their sleep it's so interesting but we humans will do it we will wrench

ourselves out of sleep now I told you that regularity is key and I do have an alarm clock I usually wake

up close to it or a little bit before it so I do advocate an alarm clock in fact I would argue

that you should have two alarm clocks you should have a to bed alarm clock and to wake alarm clock

you know we only most of us only use an alarm clock in the morning why don't we have it to tell

us when it's time to go to bed so I have both of those so I would say that it's it's good to use

to keep yourself regular but truly if you would sleep past that alarm time then you're probably not

you're not done with sleep your body isn't done with sleep and animals would not it would never do

that and so I think that's the first metric another metric sometimes it's not that's

incredibly specific but have you ever been driving day after day after day and sometimes you think

I don't know if that light was red or green that I just went through inattentive driving man

by your tongue walker by your tongue so that was you may have been that's that's one you know

potential concern in fact one of the ways that we've developed a metric for dose response to

sleep deprivation is using concentration and alertness tests so in other words if there is a

breathalyzer for a lack of sleep doing these concentration focus concentration tests is

they are so sensitive they're so predictive you get people just to focus on the screen and start

to do very basic stimulus response and they can do that for the first minute two with stimulus

response for those that don't know might be three letters pop up on a screen and then you you

pick two keys you you have access to two keys on the keyboard if the if there are two letters that

are similar you press right you write key if there's only one there aren't two or more letters

that are similar you press left key simple simple things yeah very attention to a rule that's

right and you're just doing a lot of different trials of different rules and just becomes monotonous

it's not really very challenging and that perfectly mimics in some ways but we don't do it for two or

three minutes we'll have you do it for ten minutes and my goodness is it mind numbing I mean it's kind

of just but it mimics very well think about you know just even a one hour road trip at 10 o'clock

in the evening and you're on the motorway the freeway all you've got to do is just focus on the

road and the white lines are coming and there's nothing much to do and you've got to attend and

focus not for ten minutes but for 60 minutes when you are under slept one of the dangerous the

big problems with a lack of sleep is that you don't know you are sleep deprived when you are sleep

deprived and we know this because when I'm tracking your performance objectively it's going down

and down and down but when I'm asking you subjectively how do you think you're doing in terms of

your performance you say ah I'm hanging in there so far I'm good so subjectively you think you

find but objectively you're not the analogy would be a drunk driver at the bar you know they've had

seven or eight beers they've had six shots and they pick up the car keys and they say to you look

I'm fine to drive home and your response is no I know that you subjectively think you're fine to

drive but trust me objectively you're not I'll just call you a taxi don't worry it's fine

it's the same way with a lack of sleep so I make this point about going through the traffic lights

because you can have these lapses of attention and these lapses of attention are caused by micro

sleeps micro sleeps happen when the brain just very briefly it's almost like one of those toy ducks

that kind of dips it's built into the water and then sort of comes back up again and dips it

your brain just drops down and has a quick sample of sleep and micro sleep and we can measure it

in your eyelid that your eyelid starts to have what's called a partial closure it just kind of

goes half the way over or it closes fully shut that's a micro sleep even when it's half open

your brain is essentially offline it's in a sleep like state we can measure it and then it comes

back online so I bring that that's a very long way of saying that's the second metric I would

use are you having these absences where you just kind of lapse another is that you mentioned it

before I just don't feel restored and you could say look I I sleep for probably around about

seven and three quarter hours every night but I just don't I don't feel away I don't feel refreshed

at home so can you operate without needing caffeine and have good grace good mood and good cognition

without needing caffeine before 11 a.m. in the morning and if the answer is no you may be self-medicating

your state of insufficient sleep but that metric of saying I sleep seven hours and 45 minutes

that's what my sleep tracker says but I don't feel refreshed that comes to the second q of q q

r t sufficient quantity of sleep my guess is that I would then look at the quality of your sleep

and we'd probably find a deficiency in the quality of your sleep so there are these different sort

of tools that you can use but a good one is do you feel refreshed and restored by your sleep

it's not a guarantee any of these but in order to answer that question do you feel refreshed

and restored by your sleep could we dig just a little bit into some of the contour of the day so

if I get a good night's sleep which for me means going to sleep early waking up early which

tonight we owe it out that's the plan I wake up pretty quickly I'm alert upon wake up maybe

five ten minutes to get out of semi-graggy state but sometimes I'm just I lids open I'm ready to go

is the latency from wake up time to full alertness is that relevant metric the other question is whether

or not the post-parandial dip is a relevant metric we established already that it's natural to feel

a bit of an energetic dip it somewhere in the afternoon I think you said between one and four

p.m. for you something like that for me that's true between the hours of two and three p.m. assuming

all other things equal I just experienced that no matter what but I could imagine some people

are really dragging in the afternoon and they would like to know is that the normal post-parandial

dip or is that a reflection of not getting adequate sleep is there any way that we could just dig

into these two times of day as a as kind of a a measure of evaluating one's duration and quality

of sleep a little bit more beautiful questions I would say that one should not take necessarily

either of those two is your best metric the reason is the wake up component for some people like you

you're waking up and you are good to go pretty much outpegate many people however will experience

something called sleep inertia which is this it's almost this just period of time a bit like a

sleep hangover the first hour I'm gonna have to come back to a car analogy it's like a classic car

engine where you don't just pull out and you can rev it and it's you know it just needs you need

to warm it up gradually bring the the oil temps up and at that point after about an hour you're

up to operating temperature and you're good to go it's the sense of okay I walk through into the

kitchen and sort of your partner maybe looks at the dishes and I say I know darling I know I said I

was gonna wash the dishes I so sorry I forgot but can I just have my cup of coffee and I'll be the

very best version of myself in about an hour can we discuss it then because right now I'm not the

best version of myself that sleep inertia and that is natural for many people now if you are an

evening type and you're waking up early you're going to have a much heavier sleep inertia period

then you would do that is natural to you but I wouldn't necessarily use that as the direct measure

because many people will have sleep inertia and if you do you may get worried if I say oh it's

the very best measure that you're not getting quality of sleep the post-prandial dip as you

mentioned there before even you the the the monumental organism called entry human even you can

fall prey to that and do fall prey to that so that's how I've actually learned to love it

I just love it you know here it comes and I okay that's the my circadian rhythm and we'll talk

more about circadian rhythm in a few minutes but and if I can get 10 to 15 minutes of shut-eye time in

that post-prandial dip then I really love it and you get and when I bounce right out of that

and we'll speak about how we were designed to sleep maybe in in a later episode two and whether

that should be the way human beings are sleeping so I wouldn't necessarily use that I'm all I always

have this post-prandial dip does that mean I should be worried about sleep I would say that if you

have excessive daytime sleepiness throughout the day where you're constantly tired and that is a

term that we use in in sleep medicine is excessive daytime sleepiness or EDS that should be of a concern

I would use a slightly different metric of the same question but at a different time of day

let's think about that circadian rhythm again for most people even if you're a morning type or

evening type by about 11 a.m. by about 11 a.m. midday you're really starting to get to your peak you

know most people are somewhere either side of the peak or around that peak I would say that if you

are feeling groggy and not alert and awake at 11 11 30 depending on your chronotype I would use

that as probably the better metric of my daytime sleepiness but and by the way it's very interesting

that that peak if you look at that circadian peak when you're at your optimal it's both your

optimal for your brain but it's also for your body it's the point at which your core body temperature

starts to peak that's the moment where you have optimal physiology and when you look at world

records that have been broken in the Olympics and you plot them on the basis of time of day you see

this incredible beautiful spike where most people are breaking world records right in that circadian

sweet spot around that midday period why it's because that's the period where human physiology

seems to be at its optimal thermal temperature at least fascinating pressing you read around

right sometime between 11 a.m. and one of one one p.m. yeah yeah depending on what time somebody

goes to sleep and wakes up correct yeah and one time the chronotype isn't that we'll very

put on average yeah because for me it would be by peak alertness and and physical ability

work output yeah is somewhere between 10 a.m. and noon yeah yeah yeah and that fits both with your

brain and my guess is that if we were to get you into the gym and have you go through your routine

and see if we could do that routine once we've got a basal metric set of metrics I will have you do

it at 7 a.m. then have you do it at 9 a.m. then do it at midday then 3 p.m. then 6 p.m. and then 10 p.m.

same workout same human being but there will be definitive periods of time in the day when you

are optimal and my guess is that that optimality of brain is matched by optimality of body such that

your peak performance output and let's say your peak jump height or your peak muscle strength

would be right around those time periods that fit with your own circadian chronotype

rhythmicity so you've been talking about this 24 hour oscillation in sleep wake activity

called the circadian rhythm maybe we can drill a little bit deeper into the circadian rhythm

you know what is it what can shift it if it indeed can shift and I'm especially curious about

forces other than the circadian rhythm that have an impact on sleepiness sleep and wakefulness

so the way we think about it in sleep science and there is some argument that it's maybe even

more complex than this but for the most part there are two main forces to main processes that will

determine when you want to be awake and when you want to be asleep the first of those we've spoken

about which is your circadian rhythm and that circadian rhythm is you have a clock inside of your

brain you have a central 24 hour clock and it's a master clock and that clock as you've spoken

about many times is called the super chiasmatic nucleus we don't have to get hung up on the

statement just think about it as your master 24 hour clock and it beats out this rhythmic sort of

message of activity for us because we're diurnal during the day and then inactivity at night

activity during the day and it just goes up and down up and down every single day that's your

circadian rhythm and that's the super chasmatic the reason I say it's the master clock we've now

learned that there are these circadian rhythm clocks in almost all cells of the body you've got

clocks all over your body in these tiny little clocks but a little bit like Lord of the rings

just like there's one ring to rule them all well there's one clock to rule them all and that is

the central brain clock the super chasmatic nucleus now you can dissociate those different clocks and

you can get them kind of doing some funky things but for the most part it's the central time giver

so you would think that well that's all you need to tell your brain and your body it's time to

sleep or it's time to be awake it's not there is a second force in place here and it is called

process we sometimes call it as process s or sleep pressure so you've got your circadian rhythm on

the one hand going up and down every 24 hours but then you've got this funny thing called sleep

pressure sleep pressure comes down to a chemical that is called a denocene so from the moment that

you and I woke up this morning and everyone listening a chemical has been building up in your brain

that chemical is called a denocene and the more of it that builds up the sleepier and you sleep

ier you will feel and after about 16 or so hours of being awake there is enough of that sleepiness

chemical that a denocene sleep pressure by the way it is a chemical pressure it's not a mechanical

pressure you don't have to worry that your head's going to explode if you go longer than 16 hours

of being awake but that sleep pressure is going to start weighing down on your shoulders and you

you can sense that feeling where you start to think it's you're watching television you you

starting to go down sort of the hill and you think I should go to bed and I'm tired now that's

because of one of two things is happening firstly you're getting to that peak crescendo of a denocene

where it's just getting so powerful that it's knocking you over and you're ready for sleep

usually when you are in synchrony with all of your biology these two forces your circadian rhythm

that goes up and down every 24 hours and your sleep pressure align in this beautiful sort of

Fredrster ginger or just dance partnership and they're in harmony the strange thing is that they

know nothing about each other and they don't care about each other one does not influence the other

they are completely too independent things but let me run it out in the normal circumstance and

then I'll describe to you a good example of how I can separate those two and show you that they're

truly independent so normally when we're in a sort of stable rhythm of sleep wake activity

we're awake during the day we've got this awesome upswing of circadian rhythm and then in the

evening let's just take you for example as you're getting into that sort of eight nine p.m. region

your circadian rhythm has finished its peak many hours ago and it's now starting to descend down

and you're getting onto the steep phase of its downward sort of stroke of its awesome downward movement

but also don't forget that at that moment your sleep pressure your adenosine is also now at its peak

you've been awake for now almost 16 hours so the moment when your circadian rhythm is on it's

nice downward swing and your highest in your levels of adenosine in your steep pressure that's

the moment truly that will determine okay now is when I feel nice and sleepy so then what happens

then you go to sleep you come down that curve of your circadian rhythm and you kind of hit

its nadeer its lowest point in the middle of your sleep phase but also when you go to sleep that

second factor of sleep pressure you are your brain gets the chance to clear away that adenosine

and it seems to be about seven to nine hour period of sleep is enough time for your brain to jatisan

all of that adenosine that has been building up across the 16 hours of prior wakefulness

and then these two things align beautifully again when it comes to your natural wakeup time you've

been asleep for let's say seven and a half hours you've cleared out all of that adenosine so you

no longer have the weight of that sleepiness pushing you down but also your circadian rhythm is now

on its awesome upswing and when those two things align when you dissipated and jatisan all of that

sleep pressure and your circadian rhythm is starting to rise now that's the time when you would

naturally wake up so that's things when they are working well and in alignment let's say that I

now take you and I'm going to deprive you of sleep for 24 hours so now coming into sort of 10 p.m

your circadian rhythm is dropping down and your adenosine is starting to get high and by about

2 a.m you're probably not going to be happy by about 4 a.m or 5 a.m you're miserable why because

you've now been awake let's say for almost 20 hours straight so you've got all of this excess

sleepiness adenosine pushing you down screaming at you've been awake for 20 hours and your circadian

rhythm is at its lowest point desperately wanting to pull you into this thing called sleep and you

feel terrible but then something strange happens by 11 o'clock in the morning relative to let's say

you know for you've now been awake for many more hours still so you've built up even more adenosine

so the prediction would be that if it's just adenosine alone that makes the difference you should

feel even worse at 11 a.m you don't you feel better despite being awake for longer why because

your circadian rhythm has come to the rescue and it's now starting its upswing and it lessons the

distance between those two and you feel a little bit more alert but then as I push through later

into the day by about 6 p.m 7 p.m you're now on your circadian down swing once again and you've

been awake for even longer and at that point there's almost nothing that can keep you awake you're

going to be falling asleep on your feet and your toast but that's a nice demonstration of how you

can separate those two and despite one continuing on you can start to feel better because the other

has come to your rescue and that shows me that your circadian rhythm doesn't care about how much

adenosine is in your brain it's just going to keep going up and down up and down every 24 hours

and your adenosine level doesn't really come much about your circadian rhythm it's going to

just build and build and build the longer and longer that you're awake and then get dissipated

whenever it is that you sleep the clearance of adenosine I'm curious about it how does that work

so this chemical adenosine is building up in our brain does it also build up in the body

it does but in the brain it has this very interesting influence now I've described it as making you

sleepier and it does that's exactly what it does but it does it in a very very interesting way

it's a bi-directional way there are at least two different adenosine receptors or adenosine

welcome sites within the brain and adenosine is very clever in how it makes you sleepy

adenosine as it's rising will turn down the volume on the wake promoting regions of your brain

but yet it will increase the volume on your sleep promoting regions and by way of this dual action

that's how it seems to instigate this feeling of sleepiness by tamping putting the brakes on wakefulness

but hitting the accelerator pedal on sleepiness but then adenosine seems to be part or one of the

reasons that it builds up is because it's a metabolic byproduct of cellular activity of cellular

metabolism and it seems to be that the longer that we're awake because our brain is very

sery-reli active during the day even though I told you that the brain state of sleep is very active it

is it's a very metabolically active state of sleep it is less metabolically active however during

deep non-REM sleep and it seems to be that it's deep non-REM sleep that is the principal time

when we clear we get the chance to clear away adenosine now adenosine clearance is happening

all of the time it's just that the rate of accumulation when we're awake exceeds the speed with

which we can naturally clear but when our brain goes into deep non-REM sleep and becomes less

metabolically active it's not as though there's necessarily a more active or a very proactive state

of deep sleep doing that cleansing it's not it's the same process of adenosine clearance it's just

that there is no longer the accumulation that's happening so it gets the chance to catch up on the

day's adenosine accumulation and then reduce down that adenosine debt and then get you to net net

neutral by the morning and in fact the amount of deep sleep the quality of that deep sleep that

you're getting specifically the electrical quality of your deep sleep is a very good predictor

of how well you dissipate that sleepiness again it's not as though there's something special about

non-REM sleep that is proactively doing the cleansing faster than happens when we're awake it's just

that the rate of accumulation when we're awake is greater than the exceed and exceeds the capacity

of the clearance so it builds up when we go into non-REM less metabolically active it now the

clearance exceeds the buildup and you're able to cleanse that debt I have two more questions the

first is about growth hormone so I was taught that growth hormone is released primarily in sleep

although there are some daytime activities that can promote the release of growth hormone as

well certain forms of exercise maybe some thermal stimuli etc but that the major

event of growth hormone release occurs in sleep is that true it is although there is some

argument that it is is it sleep dependent or is it simply sleep coinciding okay meaning that is it

it's that at the time of day so is it a circadian process where it's just nighttime

nurse means that you release growth hormone or is it nighttime plus sleep that is needed

and it seems to be a mixture of both but it seems to be more sleep dependent than it is night time

dependent and sleep independent I probably should have said before growth hormone critically

important for growth of children during development but also for tissue repair and metabolism

throughout the life span throughout the life span where adults we critically need it right so if

I understand correctly when one goes to sleep growth hormone is released but that there's a circadian

component as well so it's a bit of an and gate as they say right which is that you need this

and that in order to get growth hormone release and the reason I ask this and I'm going to frame

it this way because I think it's going to both clarify what you said and also lead to a practical

step which is about sleep regularity and timing I've heard that the growth hormone

surge is greatest at the beginning of the night of sleep and that if we go to sleep a few hours

later than usual we miss the opportunity to experience the same level of growth hormone release even

if we sleep the same total number of hours right so um yet more incentive for regular sleep timing

yes so you're right it's an and gate so it's night timeness does help but sleep helps

perhaps significantly more meaning that I can have you experience the night time but I can

deprive you of sleep and selectively of deep non-ream sleep and I can markedly impair your growth

growth hormone release but definitely I think tell me if this is correct put differently if

somebody has to work the night shift and they sleep during the day they'll still get it grow

hormone release but not as much growth hormone release where they to have slept at night correct

so we can do it one of two ways so my way is to say I keep you on a diurnal nocturnal sort of

schedule where you're awake during the day and use a sleep at night but I'm going to selectively

deprive you of just your deep sleep at night so you're still sleeping and you're still spending

the night timeness in bed which is not the shift work version but I can block or not block I can

reduce significantly reduce your growth hormone because I selectively deprive you of sleep or I can

do the opposite which is the shift work approach which is I'm not going to deprive you of sleep you're

going to sleep during the day but now I have held sleep constant so in my version I have held

night timeness constant and I've manipulated sleep in your version the shift worker we've done the

opposite we've held sleep constant the sleeping during the day but we've manipulated night timeness

and now as you said yes they will release some growth hormone even though that's not the natural

time on the 24 hour clock when we would see growth hormone released why because they are getting

sleep because it's a somewhat sleep dependent process but they're not going to necessarily

release as much in part because they're not experiencing sleep at night time phases so you can

you can elegantly separate those two out and that's why it's not quite one or the other but it

seems to be both certainly it's a sleep sensitive I would say sleep sensitive is a very good way

of describing it okay so translated to actionable protocol everyone should strive to get

sleep ideally at night of sufficient quality and quantity which you already discussed and getting

sufficient amounts of deep sleep is going to be especially important for sake of growth hormone

release correct got it my last question has to do with the other end of the sleep cycle which is

toward morning and waking which is the hormone cortisol we hear so often these days about cortisol

and people often frame it as bad cortisol is bad yeah you hear this that is simply not true

record of cortisol from an organism they don't they will not do well right and pretty cool we need

cortisol for immune system function for waking for certain forms of memory formation although too

much cortisol is a bad thing indeed not enough cortisol is an equally bad thing indeed so what is the

relationship between cortisol and emerging from sleep and put differently what is the relationship

between deep sleep and cortisol meaning is sleep one way that we keep cortisol at bay during

stages of the 24 hour cycle when it would be deleterious to have elevated cortisol yes it is

and that's one of I spoke about and we'll come on to this perhaps and when we speak about

emotional and mental health and when we are under slept we shift over into a more sort of activated

sympathetic you know agitated state of our nervous system that's that's one aspect of it but

there's another aspect of the stress response which is yes you get elevated heart rate you're more

sympathetic which is this activated state rather than parasympathetic but you also get when

your sleep deprived a greater release of the stress hormonal axis which is called the HPA axis

which we really want to go to detail it's the hyper with the lamo patuetry adrenal axis which is

a fancy way of saying that it's a signal from your brain going down to release cortisol so when you

go into deep sleep not only do you shift over into the nice quiet rested quiet and state of the

nervous system but you also get a dissipation in that stress related axis and the release of cortisol

cortisol however seems to be also under the strict control of your circadian rhythm where it drops

down at night and in fact you have one of the the steepest declines right at the moment when you're

starting to get sleepy too almost as though your brain and your body know we can't have cortisol

even at sort of normative levels that you would have during the day because otherwise this person

is just going to still be a little bit too wired this is the problem with a stressful event after

say 8 pm at night if you see you see something stressful experience something stressful I mean that

if it's stressful enough will spike your cortisol at that late hour can really impede your entire

sleep structure it's a I would say it's one of the things that I would advocate in terms of

a good sleep optimized routine and we can come onto that and avoiding stress and arguments and

disturbing news and things like that as much as it is possible yeah in the late evening and early

night hours even if you don't think you're necessarily someone who's sensitive to that night

turns out I am someone who's sensitive to that it can really quite trigger me so I stay away from

it we often see this within some near two and we call it the tired but wired phenomenon and people

will say to me look I am just so tired I am so so tired but I'm just so wired that I can't

fall asleep I'm desperate for sleep I know I want sleep but I can't fall asleep because I'm just

so wired and that is a sympathetic hyper cortisol state and we you can see it in their physiology

but coming back to your question cortisol will drop naturally throughout the night but then it starts

to rise back up and will start to produce its fantastic sort of peak climbing rate right at the

moment when you would naturally again want to wake up so what we're mapping here is this wonderful

tapestry this kaleidoscope of coordinated biology that your adenosine levels are finally coming to

their lowest point your circadian rhythm is starting to rise your cortisol levels are starting to rise

your core body temperature is starting to increase because it's dropped throughout the night

all of these things unite in this beneficial timing ballet of just brilliance that naturally has

you waking up and feeling like you're ready to go if everything is aligned if you've got your

chronotype right your sleep quantity your quality regularity and you're sleeping you know in

appropriate sort of timed amounts well your enchantment with sleep is indeed infectious

I've experienced it and I know that everyone listening and watching has experienced it as well

as you've taken us through this truly spectacular voyage through this phenomenon that we call sleep

when you informed us about what sleep is what the different sleep cycles are how they are structured

and interrelated we talked to us about the four macro nutrients of good sleep quantity quality

regularity and timing highly actionable information and then of course some of the hormonal

neurochemical interactions and consequences of good sleep bad sleep for mental health physical

health and performance so first I'd like to just extend a giant thank you for taking us on this

voyage in this first of several or more episodes of this mini series on sleep and I very much

look forward to our discussion in the next episode about how to improve one's sleep and perhaps even

optimize one's sleep so thank you maps ever so much on behalf of myself and listening audience

can't wait to continue the discussion further can't wait thank you again for having me in this

opportunity what you do for the public by the way in terms of your advocacy for science and also for

health for what you do thank you and forgiving me this opportunity to be here to share the message

of sleep thank you thank you so much for the kind words it's a labor of love and it's a delight to

be able to join arms and educating with you thank you thank you for joining me for today's episode

with Dr. Matthew Walker to learn more about Dr. Walker's research and to learn more about his

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[睡眠科學：揭秘睡眠結構、重要性與最佳化策略（第一部分）]-[Guest Series | Dr. Matthew Walker: The Biology of Sleep & Your Unique Sleep Needs]

📋 Summary

導言

睡眠的生物學架構

睡眠的重要性與剝奪的後果

睡眠優化：QQRT 公式

腺苷與晝夜節律的運作機制

結論與實踐建議

🎯Key Sentences

📝Key Phrases

📖 Transcript