Instant Genius - Sleep, with Dr Matthew Walker

Episode Date: July 25, 2021

Dr Matthew Walker, professor of neuroscience, tells us about how sleep evolved and what happens when we don’t get enough. Once you’ve mastered the basics with Instant Genius, dive deeper with Instant Genius Extra, where you’ll find longer, richer discussions about the most exciting ideas in the world of science and technology. Only available on Apple Podcasts. Produced by the team behind BBC Science Focus Magazine. Visit our website: sciencefocus.com Hosted on Acast. See acast.com/privacy for more information. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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Hello and welcome to Instant Genius, a bite-sized masterclass in podcast form. Each week, you'll hear world-leading scientists and experts talking about the most fascinating ideas in science and technology today. I'm Thomas Ling, staff writer at BBC Science Focus magazine, and in this episode I'm joined by Matt Walker. He's a professor of neuroscience at the University of California, and best known as the author of International Bestseller Why We Sleep.

And sleep is just what is here to talk about today, unpacking the science of how it first evolved and the profound biological impacts of not getting enough. Hi Matt, welcome to Winston Genius. Well, thank you very much for having me, Thomas. It's a pleasure to be with you. So today, I wanted to start with a really easy question for you. But instead, I'm going to ask the really big one.

Why is it that humans sleep? That's a great question. And, you know, 40 years ago, we would say that the reason we sleep is to cure sleepiness. which is a profoundly unhelpful and unscientific answer. You know, that's the equivalent of saying, well, we eat to cure hunger. That tells you nothing about the nutritional sustenance and physiological benefit that food provides. But that was the best that we had in some ways 40 years ago. Now, based on all of the research and it's hundreds of thousands of research studies,

we've actually been forced to upend the question and ask, is there anything in the brain or the body that sleep doesn't support? And so much so that we can now say that every major physiological system in the body and every operation of the mind is powerfully enhanced when we get sleep and demonstrably impaired when we don't get enough. So it's perhaps a slightly circular answer, but suffice to say that we sleep for a whole consternation. of nighttime benefits, both for our brain and also for our body. And you can also, you know,

imagine that would have to be the case, surely, because from an evolutionary standpoint, sleep is the most idiotic of all behaviors. You know, firstly, we're, you know, we're not finding a mate, we're not reproducing, we're not caring for our young, we're not foraging for food, and worse still, you know, we're vulnerable to predation. Now, on any one of those grounds, but especially all of them as a collective, sleep should have been strongly selected against during the course of evolution. However, sleep has fought its way through every step along the evolutionary pathway. So much so that it's often been said if sleep doesn't serve an absolutely vital function,

then it's the biggest mistake that the evolutionary process ever made. And we now, of course, understand that Mother Nature didn't make a spectacular blunder in creating this thing called sleep. So, so do you kind of see sleep as self-improvement then? So what are the sort of the main benefits of getting sleep? I would even go further than that. Sleep is more than self-improvement. It's more than an optional lifestyle luxury. Sleep is a non-negotiable biological necessity.

You know, it is your life support. system. And it is probably Mother Nature's best effort yet at immortality. So you sort of touched on it there about the idea of sort of sleep evolving. Do we have any idea of how it evolved in the first place? We know, obviously short of a time capsule where we can race back and really understand that question. We can use the lens of evolutionary biology to try and understand that. And what we know is that very ancient evolutionary creatures, things such as earthworms, etc. Even they have periods of what we think of as sleep. It's called letharges.

So where they go into this state of lethargic behavior of inactivity. So they have active phases. They have passive phases. It looks very much like the precursor of wake and sleep. And those are, of course, hundreds of thousand millions of years old, in fact. And we even understand that there are certain forms of bacteria that will have these active and passive phases and, you know, some of the most rudimentary and early evolutionary forms of life that appeared on this planet, which is to say that perhaps sleep evolved with life itself on this planet and has persisted, you know, through until this day, every species that we've studied to date sleeps. And what that tells us is that sleep must be absolutely essential if all of those species display something that looks like sleep. So that's perhaps one answer. I would, however,

give you my own slightly different answer, which I think is probably a little bit controversial, but here goes. And unfortunately, we really can't test this scientifically. It's a hand-waving theory. Why do you and I both assume that sleep evolved? In other words, what about the situation were sleep never evolved, meaning that sleep was the default state for all life on this planet, and it was from sleep that wakefulness emerged. So sleep never evolved, it was from sleep that wakefulness emerged, and then we have to return back to the default state of sleep each and every day.

And in that sense, sleep is the price that we pay for wakefulness. So, fast forward, like I said, a few million years then to the current day. And often if sort of humans are talking about sleep now, like most people, myself included, will probably say that they don't get their recommended eight hours. But what about those sort of people who claim that that's fine and they can just get away with just four hours? Are they telling the truth they're okay? Well, they may be telling the truth about how much sleep that they're getting, but unfortunately, when it comes to, you know, them doing, you know, in a quote, okay,

that unfortunately is not going to be the case. And it's not going to be the case for several different reasons. Firstly, we know that the number of people who can survive on less than six hours of sleep and show no impairment in either the brain or the body, rounded to a whole number and expressed as a percent of the population is actually zero. So, no, it's very unlikely that they are doing okay in that sense. The other thing I would say, too, and I don't mean to be flippant in that sense, but your subjective sense of how well you're doing when you are not getting enough sleep

is a miserable predictor of objectively how you're doing when you're not getting sufficient sleep. So, you know, the analogy perhaps would be a drunk driver at a bar. You know, they've had a couple of pints and they've maybe had a couple of shots and they pick up their car keys and they say, look, I'm fine to drive. And your response is, no, I know that you think subjectively that you're fine to drive, but objectively trust me, you're not fine. and that's the problem with sleep deprivation as well. We don't know that we are insufficiently slept when we are not getting sufficient sleep.

And so that's the other reason why I think a lot of people will say, no, actually, you know what, I can get by on just four or five hours of sleep a night. Now, that's not to say that there aren't some people who do seem to be short sleepers. And we know of these individuals. They are a certain genetic sort of, well, mutation is, is a slightly perhaps triggering word, but in some ways they are genetic mutants. And what we've discovered, and we know the genes, one of these genes is called the DEC2 gene or the DEC2 gene, and these individuals seem to be able to survive on as little as six hours and 15 minutes of

sleep. And they truly don't show any impairments, not at least that we've been able to measure so far. So there are some people who can survive on less than seven hours of sleep, but for most of us we need for the average adult, somewhere between seven to nine hours is the recommended amount. So are there some people who can go in the opposite direction, so people that might need more than their nine hours? Yeah, it is a great question. There are some people who are long sleepers, and if you are listening to this and your sleep, your sleep need you feel is, let's say 10 hours, and you feel refreshed and restored by that sleep, that's an important part of this. Then that's not a problem either. There's no need to get worried. There is a clinical condition,

however, that we call hypersomnia. And that plays out in two different flavors. One of them is where people report sleeping long or being in bed long, and that typically happens in the condition of depression. But if you look at that literature, it turns out that it's equivocal. because when you ask those people, most of those questionnaires have said, what time were you in bed and what time did you get out of bed? And of course, with depression, most people just don't want to face the day, so they will often stay in bed longer. And therefore, we assume that that answer of,

this is the time I got into bed and this is the time I got out of bed, is the amount of time that they slept, which then looks like it's 10, 11, 12 hours. So it's unclear if there is that situation. The other situation that we call hyposomnia is where people are getting a lot of sleep at night, but they still feel sleepy and unrestored and unrefreshed by their sleep during the day. And so they feel as though they just can't function. So they have increased sleepiness during the day.

And that's what we also call the condition of hypersomnia or hypersomenolence. So those are two conditions where we do see perhaps this idea of quote unquote too much sleep. but let's go further than that. Could there actually be outside of the clinical domain for people who are, you know, not, who are medically healthy? Could there be such a thing as too much sleep? Well, it may sound strange coming from someone like me, but I actually think, yes, there could be such a thing as too much sleep.

But rest assured, that's no different than the three other main critical ingredients of life, food, oxygen, and water. Can you overeat? Yes, of course you can. And can you underease? You can too. Can you overhydrate? Yes, hypondremia. And it's something that happened, for example, in the 1990s. And during the ecstasy craze, governments were saying, look, you're dancing all night, you're getting dehydrated, drink lots of water. People were drinking too much water and they were diluting their levels of electrolytes such as sodium. They were having cardiovascular events, stroke, because of

increased blood pressure. So you can have too much water, just like you can have too little water. can you have too much oxygen? Yes, it's called hyperoxemia, and it can damage brain cells. So there is this sort of U-shaped function to many of these critical life ingredients, and sleep, I think, is probably no different. You know, it's the Goldilocks syndrome. Not too little, not too much, just the right amount. So that's too much sleep. So what about not enough? So what does sort of losing just one hour's sleep due to your body? We actually know that answer, and it's perhaps the largest sleep experiment ever performed.

And it happens on about 1.6 billion people across 75 countries twice a year. And it's called daylight savings time. Now, in the spring, when we lose one hour of sleep opportunity, for example, we see a subsequent 24% increase in heart attacks the following. day. Yet in the autumn, in the fall, depending on where you are, when we gain an hour of sleep opportunity, there is a 21% reduction in heart attacks. I find that absolutely incredible. And we see exactly the same profile for things such as road traffic accidents on our streets, tragically suicide rates as well, follow a similar pattern. We've even recently discovered

that the harshness of the sentencing of federal judges in the United States is also dependent on that daylight saving shift, and they will dole out harsher sentences on the day after losing one hour of sleep because their mood and their emotions are so impacted by that one hour of lost sleep. And, you know, of course, many of us perhaps think very little of losing one hour of sleep, but there are demonstrable, demonstrable, impairments that we can measure. Why is it that we become more sort of moody and our emotions change when we don't have enough sleep?

Like even just that one hour? We've done a lot of work in this area to understand the relationship. There is a very tight and a very intimate relationship between your sleep health and your mental health. First, what we know is that if you take people and you deprive them, let's say, for a whole night of sleep, And then you place them inside a brain scanner, which is what we've done, and you show them different

sort of emotional images, and you take snapshots of brain activity as you're doing this. And then you compare that pattern of brain activity relative to those same people when they've had a full night of sleep. What do you see? Well, firstly, what we found was that the deep emotional centers of the brain, particularly an area that we call the amygdala, which is one of the centerpiece regions for the generation of strong negative reactions. That was erupting with hyperactivity when you had not got enough sleep, when you've not obtained enough sleep, I should say. In fact, that part of the emotional brain was 60% more reactive when you hadn't had a good night of sleep. But what we also found was the

explanation as to why. Why does your emotional brain become so hypersensitive? And the answer was that another part of your brain called the prefrontal cortex, which sits directly above your eyes, that part of the brain had been shut down by sleep deprivation. And that's important because that's the sort of the CEO of your brain. It's very good at making high-level, top-down executive control decisions, and it regulates our impulses and our emotions. And because we'd lost and would severed that connection between the most human part of your brain, the prefrontal cortex,

and that deep Neanderthal emotional center, it was almost as though you are all sort of emotional accelerator pedal and too little emotional break, as it were. And that's one of the reasons. It's one of the many reasons why we become so emotionally erratic, so emotionally unstable when we haven't been getting the sleep that we need. So if someone has lost that one hour's sleep, they're feeling a bit moody. while simply sleeping an hour extra the next night to sort of make up for this? Not really, no. So what we found is that for a number of different things, things such as learning, memory, such as emotions, even the cleansing of the brain of all of the metabolic toxins that accumulate as we're awake,

it doesn't seem as though you can sleep back what you've lost, which is to say that sleep doesn't seem to be like the moment. bank in that sense. You can't accumulate a debt and then hope to pay it off at some later point in time. So sleep in terms of things like learning in memory, it's an all-and-or-nothing phenomenon. So if you don't snoo as you lose, I guess would be the answer to that question. So now that's not to suggest that if you have the opportunity to sleep a little bit longer, you shouldn't. I would still say that that may be a helpful thing. But in truth, as a sleep advocate and a scientist, and sleep clinicians will tell you this too, we really advise regularity, go to bed at the same time,

wake up at the same time, no matter whether it's the weekday or the weekend. Try not to do that sort of what we call social jet lag at the weekend or what I would think of as almost sleep bulimia, which is where we sort of binge at the weekend and then we sort of of, you know, we're restricting during the week on our sleep. That binge, purge, abstinence sort of profile, it's really not ideal for your sleep. So, you know, let's say that you and I, we would normally be trying to go to bed at, let's say, 11 a.m., sorry, 11 p.m. most nights. And then at the weekend, you know, we go out, Friday, Saturday, and we stay up until 1.32, and we wake up, you know, three hours later as well. And then come Sunday night, we've got to drag on.

biological body 24-hour clock all the way back, it's the equivalent of, you know, you and I flying back and forth to mainland Europe from England, you know, every weekend. That's torture on your biology. And so, again, it's something that we don't often think about, but it can have really major impacts on our health. Could you perhaps make up for it with some sort of naps if you sort of slept for just sort of one hour and slip those in every day? It's a very, it's a very, it's a very interesting idea, and it comes on to a even more fundamental question, which is how are we designed to sleep as a species? Now, right now, most of us in developed nations, we sleep in what we call a monophobic pattern, which is where we try to get one long bout of sleep at night, somewhere

between seven to nine hours, hopefully. But if I place an electrode on your head and I measure your brainwave activity, and if I did that for everyone who's listening right now, I would reliably see a drop in your alertness somewhere between about the 1 to 4 p.m. period for most people. It's that afternoon lull that many of us feel. You know, you're in meetings at work in the afternoon, and all of a sudden you see those headbob starting to happen, and you know, you know for a fact what's just happening there. You can't fool anyone. We know that you're you're dipping your beacon to sleep, as it were. Now, many of us think that that's because maybe we had a big lunch. It has nothing to do with lunch. I can prevent you from having lunch and you'll still

have that drop. In other words, there is a physiological, hardwired, pre-programmed reduction in our alertness during the afternoon as if we were designed to not sleep in this monophasic pattern, but to sleep in what we call a biphasic pattern. In other words, one long bout of sleep at night, let's say, you know, six to seven hours, and then a short afternoon nap, very much like the seester cultures around the world. So that could be one way to sleep, but naps have a double, well, naps are a double-edged sword and they have a downside to them. There is a dark side, I should say, to naps. And it's the following. When we are awake, and from the moment both you and I woke up today, a chemical has been building up in our brain. And that chemical is called adenosine.

and the more of that adenosine that builds up, the sleepier we will feel. And adenosine is the sleepiness chemical. It's almost like a sleep pressure. By the way, it's not a mechanical pressure. Don't worry, it's not going to explode because of this pressure of adenosine. It's a chemical pressure. And then, after about 16 hours of being awake, we should feel plenty sleepy enough to be able to fall asleep and then stay asleep soundly across the night.

And then what happens as we sleep is that the brain gets the chance to clear away all of that sleepiness, clear out all of that adenosine, so that we wake up the next morning and we're refreshed, we're restored by our sleep. The danger then with naps is that if you take a nap too late into the day or in the evening, all the nap is too long, it's a little bit like, what would be the analogy? It's a little bit like releasing the valve on a steam cooker. You know, you release some of that health. sleepiness, and that can make it harder for you to fall asleep and then stay asleep at night. Or a better analogy would be, you know, napping too late into the day or too long is a little bit like snacking before your main meal. It just takes the edge of your sleepiness hunger for the main serving of sleep at night. So I think my advice to people would be this. If you don't struggle with sleep and you can nap regularly during the day, then naps are just fine.

try to keep them to maybe 15 or 20 minutes in length and don't nap too late into the afternoon, certainly not into the evening. But if you are struggling with sleep, then our best clinical advice is don't nap during the day. Give yourself the chance to build up all of that sleepiness to sort of set yourself up for the best chances of a good night of sleep. What's the most surprising or significant piece of sleep research to emerge in the past five years? Oh, gosh. I'm desperately biased. I think everything that's coming out on sleep is the most fascinating in all of science.

But I actually think it's probably the striking link that we've now discovered between insufficient sleep and Alzheimer's disease. That evidence has caught light and it is now very, very clear. So the first hints of this happened probably about four or five years ago at an associational level. epidemiological level. What we were finding is that people who were reporting sleeping, sort of less than six hours of sleep, had significantly higher likelihoods of going on to develop Alzheimer's disease. They had significantly higher amounts of the sticky toxic protein associated with Alzheimer's disease called beta amyloid when they were in their later years. And then we also

knew that people who had sleep disorders, people who had insomnia and who had sleep apnea or heavy snoring, that's untreated. Those people also had significantly high risks of multiple forms of dementia, including Alzheimer's disease, which is one form of dementia. So that's simply association. It doesn't prove anything. So correlation then went in search of causation. And what we subsequently found in studies, and we've done some of these studies too, is that if you deprive a human, a healthy human being of sleep for just one night, or you even selectively deprive them of just the deep sleep for one night, there is an immediate escalation in that beta amyloid, that toxic protein linked to Alzheimer's disease, measured either in the

cerebrospinal fluid, in the bloodstream, or even within the brain itself, and we can do that by using special types of brain scans. So that was a causal demonstration that just one night of insufficient sleep will the next day lead to an immediate buildup. in these toxic Alzheimer's proteins. If that then was the case, if a lack of sleep can create the conditions for Alzheimer's disease, then what is the mechanism? How is sleep doing it?

In other words, when we are getting sleep, what is it about sleep that de-escalates our chances of Alzheimer's disease? And a stunning discovery was made a couple of years ago by a scientist called Macon-Nedegarde at the University of Rochester in America. And in mice, what she discovered was that as we go into sleep and during deep sleep, there was a pulsing, cleansing mechanism that kicked into high gear. And it would wash away all of this metabolic detritus that builds up as we're awake. Because rest assured, wakefulness can be considered from a biological

perspective as low-level brain damage. And what she discovered was that sleep was our sanitary cell It's almost as though it's, you know, good night, sleep clean. There's a power cleanse for the brain that happens each and every night. Why is this related to Alzheimer's disease? Because one of the toxic pieces of detritus that she found that the sleep cleansing system was washing away was beta amyloid, the amyloid associated with Alzheimer's disease. Now, I know all of this may sound remarkably depressing or even alarming, which in some ways, you know, it is alarming. But I think there's a silver lining here because what this suggests is that unlike many of the other factors that we know contribute to Alzheimer's disease, that we can't do anything about,

sleep is a modifiable factor. And at my sleep center here in the United States, in Berkeley, and California, we are trying to electrically stimulate the human brain. and particularly in the elderly, and we're trying to see if we can restore back some of that healthy quality of deep sleep. And in doing so, can we salvage aspects of this cleansing system and even salvage aspects of their learning and memory? That's one of our sort of moonshot goals. But what I also find even more exciting is the idea that if this is true, and it really does seem to be proof, sort of positive from the evidence, then what if we can, right now, in dementia research, we are at a model of late-stage treatment. Well, here is something that gives

us hope for a model of mid-life prevention, because it's during sort of mid-life, somewhere between our late 30s, early 40s, when we already start to see the decline of deep sleep happening. So what if we can start to augment human sleep at this mid-life phase? Can I perhaps bend the arrow of Alzheimer's disease risk down on itself and therefore start to decrease the propensity of this vicious disease. Thank you so so much for your time, Matt. Really appreciate it. And hopefully we speak to you again soon.

I look forward to it. And thanks for beaming out this message. You are a sleep ambassador now, Thomas. And I hope you get plenty of it yourself. So thank you for having me. Thank you for listening to this episode of Instant Genius with today's guest, Professor Matt Walker.

If you want to know more about the science of sleep, you can of course check out his upcoming podcast series titled Matt Walker. And you can also hear Matt explain the science of dreaming on the Instant Genius Extra podcast right now. And if that's not enough, you can also find Matt's fantastic article called The New Signs of Sleep

on the BBC Science Focus website. If you've enjoyed this episode, please do leave us a review wherever you're listening. This podcast is sponsored by Name, Audio and Focal. The texture and emotional depth of music can be lost through digital sources or poor signal. Name Audio believes you can have digital precision with analogue warmth.

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