Matthew Walker [ 12 JUN 2019 | Sleep Engineering | 56:55 ] The number of people who can survive on seven hours of sleep without showing any impairment, rounded to a whole number and expressed as a percent of the population, is zero.

MATT BRITTIN: OK. So hopefully, you’ll give some guidance and some case to change to all of us.


MATT BRITTIN: Don’t despair.

MATTHEW WALKER: There’s hope on the way. Trust me.

MATT BRITTIN: Yeah, well, I think what I’d like to do is start with just the basic question. What is enough sleep? And what goes wrong when we don’t have enough sleep?

MATTHEW WALKER: So right now, we recommend somewhere between seven to nine hours of sleep. The sweet spot is probably about eight for most human adults. How do you know if you’re not getting enough sleep is one of those questions. Several things– firstly, if you are setting an alarm– by the way, I’m going to probably just look at you, Matt. Because I know there’s this strange thing that happens with an audience where you’re sort of I’m not.

MATT BRITTIN: You can try, but you may want to divert your attention.

MATTHEW WALKER: I will just speak to you. But one of the things is if you set an alarm and the alarm didn’t go off, would you sleep past your alarm? And if the answer is yes, then you’re not done with sleep yet.


MATTHEW WALKER: And in fact, when we’ve studied hunter/gatherer tribes whose way of life hasn’t changed in thousands of years and you speak about this sort of artificial termination of sleep, they’re utterly puzzled. Why would you stop something that hasn’t yet completed? What’s also fascinating, by the way, is that if you ask them about sleep difficulties, here in most developed nations, the insomnia rate is about 10% to 15%. There, based on our estimates, it’s about 1% to 2%. They just don’t understand the concept of not being able to sleep. So there’s something about modernity that’s desperately dislocated us from this thing called a good night of sleep.

MATT BRITTIN: Right. And so let’s just talk for a minute. So a lot of what you cover in the book and that you’ve covered in your research is the health issues that arise from lack of sleep. So just tell us. Let’s start with the worst, right? So what happens to you cognitively, fitness-wise, illness-wise, attractiveness-wise. What are the things that happen?

MATTHEW WALKER: Let me start with attractiveness. So we’ve all heard of this thing called beauty sleep. It’s this old tale that you would get– well, it’s actually true. And there was a wonderful study done in Sweden. And they took a group of healthy young individuals, and they gave them a full night of sleep. And then they deprived them a night of sleep. So they went through the experiment twice. And at the end of each one of those, after a good night of sleep or being sleep deprived, they took a portrait shot. And then came the second part of the experiment, which was, essentially, a beauty contest, where they took independent judges who knew nothing about the two experimental conditions, and they just said, rate these pictures on the basis of how attractive, how healthy people look, how sickly they look, how tired or sleepy they look. And even though these judges knew nothing about the experimental conditions, they routinely rated you when you were shot under conditions of being sleep deprived as being less attractive, looking more sickly, and looking a lot more tired.

MATT BRITTIN: That’s after one night.

MATTHEW WALKER: After one night. So there is objectively a thing called beauty sleep. And people independently can see it, which is no surprise. Because people will come in all of the time, and they’ll sometimes say to you, if they’re honest, they’ll say, wow, you know, you look tired. How do you know that? Because it turns out that there are–

MATT BRITTIN: You can read people really well.

MATTHEW WALKER: –clear facial cues and bodily cues that express this thing called insufficient sleep. And other human beings can pick up on it.

MATT BRITTIN: Right. So thing one– you get less attractive. There are other things, though, too. What happens to you cognitively? What happens to your capability to make decisions, to learn, to do all the stuff we have to do in a working environment?

MATTHEW WALKER: So if you’re not sleeping, one of the first things that you become deficient in is your capacity to learn. So we’ve done studies where we’ll, again, deprive people of sleep or give them a full night, and then we’ll try and have them learn a whole list of new facts. So essentially, is pulling the all-nighter a good idea? And the answer seems to be no. Because the brain is about 40% deficient in its ability to lay down new memory traces | it is underslept. And 40% is non-trivial. That’s the difference between acing an exam and failing it miserably. And I think that’s particularly concerning for sleep in our education populations right now. We also know that you need sleep after learning, however, not just before learning, to essentially hit the Save button on those new memories so that you don’t forget. One of the other things that starts to go awry is your emotional stability. What we found is that there’s a deep structure in the brain called the amygdala. And it’s the centerpiece region for the generation of strong emotional reactions, impulsive reactions. The reason that you typically are not impulsive and you’re emotionally rational is because another part of your brain called the prefrontal cortex, which sits above your eyes, that’s like the CEO of the brain. It’s very good at making high-level, top-down, controlling decisions. And it keeps our emotional brain in check. But when you’re sleep deprived, the first part of the brain to take a nosedive like a dart into the ground is your prefrontal cortex, which unleashes your emotional brain. And so we see that the amygdala is about 60% more reactive under conditions of sleep deprivation. And what’s interesting is that it’s pendulum-like, that you are not only more negative in terms of your responses, you’re also much more likely to be more reward-seeking and more sensation-seeking. So the emotional distance within which you travel when you are sleep deprived is vastly larger. So you become more emotionally irrational, as well upstairs in the brain. The other thing I would note, by the way, that’s increasingly now interesting within the brain is not an acute effect but a chronic effect. That chronic effect concerns Alzheimer’s disease. And we now know that insufficient sleep is probably one of the most significant lifestyle factors determining whether you will develop Alzheimer’s. Why is that? The reason is because at night, there is a cleansing system that kicks into high gear within your brain. So in your body, you have a cleaning system called the lymphatic system. Well, in your brain, we recently discovered that you have something called the glymphatic system because it’s made out of these cells called glial cells. And at night, it’s during deep sleep when that cleansing system kicks into high gear, and it washes away all of the toxic metabolic byproducts that build up during the day. Because wakefulness is low-level brain damage. One of the sticky toxic proteins that it washes away at night is a protein called beta amyloid. And if you deprive rats of sleep, they immediately start to escalate the amount of this Alzheimer’s protein in their brain after just one night. We’ve now done the same experiments in humans, and you can see that causal trigger after just one night.

MATT BRITTIN: And this is like taking the plaque out of the brain, effectively.

MATTHEW WALKER: Exactly. So it’s essentially good night’s sleep clean, in that sort of sense.

MATT BRITTIN: And I read– so I was going to ask you about this– I read that you got into this whole area way back when you were actually looking at Alzheimer’s and trying to understand why Alzheimer’s seemed to lead people to sleep less. But actually, you realized that it was the other way around, that it was sleeping less that was contributing to the Alzheimer’s. Is that how it worked out?

MATTHEW WALKER: Yeah. So I think we’re all accidental sleep researchers in the field. No one, when they’re a child and you go around the classroom, and the say, what would you like to be when you grow up, no one says, I’d love to be a sleep researcher. And I fell into it by accident. During my PhD, I was trying to use brainwave patterns to diagnose people with different types of dementia very early on. And I was failing miserably for the first couple of years. And I used to go home. And I have this little igloo of journals in my room. And I’d read them at the weekend. And then, one weekend, I realized, reading an article, that, in some dementias, like Alzheimer’s, the centers that generate sleep are those that are attacked by the disease, whereas in other types of dementia, like vascular dementia, you typically don’t have that. So I thought, well, maybe I’m measuring my patients at the wrong point in time– when they’re awake. I should be measuring them whilst they’re asleep. Started measuring their sleep, got some great results. And at that point, I then said, if sleep is so disrupted in these Alzheimer’s patients, is it not just simply a symptom of the disease? Could it actually be a causal trigger of the disorder? And now, 20 years later, that’s exactly what we’re finding.

MATT BRITTIN: And that’s what you’re working on, or some of the things you’re working on, in your Center for Sleep Science?

MATTHEW WALKER: Yeah. So we do a huge amount of work with aging and Alzheimer’s disease. We know that a psychological signature of aging is that our memory gets worse. But a physiological signature of aging is that our sleep gets worse. And only recently we published evidence that those two things are not simply co-occurring. They are significantly interrelated. And what’s exciting– or that may sound very depressing, that it’s in the mail. It’s coming at you. It’s non-negotiable. But unlike many of the other factors that are associated with brain aging– for example, changes in the physical structure of the brain or even the vasculature of the brain– those are fiendishly difficult to treat. But that sleep is a missing piece in the explanatory puzzle of aging and Alzheimer’s is exciting. Because we may be able to do something about it.

MATT BRITTIN: Right. Because am I right in saying it gets harder to sleep as you get older? What changes, exactly?

MATTHEW WALKER: Yeah. So one of the myths is that older adults need less sleep. And that’s nonsense. Older adults need just as much sleep as they did when they were in their 40s or their 50s. The difference is that their brain cannot generate the sleep that it still necessarily needs. The reason is because parts of the brain that deteriorate most quickly and early during the course of aging are, unfortunately, the same centers that generate our deep sleep.

MATT BRITTIN: Right. OK. Wow. So you’ve covered a lot there. But you haven’t covered the role of sleep in road deaths. You touched on education. But tell us a bit more about some of the downsides that you’re increasingly clear on in terms of sleep-deprived populations.

MATTHEW WALKER: Yeah. So we’ve spoken a little bit about the brain. Let me speak a little bit about the body. I think the best place to start there is testicles– –because why wouldn’t you?

MATT BRITTIN: That’s what I always say, yeah. Why not?

MATTHEW WALKER: So what we know is that men who sleep five hours a night have significantly smaller testicles than those who sleep seven hours or more. In addition, men-

MATT BRITTIN: That’s relevant because?

MATTHEW WALKER: Well– –struggling to come up with an answer to that one.

MATT BRITTIN: Is it to do with fertility?

MATTHEW WALKER: Well, what’s also interesting is that if you look at the sex hormones, men who are sleeping four to five hours a night will have a level of testosterone which is that of someone 10 years their senior.


MATTHEW WALKER: So a lack of sleep will age a man by a decade in terms of that critical aspect of wellness. We see equivalent impairments in female reproductive health caused by a lack of sleep. So if you end up having a couple that’s trying to start a family, and they’re both underslept, it’s actually much more difficult to try and develop a genetic legacy in that regard.

MATT BRITTIN: Wow. OK. So in terms of sleep effect on the body, reproductive health.

MATTHEW WALKER: Reproductive health is the first one. I think the next one I would speak about is sleep and cardiovascular disease. The links there between a lack of sleep and heart attack and stroke, hypertension, are incredibly strong. I’ll give you just one example. Here, you don’t need a whole night of sleep deprivation. All it takes is one hour. Because there is a global experiment performed on 1.6 billion people across 70 countries twice a year. And it’s called daylight savings time.


MATTHEW WALKER: Now, in the spring, when we lose an hour of sleep, we see a subsequent 24% increase in heart attacks the following day.

MATT BRITTIN: Wow. That’s astonishing.

MATTHEW WALKER: But in the autumn, when we gain an hour of sleep, we see a 21% reduction in heart attacks.

MATT BRITTIN: It’s incredible.

MATTHEW WALKER: So that’s how, I think, fragile our bodies are to even the smallest perturbation of sleep. And by the way, you see exactly that same profile around daylight savings time for road traffic accidents, for suicide rates. You can even see this, by the way, in federal judges and their sentencing that on that Monday after losing one hour of sleep, the federal sentences are far more harsh, whereas in the autumn, if you get your sentencing, you actually get a more lenient sentence.

MATT BRITTIN: That’s incredible.

MATTHEW WALKER: You can see it all over. And that’s just one hour of lost sleep.

MATT BRITTIN: And I know you talk about the time of day that education starts. And you also talk about road accidents in the context of sleep, two really big social issues. So road accidents– you’re claiming here that sleep’s a bigger killer than alcohol or drugs in road deaths. Tell us why that is.

MATTHEW WALKER: So when you are underslept– if you’re severely sleep deprived, you can typically fall asleep at the wheel. But that’s usually not what happens. Most people are chronically underslept. They’re trying to survive on six hours of sleep or less. And what you typically then have are what are called microsleeps where your eyelid will just partially close, and the brain essentially just goes to sleep for a second or two.


MATTHEW WALKER: Now, if you’re traveling at 70 miles an hour on a motorway and you have one of these microsleeps for two seconds, at a moderate drift angle, you’re in the next lane, which means that you could be on incoming traffic. That’s the first issue. The second reason that drowsy driving is usually much more fatal in terms of it’s damaging, in terms of car crashes, is the following. When you’re drunk or you’re high, you typically react too late.

MATT BRITTIN: Right. So reactions are slowed down–

MATTHEW WALKER: Slowed down.

MATT BRITTIN: But you’re reacting.

MATTHEW WALKER: But you’re reacting.


MATTHEW WALKER: When you are sleep deprived, you don’t react at all because you have a microsleep. So at that point, there is a two-ton missile traveling at 70 miles an hour on the motorway, and no one is in charge. That’s why sleep-related accidents are usually much more deathly than drink driving or drugs.

MATT BRITTIN: That’s an amazing insight. And then on education, as a father of teenagers, I know this, the hour at which we start the school day and how that changes, particularly if somebody’s growing up from childhood through teens, our sleep needs seem to change in that period, as well. Tell us a little bit about that and the impact that you’ve identified there.

MATTHEW WALKER: I think this is a real problem that we’ve consistently started to roll back education times. It’s better here in the United Kingdom than it is in the United States. But I know that there was a push recently in the government level to try and delay school start times until 10 o’clock in the morning. That’s the bare minimum for a teenage brain. The reason is because as we go through adolescence, our biological preference for going to bed and waking up changes, that we move forward in time. We want to go to bed later, and we want to wake up later.

MATT BRITTIN: Why would that be? Do you know why that is?

MATTHEW WALKER: So we know the biology, and we know why it’s happening from a sort of a mechanistic standpoint. From an evolutionary standpoint, that’s an interesting question. I think one of the things that I posit in the book is that that’s the moment in time when you need to cut the cord from parental influence. You need to flee the nest, and you need to start testing the waters out by yourself in your own social community as you become a young adult. What better way to do that than actually, now, going to bed later than your parents? But yet your cohort, your brethren of that age, are also staying up later. And then you wake up later. So it may be a time when you can actually start to develop yourself as an adult independent of parental influence.

MATT BRITTIN: So my teenagers aren’t lazy. They’re just natural.

MATTHEW WALKER: They’re just doing simply what their biology does. And that’s one of the problems is that we have– sleep has a terrible image problem in society, that we label people who get sufficient sleep as slothful or even lazy. And I noticed that when you said, what about the people who get nine hours of sleep or more? And I see this all the time. These hands, these shamed hands go up. Yeah, yeah. And I have this at talks where there will be people who wait all the way to the end, and they don’t want to come to the mic and ask the question. And they’ll sidle up to me, and they’ll say, look, I’m one of those people who probably needs about eight or nine hours of sleep a night as if it’s this horrific thing to admit.

MATT BRITTIN: We should be cheering them on?

MATTHEW WALKER: We should be celebrating them and embracing sleep. And we don’t do that. And what’s strange is none of us look at an infant sleeping during the day and say, well, what a lazy baby. Because we know at that time of life, sleep is absolutely essential. But if you look at the data now, worryingly, somewhere between infancy and even childhood, we abandon the notion that sleep is important. And instead, we label it with these negative connotations. And so I think one of the problems is that school start times are too early. Based on some data that we’ve looked at, children of all ages, from five to 18, are now sleeping two hours less in this modern era than they were 100 years ago. To put that in context, if I went to my ethics board and said, look, I’d love to take a group of seven and eight-year-olds, and I’d like to deprive them of sleep for two hours every single night for the next month and study them, is that OK? they’d probably put me on academic probation, and rightly so.

MATT BRITTIN: Yeah. That’s what the world’s done.

MATTHEW WALKER: But yet that’s exactly what the world has done now across years of their life.

MATT BRITTIN: That’s amazing. So we could spend a long time talking about bad effects of not enough sleep. Let’s talk a little bit about the causes and then what you can do to improve, if we can. So you alluded to it there. One of the causes is, obviously, light, artificial light allowing us to extend the waking hours. But what causes bad sleep? What are the kinds of things that make us sleep badly today?

MATTHEW WALKER: So I think it’s important to separate out two things. One is having problems with sleeping. The other is having the opportunity to sleep. And both of those things will constrain your sleep. One of the problems with opportunity, the reason that most people don’t get the chance to sleep, even if they could sleep that amount, are– there are a number of reasons. Firstly, we are typically working longer hours, and we’re commuting for longer periods of time, which means that most people are leaving the house earlier and coming home later. Nobody wants to short-change their TV time or their family time. So the one thing that gets squeezed like Vise-Grips in the middle of the night is this thing called a normal eight-hour sleep period. Then we’ve also spoken about the stigma, the shame of getting sufficient sleep. Then you can start to come into the home and ask, what else is compromising your sleep? We certainly know that blue light emitted from devices can compromise your sleep. There’s a fascinating study where they had people reading on an iPad for one hour before bed versus just reading a normal book in dim light. And what they found was that the iPad reading– firstly, it delayed the release of a hormone called melatonin. And that hormone needs to be in high amounts to time the healthy onset of your sleep. But the iPad reading before bed decreased the amount of melatonin that was released by 50%. So it slashed it in half. And furthermore, it delayed the onset of that melatonin by about three hours. So you’re much closer to Russian time than you are UK time if you’re reading an iPad for one hour before bed.


MATTHEW WALKER: The third thing is that it disrupted their REM sleep. They had, actually, a reduction in their dream sleep, which is critical for things like mental health. So the invasion of, I think, technology into our environment, particularly blue light is a harm. But that’s not the only issue. I think technology is– and I’m mindful, of course, of where I’m speaking– but one of the things that technology can cause is just anxiety and stress. And a lot of people keep their phones in their rooms. And the first thing that they do when they wake up in the morning is hit your pin code and the tsunami of the world just invades you. And you train your brain to expect that every morning. It’s called anticipatory anxiety. And it lightens your sleep. It prevents you from going into the deeper sleep. So the advice there would be try to see if you can abstain from opening your phone until after you’ve brushed your teeth.

MATT BRITTIN: Yes. There’s a great advice, which is if the first thing you touch in the morning is your phone and not your partner, you’re in trouble.

MATTHEW WALKER: That’s right. Yeah. And that is not going to be a partnership that will last for too long

MATT BRITTIN: Pay attention, folks.

MATTHEW WALKER: And then just scale it back. Say could I not look at my phone until I’ve had breakfast? And there’s something so sublime about just going into a state of non-technologically invaded consciousness in the first five or 10 minutes. If you can’t do that, you probably need 20 minutes of delay time rather than 10 minutes. So I think that’s another problem, which is technology. We also know just general stress and anxiety. That’s the principal cause of insomnia. So now we’re shifting from things that are shortening your sleep duration to things that are preventing your sleep. So we are a dark-deprived society. We need that darkness at night. So trying to stay away from screens in the last hour before bed. Also dimming down the lights in your home. Drop the lights by 50%. You’ll be surprised at how soporific that actually is. I think one of the other aspects above and beyond stress, which is a key thing triggering insomnia, is alcohol and caffeine use.


MATTHEW WALKER: So this usually makes me deeply unpopular when I describe. I’m generally unpopular but this makes me even more unpopular. Firstly, caffeine. Caffeine, everyone knows, keeps you awake. It’s an alerting substance. It’s the only psychoactive drug that we readily give to our children without too much concern. But caffeine also is misunderstood in terms of its duration of action. So caffeine has a half-life of about six hours and a quarter-life of 12 hours. What that means is that if you have a cup of coffee at noon, half of that caffeine is gone by 6:00 PM. But it means that there’s still a quarter of that caffeine swilling around in your brain at midnight.

MATT BRITTIN: That’s amazing.

MATTHEW WALKER: So in other words, if you were to take a cup of coffee at noon, it’s the equivalent of getting into bed at midnight, and before you turn the light out, you swig a quarter of a cup of coffee, and you hope for a good night of sleep. And it’s probably not going to happen.

MATT BRITTIN: So what’s the latest I can have my coffee?

MATTHEW WALKER: I would scale back 14 hours before bed.



MATT BRITTIN: Can I have a lot of coffee early?

MATTHEW WALKER: So you can strategically drink caffeine to help wake you up. But if that’s the case, if you’re using caffeine before midday, you’re probably self-medicating your state of chronic sleep deprivation.

MATT BRITTIN: OK. If you’re using it early then you’re self-medicating. If you’re using it late, then you’re causing yourself a problem.

MATTHEW WALKER: That’s right.

MATT BRITTIN: Do you drink coffee?

MATTHEW WALKER: I’m decaffeinated all the way, which is not really– it’s not that bad in terms of–

MATT BRITTIN: Let’s take this all at once. Come on. Bring on the alcohol. Bring on the alcohol.

MATTHEW WALKER: So there’s only one other thing I’ll say about caffeine. Even if you’re someone who says, well, I can drink a cup of coffee in the evening and I fall asleep fine, and I stay asleep, so I’m unaffected, that’s not actually true. We’ve done some studies where we give you one single dose of caffeine, which is about 160 milligrams– standard cup of coffee– and then we measure your sleep that night. And typically, what you have is about a 20% reduction in the amount of deep sleep as a consequence of that coffee. To put that in context, I would have to age you by about 20 to 25 years to drop your deep sleep by 20%, or you could do it every night with a cup of coffee.

MATT BRITTIN: Wow. So alcohol, although it helps us to go to sleep, has a similar effect on the quality of sleep, doesn’t it? Are you going to tell us how bad?

MATTHEW WALKER: So it actually doesn’t help you fall asleep.

MATT BRITTIN: It doesn’t?

MATTHEW WALKER: So alcohol is a sedative. And sedation is not sleep. But when you have a nightcap, you mistake the former for the latter. So it helps you lose consciousness more quickly.

MATT BRITTIN: I’m feeling this is personal now.

MATTHEW WALKER: Yeah, yeah, I know. Maybe I should start looking at the audience rather than at Matt. So yes. You think that you’re falling into sleep. What you’re doing is you’re just knocking out your cortex. The second problem with alcohol is that it fragments your sleep so that you will wake up many more times throughout the night. So you have broken sleep. And that leads to, then, the next morning you’ll feel unrefreshed and unrestored by your sleep, which, by the way, usually leads you to then reaching for two cups of coffee rather than one. And it’s a vicious cycle. And then you need something to get you down at night, which is typically a nightcap. And it’s a vicious cycle. The third problem with alcohol is that it’s very good at blocking your dream sleep, your rapid eye movement sleep. So on all of those grounds, alcohol is best to be avoided.

MATT BRITTIN: So I want to come to questions from all of you in a couple of moments, if I may. But before we do that, let’s just talk a little bit more. You’ve alluded to, there, why we sleep, which is the whole title of your book and the huge benefits to our health and well-being from sleeping well. But what actually happens during sleep? What is the process? You mentioned REM sleep, dreaming. Just tell us a little bit about what’s going on and why it’s so important. What have you discovered?

MATTHEW WALKER: So let me tell you a little bit about how sleep works and then what it does. We all have two basic types of sleep. One is called non-rapid eye movement sleep, or non-REM sleep for short. The other is rapid eye movement sleep. And non-REM sleep is further subdivided into four separate stages– unimaginatively called stages 1 through 4, increasing in the depth of sleep. So stages 3 and 4 of non-REM are the deep stages of dreamless sleep.

MATT BRITTIN: Dreamless.


MATT BRITTIN: That’s when the body’s mending itself? What’s happening in those states.

MATTHEW WALKER: It is one of the times, one of the stages, where the body goes through a remarkable restoration. We see protein synthesis. We see rebuilding of cells. Deep sleep is probably one of the very best blood pressure medications that you could ever wish for. It’s during deep sleep that we get cardiac deceleration. Your heart rate plummets. Your blood pressure drops. It’s essentially a reset for your cardiovascular system. It’s also during deep sleep, but also REM sleep, when you restock the armory of your immune system. And that’s why when you start to sleep less, you’re far more vulnerable to infection. In fact, if you’re sleeping five hours a night, you’re four times– 400%– more likely to catch a cold than if you’re sleeping eight hours or more. Another demonstration of this is if you get a flu shot, and we’ll be four months away from that time period, but you’re not getting enough sleep, if you’ve only been sleeping, let’s say, five or six hours in the week before you get your flu shot, you only produce half of the normal antibody response, rendering that flu shot largely useless. Because your immune system is so impoverished that it can’t respond to the antigen.

MATT BRITTIN: These are massive numbers you’re quoting here in terms of the impact of these things– huge.

MATTHEW WALKER: Yeah. And why is that? Why can I quote such large numbers? Is it just a lot of hand waving and plucking of the cherries in terms of the data. And the answer is no. And the reason is this– human beings are the only species that deliberately deprive themselves of sleep for no apparent reason. And the reason I make that point is mother nature has, therefore, never had to face the challenge of sleep deprivation throughout the course of evolution. So she’s never had to come up with safety nets to risk mitigate this when it happens. Now, there is precedent in biology for that. Why can’t we, for example, bank sleep and then use it when we’re going to be sleeping deprived? That would be lovely. And there is a method like this in biology. It’s called the fat cell. Because there were times during our evolutionary past when we faced feast and then we had famine. So mother nature, facing that challenge, created this thing called the adipose cell, the fat cell, so you could store caloric credit and then spend it when you had a debt, when you had a famine. Where is the fat cell for sleep?

MATT BRITTIN: Oh, you should invent that.

MATTHEW WALKER: I would love. I would make so much money out of it. But the reason it doesn’t exist is because we’ve never had that challenge. Humans are the only species that do that.

MATT BRITTIN: It’s amazing. So you were talking, then, about non-REM sleep and the going deeper and deeper.

MATTHEW WALKER: Yeah. So those two types of sleep will play out in a battle for brain domination throughout the night. And you’ll start to gradually, as you fall asleep, go into the light stages of non-REM, then down into the deep stages of non-REM, and then after about 60 or 70 minutes, you’ll start to rise back up, and you’ll have a short REM sleep period. And then you go back down again, down into non-REM, up into REM.

MATT BRITTIN: Right. So the REM sleep you haven’t touched on. So tell us a bit about that. That’s when we’re dreaming and [INAUDIBLE]..

MATTHEW WALKER: Yeah. And in fact, when you look at the brainwave activity in dreaming, it’s indistinguishable from that when we’re awake. In fact, some parts of your brain are up to 30% more active when you’re in REM sleep than when you’re awake.

MATT BRITTIN: So some parts of your brain are more awake than when you’re awake.

MATTHEW WALKER: That’s right. They’re more active when you’re in REM sleep than when you’re awake. Other parts of the brain, however, switch off.

MATT BRITTIN: Because we parallelize ourselves, don’t we?

MATTHEW WALKER: We do. So when you go into dream sleep, which is rapid eye movement sleep, the brain essentially paralyzes the body so the mind can dream safely. It stops you acting out your dreams. So every time you go into dream sleep, you are locked down into an incarceration of the body. You cannot move. You can’t speak out. And that’s a safety mechanism. As we get older, in some people, particularly males, that part of that lockdown of the body begins to fail, and you start to act out your dreams. It’s called REM sleep behavioral disorder. But for the most part, most of us are not doing that.

MATT BRITTIN: I’m worrying about that now.

MATTHEW WALKER: It’s a 90-minute cycle.

MATT BRITTIN: How old do you have to be for that?

MATTHEW WALKER: It usually starts in people in their 50s.


MATTHEW WALKER: And one of the difficult things is that if you have REM sleep behavioral disorder, it markedly increases your risk probability of Parkinson’s disease, we’ve been finding. So there are things in your sleep that can foretell, that can forecast, your disease risk 10 or 20 years ahead of time. And this is a lot of work that we’re doing right now at the Sleep Center. How can we use sleep as a new biomarker that is predicting your disease risk decades ahead of time? And the reason that that’s important is because right now in health care, we actually don’t have a model of health care. We have a model of sick care, which is that we are principally interested in treatment. What we need to have is a model of truly health care. If you do that it’s a model of prevention, not a model of treatment. And if you can find things that are foretelling your disease risk way ahead of time, you give yourself the opportunity window to do something about it. And sleep seems to carry within it, nested in its static of electrical brainwaves at night, it seems to have lots of these health biomarkers that are disease risk protective or predictive.

MATT BRITTIN: When I was reading about REM sleep in your book, you mentioned not just the fact that some parts of our brain are more active but also that we’re replaying the days memories at 20X normal speed. And there’s a theory that we’re defragmenting and filing in that sleep. But what really is going on in REM sleep?

MATTHEW WALKER: So in the studies with rats, what they’ve done is they’ve had them run around a maze, and they’ve put electrodes in the brain. And you can pick up this electrical signature of learning as it’s running around the maze. And let’s say that you just make each one of those brain cells have a tone to it. And so the rat is running around the maze, and you just hear this brain cell firing as its coding the maze. And it sort of goes up ba-ba-ba-bum, ba-ba-ba-bum, ba-ba-ba-bum. And then what was fascinating in those studies is that they then let the rats sleep. And what you heard was this replay– ba-ba-ba-bum, ba-ba-ba-bum– but it wasn’t at that speed. It was 20x. So it was like [WHIRRING].

MATT BRITTIN: So it literally is happening. That’s incredible.

MATTHEW WALKER: And so what we see is that the brain is actually, essentially, replaying those memories, almost as though what it’s doing firstly is scoring the memory trace, or etching the memory trace, more powerfully into the brain so that when you wake up the next day, you can better remember the things that you learned before. And we know that sleep is wonderful for doing that. That actually happens during deep non-rapid eye movement sleep. What happens during REM sleep is something more interesting. There, the brain almost becomes chaotic and random. And what we think is happening during REM sleep is that during deep sleep, you take the information you’ve learned, and you save it. You hold onto it. Then it’s during REM sleep that we say, based on the information that we’ve learned today, how does it interrelate with everything that we’ve previously learned? How do we figure out which connections we should build and which we should let go of? And it seems as though dream sleep is a form of informational alchemy. It’s almost like memory pinball. You start bouncing it around the attic of all of your memories and saying, should this be a connection? Should this be a connection? But REM sleep is almost like a Google search gone wrong. It’s during REM sleep that you input your search term, and it immediately takes you to page 20, which is about some bizarre thing. You think, hang on a second. Is there a really– but there’s a strange, tangential link. It’s during dream sleep that we test out the most bizarre, strange, associative connections. And that’s the reason that you wake up the next morning often having divine solutions to previously impenetrable problems. That’s what dream sleep seems to be about, as well.

MATT BRITTIN: Wow. It’s incredible to understand just the beginnings of that and how it works. And so I’d like to invite people to come to the mic. We have our first questioner here. Do you want to speak up and find out about sleep?

AUDIENCE: Just a quick [INAUDIBLE] this is working. Yes. Do you have any tips on dealing with jet lag? So anything we can do to improve?

MATT BRITTIN: So our bodies were never designed to be fast forwarded through time with this thing called a jet engine. And it causes a biological lag, a mismatch, between your internal clock and the place that you arrive. And that’s what we call jet lag. There are some “treatments,” quote unquote, but there is no cure. The treatments are probably the following. The first is most people sleep at the wrong time on the flight. So let’s say I’m traveling from San Francisco back to London. The first thing you need to do, as soon as you get on the plane, is change all clocks to the new time zone. So you’re now immediately reminded what you’re working with in terms of a time structure. The second, most people on that flight over from San Francisco are probably going to be sleeping in the second half of the flight. Now, I will touch down at around about 11 o’clock in the morning. That means that most people are sleeping on London time from about 7 o’clock in the morning through until 11 o’clock in the morning. Why is that a problem? The longer that you’re awake throughout the day, the more sleepiness that you build up in the brain. It’s a chemical called adenosine. The sleepier that you are, the more likely you are to fall asleep and stay asleep. But one of the problems is that if you sleep too late on the flight, essentially, it’s like waking up at 11 o’clock in the morning. And then, when it comes to go to bed at the normal time in London, you’re not going to be tired because you were sleeping until 11:00. So sleep in the first half of the flight, then brute force yourself awake. Stay awake. And then stay awake for the entirety of that following day. Don’t be tempted to nap. Because if you nap, again, you release some of that sleepiness. It’s almost like a pressure valve on a cooker. And it will make it that much harder to fall asleep that following evening. That first night, if you nail that first night with a good night of sleep, it’s a great way to reset your biological clock. Once you’re in the new time zone, two more recommendations. The first is in the morning, go out and get daylight, at least 20 to 30 minutes outdoors. When you do that in the morning, even if it’s sunny, don’t wear sunglasses. I know it’s cool. But you need to get that light into the brain. The other one is eat at the regular times when everyone else is eating, not when you’re hungry. Because food, we’ve discovered, is just as powerful a resetting trigger on your internal clock as light is. And then, if you want to, you can strategically use melatonin. It’s not available over here, but it’s available in other countries. Usually take that about an hour before bed. Most people dose too much. They usually do 5 to 10 milligrams. It should really be 0.5 to 3 milligrams. Just be mindful, however, that if you get it in America, it’s not regulated by the government. One study found that if you looked at 20 brands, based on what it said on the label, what was actually in those pills were either 80% less than what it said on the label up to 160% more than what it said on the label. So it’s a bit of a Wild West. You’ve got to be careful. But those would be the tips for jet lag.

AUDIENCE: Thank you.

MATT BRITTIN: It’s a mine field. Great tips. And actually, one other thing while you’re on the subject of travel, because quite a few of us do, is sleeping somewhere unfamiliar also has an impact on your sleep. Just tell us a little bit about that because it’s also useful for this group.

MATTHEW WALKER: It is. So you will sleep almost with one half of your brain differently than the other when you travel. So there are some species, like dolphins, for example, who can sleep entirely with one half of their brain. Otters do this. Most aquatic mammals have what we call unihemispheric sleep, which is that one half of their brain is awake, the other half is asleep. And when that half has had its fill, it switches over. Now, wouldn’t it be lovely if we could do that? You could keep working, and one half of your brain is sleeping, and then it switches over. But humans, actually, we didn’t think they could do that. But they have sort of a diet version of that, a lite– L-I-T-E– version of that. Whenever you sleep in an unfamiliar location, what we found is that one half of the brain does not sleep as deeply as the other half of the brain, almost as though it’s trying to keep watch and maintain some degree of vigilance. And that’s probably the reason why a lot of people will say that first night in the hotel–

MATT BRITTIN: You never feel as good, yeah.

MATTHEW WALKER: –never feels good. I never quite sleep. Or this phrase, I can’t wait to get back to my own bed. In some ways, it’s familiarity. In other ways, it’s the depth of your sleep, as well.

MATT BRITTIN: Truly fascinating. Next question.

AUDIENCE: Hi, Matthew. My name is Alice. I have a 10-month-old boy and a four-year-old boy. I don’t get a lot of sleep. You’re scaring the life out of me right now.

MATTHEW WALKER: Well, it’s actually the lack of sleep that’s taking the life out of you right now. But let’s not rush to judgment. Let’s see what we can do before we make that classification.

AUDIENCE: And I suppose my question is I try to sleep when I can, and I try and catch up as much as possible. But I’m not getting as much as I need in this period. When I get through this, how is my health going to be in, say, a year or two, when I’ve caught up and they’re sleeping through the night and all that kind of stuff? Are there long-term effects. You mentioned the sleep bank. I recognize you can’t bank sleep. But can you catch up once you start sleeping well again?

MATTHEW WALKER: Great question. So I think parenting– immensely difficult. You’re doing the right thing in the sense of being opportunistic about your sleep. Get it when you can. At that stage, you’re going to be chronically underslept. Also trying to help kids, as well, one of the things is routine. That can really help them. Just find a routine that works and then stick to it religiously. Also, for kids, taking toys out of the bedroom is a recent finding that that actually means that the bedroom is this thing other than sleep, and toys become a trigger, and they actually sleep worse when they’ve got toys in the bedroom. So get those out, as well. Do something calming and relaxing with them in the hour before bed– typically, reading, doing a puzzle. Hot baths are a great thing– great thing for all of us. And the reason is because you need to drop your core body temperature by about 1 degree Celsius to initiate sleep and then to stay asleep. It’s the reason that you will always fall asleep easier in a room that’s too cold than too hot. But what happens– and you think, well, hang on a second, you’re telling me to take a bath, doesn’t that warm me up? It’s actually the opposite. When you get into a bath or you bathe a child, all of the blood rushes to the surface. And when you get out of the bath, all of the heat is radiated out of the body. So your core body temperature actually plummets, which means that you fall asleep faster and stay asleep. So trying to help kids sleep better will ultimately help you sleep better. But to come to your question, yes, sleep is not like the bank that the damage that is happening is happening, and you can’t necessarily reverse that damage. However, it is never too late to start sleeping better. And when you start sleeping better, your health outcome will stabilize. And I’m not just saying that to be optimistic. We know the data. For example, there’s a study where we looked at people who had untreated sleep apnea, which is snoring. And by the way, if anyone listening is a snorer or they know of someone who is snoring, go and get their doctor to do a sleep test on them. Sleep apnea, which is heavy snoring, is a killer in terms of a disease. And 80% of people who have it are undiagnosed. So these people had sleep apnea, and they were given a treatment, which is this face mask to help open up their airway. Turned out that about half of the people adhered to the treatment. The other half didn’t. And then you track them for 10 or 15 years. What you find is that those people who adhered to the treatment, whose sleep improved– now, these were people in their 50s– once they started sleeping better, they staved off the onslaught of Alzheimer’s disease by almost 10 years relative to that other group, who didn’t comply to the treatment and, therefore, continued to sleep badly. It is a causal piece of evidence that even in mid to later life, if you correct your sleep you improve your long-term health outcome.

AUDIENCE: Thank you.

MATTHEW WALKER: You’re welcome.

MATT BRITTIN: Trouble is, of course, when your kids are a year older, you’ve still got all of the next 15 years to go.

MATTHEW WALKER: Good luck. Sleep well.

MATT BRITTIN: How many people currently got young children. So we’ve actually quite a lot of very sleep-deprived people in the room.

MATTHEW WALKER: Yeah. The nice thing is all of the frightening and terrible and damaging things that I’m telling you, you won’t remember any of these because you’re so insufficiently slept that you’ll wake up tomorrow morning, you’ll think, ah, everything’s just fine. You won’t worry. Yes.

MATT BRITTIN: Time for a couple more questions.

AUDIENCE: Hi, Matthew. First of all, thank you for an absolutely fantastic book. You’ve got a fan for about a year and a half. And I think everybody should read it. The one question I’ve been struggling to answer to myself is when do I know that I’ve had enough sleep? And one thing that wasn’t clear to me from the book is I think there is this proverbial waking up, opening the window, dancing in the street, everything is great, I’ve had a good night’s sleep. I haven’t had that in the past 10 years, and I doubt many people here have. What I find is I wake up on Saturday. I don’t set the alarm. But then I roll in bed for a couple of hours. There’s this weird half-slumber. I kind of drift in and out of sleep. When do you actually know that it’s time to get out of bed, without setting your alarm, supposedly? When would you do that.

MATTHEW WALKER: Yes, it’s a great question. It’s very difficult to figure that out just at the weekend because at the weekend, what you’re doing is you’re trying to sleep off the debt that you created during the week. And this is why most people will often say to me, well, when I sleep late during the weekend, sometimes I feel worse. It’s almost like I go to sleep hangover. So there’s this thing called too much sleep, and it’s bad, and I shouldn’t be sleeping as much. No, what you’re doing there is you’re just having a hangover because your brain is trying to get what we call recovery sleep. And it will still feel heavy on you. So what you need to do is an experiment where if you can structure your work schedule, you just say, I am not going to set an alarm. And I am just going to let my sleep unfold naturally. Now, to begin with, the biggest fear is that you’re going to oversleep, and you’re going to turn up to work late. And that may happen for the first couple of days. But gradually, what will happen is that you will sleep off some of that debt, even though you can’t make it all back, and you will throttle back, and you will find a sweet spot. And then you will just start waking up naturally. One of the issues you have to ask yourself, though, is when am I designed to sleep? And it’s called your chronotype. So everyone here has a chronotype. Are you a morning type? Are you an evening type? Are you somewhere in between? It’s what we call owls and larks. Now, you don’t get to decide that. It is genetically hardwired. It’s gifted to you at birth. There is no choice. How do you figure out what type you are? Well, if you were to be on a desert island with no commitments, no one to wake up for, just ask yourself, what time would I probably like to go to bed, and what time would I probably like to wake up? That’s probably your chronotype. When you sleep in sync, in harmony, with your chronotype, that’s when you get the very best quality of sleep. If you sleep in a mismatched fashion with your chronotype, you won’t get good sleep, and you will struggle with sleep. A good example of this is night owls who would like to go to sleep, let’s say, at midnight or 1:00. They will often come to me saying, look, I’ve got terrible insomnia. I lie in bed for the first two hours, and I just can’t fall asleep. And I’ll say, well, what time are you going to bed? And they say, I go to bed at 10 o’clock because I have got to be awake at 6:00. Well, there, you’re two hours early relative to your natural, biological edict. And so no wonder you’re going to be lying in bed awake for the first two hours. Because your body is not yet ready to generate the sleep that it needs. And it masquerades as insomnia. You don’t have insomnia. You just have a mismatch between when your biology wants you to sleep and when you’re trying to sleep. So finding out what your chronotype is and then finding how to match that with your sleep is the best chance for good sleep.

MATT BRITTIN: You also suggest, don’t you, regular pattern, so trying to go to sleep at the same time and get up at the same time. This whole idea of weekend recovery doesn’t really cut it for you.

MATTHEW WALKER: No, it doesn’t. And what people typically do at the weekend, they will sleep in by, maybe, two or even three hours, and they’ll be staying up later. And then, come Sunday night, you’ve got to drag your biological clock all the way back by two or three hours.

MATT BRITTIN: Makes Monday even worse.

MATTHEW WALKER: And it makes Monday worse. And we actually see that in terms of productivity, this sleepy Monday effect is what we call it. But one of the problems there is that that’s torturing your biology. It’s essentially like flying back and forth from Moscow to London every single weekend. And your body does not respond to that. And that’s the reason that when we see in people who do night shift work that their disease risks are astronomically higher. In fact, the link between a lack of sleep and cancer has now become so strong that the World Health Organization has classified any form of nighttime shift work as a probable carcinogen.

MATT BRITTIN: That’s astonishing. So you don’t want to do shift work, basically.

MATTHEW WALKER: No. And you don’t want to create what’s called social jet lag, which is artificial shift work, by sleeping in late, going to bed late at the weekend. Just try and keep it regular is the best advice.

MATT BRITTIN: Party early, people. OK.

AUDIENCE: Amazing. Thank you so much, Matthew. I really enjoy your talk. I see that you are wearing Oura ring. Do you have recommend this device as to track sleep? And my second question– sorry about that– is how do we take naps more effectively? Because we have so many napping pods in office.

MATTHEW WALKER: Yeah, two great questions. So I am wearing an Oura ring. I don’t have any affiliation with the company. I’ve tried out just about every sleep tracker out there. I love technology. What I would say right now is most of these sleep trackers are probably much of a muchness in terms of the accuracy of separating non-REM sleep from REM sleep from light sleep, deep sleep. So I wouldn’t get too hung up if these devices are telling you you’re having very little deep sleep. If I brought you into my laboratory, the accuracy there would be the truth-telling thing. I think one of the interesting things about sleep trackers, though, is the form factor. When we go to bed, we take things off. We don’t put things on. So I’m actually very enamored right now with this idea that I would term unwearables for sleep rather than wearables for sleep. And so I think putting things on your head, putting things on your wrist, strapping things to your chest, I think those things are probably not going to result in a great deal of stickiness. I think the ring is probably the second-least intrusive thing. I think the best device, ultimately, is probably going to be the bed itself. You think about your car nowadays. It’s packed full of sensors. It’s remarkably technologically capable, whereas 60 years ago, your car was very rudimentary. Well, think about your mattress. Your mattress now, 60 years on, is pretty much the same as it was 60 years before. Why isn’t it packed full of just as many sensors and tracking the health of you as much as your car is being tracked in terms of its own mechanical health? So I think if you were to ask me to rank order which devices are ultimately going to be the best for tracking sleep, I think probably the mattress is going to be the best one. There, you can fall into bed drunk, and you’ll still get your sleep measured, where you don’t have to worry about charging it.

MATT BRITTIN: And just one minute on napping.

MATTHEW WALKER: Yes. So naps can be a benefit. We’ve done some studies with naps. They can provide improvements for both brain and the body. You can get your eight hours of sleep by way of sleeping one long bout at night and then a nap, like siesta-like behavior. In fact, when we’ve looked at hunter-gatherer tribes whose way of life hasn’t changed for thousands of years, they have biphasic sleep. They sleep from about 9:00 to about 5:30, 6:00, and then they have this siesta-like behavior. By the way, have you ever wondered what the term midnight actually means? The middle of the night. And in those cultures, that’s exactly what it is for them. But for us now, in modernity, it’s the last time we check email or we think about posting that last thing. But I think the point here is that naps can be beneficial but with a big caveat, which is that if you are struggling with your sleep at night, do not nap during the day. Because it comes back to that sleepiness signal. As you’re awake across the day, you’re building up all of that healthy sleepiness. And when you sleep, you remove it so that you wake up feeling refreshed. But if you take a nap in the afternoon, you release some of that sleepiness, and it can make it harder to fall asleep or stay asleep at night. So if you are not struggling with sleep and you can nap regularly, naps are just fine.

AUDIENCE: Awesome. Thank you so much.

MATT BRITTIN: We are pretty much out of time, so I’d like to just ask a closing questions, so a quick answer from you, if I may. So lots of advice on how we can sleep better and look after our sleep better. So what are the top things that we should all be doing and thinking about if we want to have better health through sleep?

MATTHEW WALKER: So I think we’ve touched on many of them. Regularity is king– go to bed at the same time, wake up at the same time. Get your darkness in the evening. That’s critical. Drop your bedroom temperature. Get it cold, so you can initiate sleep. Probably about 18 degrees Celsius is optimal for the sleep of most people. It sounds cold.

MATT BRITTIN: It’s quite cold.

MATTHEW WALKER: But put thick socks on. Have a hot water bottle at the end of the bed. That’s fine, but cold it must be. And we’ve spoken about alcohol and caffeine, so I’ll dispense with those. The last thing I would say is do not lie in bed awake for very long. So if you haven’t fallen asleep after 15 or 20 minutes, or if you haven’t fallen back asleep after that same period, don’t stay in bed. Get out of bed. Go to a different room. And in dim light, just read a book. An only return when you’re sleepy. And the reason is that your brain is so associative that it will very quickly learn that your bedroom is the place of being awake rather than being asleep. And you need to break that association. And so by coming back only when you’re sleepy, you will relearn the connection that your bedroom is the place of sleep, not about wake. So you would never sit at the dinner table waiting to get hungry. Why would you lie in bed waiting to get sleepy? And the answer is you shouldn’t.

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