#126 – Matthew Walker, Ph.D.: Sleep and immune function, chronotypes, hygiene tips, and addressing questions about his book

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I guess this week is Matthew Walker. Many of you are probably familiar with Matthew as back In I think April 2019 or so, we released a three part series on sleep and then did a two part follow up of AMAs in June and October of that year. So if you're a listener of this podcast, you've spent a lot of time listening to Matthew Walker. That said, the demand to have Matthew back on has been overwhelming and there's always a lot of stuff to talk about with Matthew. He's such an eloquent speaker on the topic of sleep. We just continue to get a lot of questions on this and so we figured there was no better time and place to do this than here and now. So the interview was actually set up to be only an ama, but one we went very long and also after the fact, Matthew and I felt that some of this topic really ought to be put out there for a more general audience. So what you're about to hear is the obviously the regular episode for all listeners, and it's going to be followed by an AMA for subscribers only. So in this episode we talk about sleep in particular in the Age of COVID what have we learned about sleep through the lens of this pandemic? We also talk about the sleep foundations and the tips that we can use to trigger better sleep. We dive a lot deeper into into the sleep chronotypes and even discuss a test that allows you to identify yours. We talked a little brief discussion about children and nightmares, night terrors and things like that, and then we end the discussion talking about something that I think a lot of people have been asking about, which are some of the errors that readers have pointed out in Matthew's book, why We Sleep. So as a quick refresher on Matthew for those of you who might not know, he's a professor of Neuroscience and Psychology at UC Berkeley and he's the founder and director of the center for Human Sleep Science. Earned his degree in neuroscience from Nottingham University in the UK and his PhD in neurophysiology, also in the UK from medical research Council. He's the author, as I said, of the international bestseller why We Sleep. And he's just an overall awesome guy that I could talk to about sleep and race cars equally. So without further delay, please enjoy my conversation with Matthew Walker. Well Matt, it's awesome to have you back.

It's a delight to be here.

Yeah, yeah. I mean, we talk so often that to put some structure to a discussion in this context will be fun, but there's always so much that we're talking about. At least 50% of it involves sleep. The other 50% seems to involve our other favorite mutual discussion, which we'll try to not talk about today.

But can we talk about motorsport to begin with? No, I'm just kidding.

You sleep it will be exclusively Sleep it shall be. Although I do love the book in the background behind you there. Don't think I can't see that since we last spoke, which was almost a year ago. Obviously the elephant in the room here is Covid, and I'm just wondering if you have seen or have any understanding of the impact that anything to do with COVID has had on sleep. In other words, has the world in which you pay all of your attention, has it been impacted by this?

It does seem to have been impacted and we actually have some decent data. The way it's been impacted is probably at three levels. The amount that people are sleeping, the timing of the sleep, and then finally dreaming. Firstly, in terms of amount, probably one of the earliest reports that I saw was from a sleep tracking company that released data of I think about 68,000 individuals here in the United States. And what they reported was that total sleep time had increased across the entire country by 20% they said, which I struggled with a little bit. But furthermore they broke it down on the basis of each state and what they said was that there was no single state that hadn't increased its total sleep time by 10%. Now those are just reported data from a sleep tracking company and I didn't get the chance to actually look at them. But then two recent peer reviewed papers have actually come out in the same journal, and it's a good journal, Current Biology, that seem to provide support for this. They downscale the amount but they add nuance. So the first paper was a paper published From a group in Europe looking at a collection of folks throughout Europe. Firstly, what they reported was once again, total amount of sleep had increased by 15 minutes. They also found that something called social jet lag had decreased. What is social jet lag? Social jet lag is the difference between the sleep that you're getting during the week versus the weekend. So what typically happens is we don't get enough sleep during the week and then we binge at the weekend and then come Sunday night because we've woken up 10am, 11am on Saturday and Sunday, we have to drag our biological clock back by two or three hours. It's brutal on the clock. It's like flying back and forth from San Francisco to New York every weekend. What they found was that people were going to bed and waking up at much more similar times during the week than they were the weekend. And therefore that difference, that social jet lag difference had decreased, which is beneficial.

It almost feels like it vanished. When you think back to those early days, especially of March and April, where everybody would joke about it, which is what day is it? If you weren't really thinking about it, you didn't know the difference between a Wednesday and a Saturday. They all sort of seemed like the same day, which of course would theoretically squash social jet lag to zero.

Yeah, it bleeds or it sort of softens the boundaries between those two distinct parts of that seven day week. And of course, I think what was happening there was that people didn't have to wake up as early as to go to work. So commutes had been removed for the large part. And then having to wake up even earlier than that so that you could get your kids ready for school and get them away. Those two forces which typically make people wake up earlier than they otherwise would want to. And then of course people were not coming home as late because they didn't have the back end commute. And those two things normally squeeze the amount of time that we have for sleep. Like vice grips in the middle of the night. In other words, modernity with, you know, getting your kids to school and commute times has essentially compressed. People having to leave the house earlier and they come home later, that's been removed. So the opportunity for sleep has actually expanded during the weekday. And that's what they had found too. What was interesting though in that European study is that overall, and I think this gets to the nuance, the quality of sleep that people reported, some of them were reporting worse quality sleep. And I think we'll get to that too.

Sorry, just to ask more about that, Matt, does that mean people felt subjectively more fatigued or they felt that their sleep was more interrupted and that they were waking up more or just having bad dreams? Like what did it mean by subjectively the quality seemed worse?

We don't know which of those three or other options it was. The question is simply what do you feel as though the quality of your sleep was in terms of a question? So this is just subject looking back retrospectively in the rearview mirror last night, what was the quality of your sleep? And I think what you're touching on is something really important because I believe that when we actually finally do look at the data, it's going to be more complex and there's going to be at least two different clouds of data that we see. There's going to be one proportion, one cloud of people for whom sleep actually has increased and the quality of their sleep is actually better. I think what we'll find is that there's another cloud of data for whom sleep has actually become shorter and worse. Why is that? Because they've either lost their job, they may lose their job, or just in general, they have a great deal of anxiety, of course, because of COVID So I don't think the story is quite as simple as we're seeing right now. But that's sort of what we've seen in terms of the amount of sleep. It does seem to have changed overall, but the timing of sleep has also changed. If you look at these studies, on average, people were actually going to bed about 30 minutes later and waking up about 50 minutes later the next morning. So I think this is finally the revenge of the night owls. That because modernity favors morning larks, or we call morning types that, it's designed for morning types and it has. We chastise the night owls as being lazy. Well, why don't you get to bed earlier? Because biologically they can't. That's their chronotype. And finally, now with COVID and the relaxation of these work rules, night owls are being allowed to be much more owl like and sleeping in harmony with their chronotype rather than trying to work against their chronotype. So not just the amount of sleep has changed, but the timing of when we're sleeping has also changed as well.

Is that seasonally adjusted, Matt? So as we go from winter to spring to summer in the Northern hemisphere, do we tend to see movement of bedtimes and wake up times? I know with my kids, for example, we definitely see it because of the light. It's Easier to get them to bed earlier in the winter than it is the summer. But is that true with adults also?

It is true with adults. You do see that seasonal shift as long as there's sufficient exposure to light. But if you're an individual who essentially you wake up under your electric lights in the morning, then you go to work and it's constantly lit in that work environment, then you drive home and you're not getting much daylight exposure, the influence with which the outside world impacts your sleep schedule is therefore diluted and lessened. So you have to be exposed. And your kids are a great example of that because they're outdoors playing all day at school, they're given outdoor activities. So you will see some of that too. But in general, yes, you're absolutely right. That will shift on the basis of seasons, depending also on your latitude. I mean, you know, if you're living close to the equator, you won't see that get expanded the further you go north and south.

But these findings are basically above and beyond what you would see seasonally is what I'm understanding.

That's right.

So another thing I want to ask you about on Covid, when I think back to March in particular, but probably into April, I was having dreams that were unusual even by my standards. I'm one of those people that tends to have vivid dreams most nights. I can usually even remember them at least as soon as I wake up. But I think I would say they were even more heightened. Has the literature commented on that at all?

It has, and I think there is too much subjective inbound that we've had. That confirms what you're describing too. And I believe when more data comes out, that's what will happen. We will hear and find that dreaming has increased as a consequence of COVID Why is that? I think there's probably at least two different reasons. First, it comes back to timing of sleep. And maybe we can at some point sort of go over the standard sleep schedule.

Well, let's do it now. I think we should assume that maybe people haven't necessarily listened to our first episode where you describe the cycle. So we'll let people fast forward a few minutes. But for those who need a primer, maybe go through stages one through four in REM and the cyclicality of it.

So humans and most mammals, at least land dwelling mammals, have two principal types of sleep. On the one hand, we have non rapid eye movement sleep or non REM sleep for short. And non REM sleep has been further subdivided into four separate stages that are unimaginatively called stages one through four because we're a creative bunch, as in sleep research. But on the other hand, by the way, for stages one through four of deep sleep, they increase in their depth of sleep. So stages three and four are those really deep stages of non REM sleep. And on your sleep trackers that will be described as deep sleep. Stages one and two of non REM sleep are typically what you classify as light non REM sleep. On the other hand, we have rapid eye movement sleep or REM sleep. And REM sleep is typically associated with dreaming. Now, it turns out that we dream in many different stages of sleep, but the dreams that we all think of that are narrative, emotionally filled, bizarre, hallucinogenic, those principally come from rapid eye movement sleep. So we have these two types of sleep, non REM and rem, and they will play out in this beautiful battle for brain domination throughout the night. And that cerebral war is going to be won and lost every 90 minutes and then replayed every 90 minutes to create the standard cycling 90 minute architecture of the sleep cycle that then just repeats throughout the night. But coming onto your question of, and this is why it's relevant, the ratio of non REM to rem within each 90 minute cycle as we move across the night changes. And what I mean by this is in the first half of the night, the majority of those 90 minute cycles are going to be comprised of lots of deep non REM sleep. Stages 3 and 4, non REM sleep and very little REM sleep. But as you push through to the second half of the night now the brain has a shift in its taste preference for what it wants to feast on at the finger buffet of sleep stages and instead now it actually wants to consume much more rapid eye movement sleep and it's lost its appetite for deep non REM sleep. So in the second half of the night, the majority of those 90 minute cycles are comprised much more of rapid eye movement sleep. And this has implications in lots of different ways. And one of them comes back to Covid. If people are naturally now, on average going to bed a little bit later, but certainly sleeping in significantly later in the morning, what's going on, it means that they're now sleeping further into that REM sleep rich window of the night. And we spoke about REM sleep being associated with the most vivid hallucinogenic narrative dreams that we experience. In other words, I think the first reason that people are dreaming more during COVID is because they're sleeping in a little bit later and therefore just probabilistically from a statistical point of view, you're much more likely to be in a dream state and have significantly more dream cycles as a consequence. So I think that's the first reason.

That makes sense, population wise. I know for me that's almost not going to be the answer because my bedtime shifted paradoxically earlier on both ends. In other words, I started going to bed earlier and waking up even earlier, which may have just been simply anxiety. But I mean, there was a period there where I could not sleep past 5am and part of that is I have a lot of patience and people. My team is mostly on the east coast, so getting up at 4:30, which is 7:30, their time just seemed like the normal way to go about business. But I almost wonder, I don't know enough about dreaming and I apologize because I bet we did talk about this two years ago when we did our first go around, which was probably nearly two years ago. But is there a component of this that is also just a way to purge negative emotion or stress in some way? And is that potentially also a part of this equation?

That's why I love our time together and chatting. That's exactly the second reason. And that's the reason why even though your sleep schedule didn't change, you still were dreaming more. Because one of the principal functions of rapid eye movement sleep that we now have understood is that it seems to provide a form of overnight therapy, that REM sleep is emotional first aid. And it's during REM sleep that we take the emotional concerns and even sometimes in extreme examples, some of the traumatic events that we've been experiencing. And REM sleep almost acts like a nocturnal soothing balm and it tries to take the sharp edges off those difficult experiences so that when you come back the next day, you don't feel necessarily as emotional as you did about those events the day before. So in other words, it's not time that heals all wounds. It's actually time during REM sleep and dreaming that provides this emotional convalescence. And what we also know is that sleep is responsive. It's not a fixed system necessarily. It's what we call homeostatically regulated, but also homeostatically reflexive. What I mean by that word salad is that if something happens during the day that requires sleep and a specific stage of sleep, then sleep will respond by giving the brain a little bit more of that sleep to deal with whatever happened during the day. And a good example here is learning and memory. We've done some of these studies where we'll have people all of a sudden go into three or four hours of really int of textbook learning, and the next night we see an increase above and beyond their baseline in the amount of sleep that's needed for the fixation of those memories. If we do a skill learning task like a sports task, it's a different type of sleep that's needed. We see a homeostatic response from sleep that following night to try and lock in those new skilled memories. And it's the same for emotional experiences. If you've upped your quotient of emotionally difficult experiences, sleep can respond with greater amounts of rapid eye movement sleep or dream sleep to try to help solve those emotional challenges. So I think that's the second reason why even if you're not changing your sleep, you can still be dreaming more. Does that sort of help reconcile that?

It does. And it also brings to the front of my mind another issue which I do. I know I'm not going to be the only one admitting this, which is I found myself more reflexively reaching for a glass of wine during, and frankly I think probably more so to this day than I would have historically. Right. I think I probably consume four or five glasses of wine a week right now, Matt, whereas historically it would have been four or five glasses a month. And I would say during the height of sort of my anxiety around some of the aspects of COVID I was probably drinking a glass to sometimes two every single night. And I just know from my own tracking of sleep, which is primarily based on the aura which I need to disclose. I'm both an investor in aura and an advisor to them. So please understand and take anything I say about aura with a grain of salt. But I think the aura provides a very good stream of data on metrics around sleep, particularly time in bed or time sleeping, and the variables that drive some of the interpretations of stages, namely heart rate, heart rate variability, temperature and respiratory rate. And without exception, Matt, every time I drink alcohol, especially if it's going to hit two drinks in a night, every one of those variables moves in the wrong direction. Yeah, heart rate variability gets crushed. Resting heart rate goes up by 10, if not 20, 25%. Respiratory rate is up two breaths per minute, and core body temperature is up half a degree. That, coupled with what I remember of our first discussion, which is alcohol disproportionately impacts negatively rem, creates kind of an ironic situation, which is I'm probably numbing a little bit of my anxiety with alcohol, which is impairing my ability to have REM sleep. Which is paradoxically exactly the medicine I need.

Yeah, that's exactly the interpretation I would offer. And then it becomes a self fulfilling prophecy. So you're right. Firstly, you know, one of the problems with alcohol is that it's a sedative. And what most people think of as the benefit of a nightcap for your sleep is not really a benefit. Yes, you quote unquote. Well, I'll say you lose consciousness faster when you put yourself in bed. It's hard to say that you're going into naturalistic sleep. Your sleep becomes more fragmented because the alcohol will actually stimulate the fight or flight branch of the nervous system. It also releases wake promoting chemicals. That's why you wake up more frequently. And then the third part is alcohol will decrease the amount of REM sleep that you get, particularly in the middle, towards the later hours. And of course, as you said though, what's happening very understandably is that you're trying to find a way to manage your anxiety.

And by the way, as a parent, I don't even know how much of it is about anxiety around coronavirus as it is anxiety around kids or other things that are the response to coronavirus. As you said, your job again, your kids are going crazy. Being home in front of Zoom 24 7. I mean, it's. Sometimes you don't even realize what it is that you're reaching for that drink for. But you know, my wife and I will constantly joke like, is it 5 o' clock yet? Is it 5 o' clock yet?

It's got to be 5 o' clock somewhere in the world, right?

Exactly. And it's weird because neither of us are the type of people who we could easily go two months without having a drink and not notice. So there's just been something particularly challenging about the last six months that I think have led to just more frequently that type of behavior. And I, I say that not trying to be too judgmental of myself, just as an observation, but I'm guessing I'm not the only one that's gone through this.

Yeah, and I have a huge degree of sympathy for that situation. Everyone has this cabin fever and then you put together three kids. And as you mentioned, there too there is this self fulfilling prophecy where if you're downscaling the amount of REM sleep that you get at night with alcohol, you may not be getting the necessary emotional benefit that you need to de risk the emotional experiences and the anxiety that's building up. So then the next day the anxiety is not dealt with, it's overlaid and then added to by the following day. And so you're feeling even more anxious the following night. And then you find yourself reaching for another glass of wine, which then takes away the REM sleep once again. And so goes the spiral of escalation. So again, I'm not trying to be at all judgmental. I'm just a scientist. I'm not here to be puritanical about life. Life is to be lived to a degree and I don't want to tell anyone how to live their life. I think what we're just trying to do here is describe the consequences of these things on sleep so that people can be informed and make their own life choices as to what they would like to do.

Now, Matt, one of the things I have the luxury of doing is looking at the aura data of of all of my patients who wear an OURA ring and who are in our portal. And I will say this. When I couple that ability with the ability to speak with them, I've noticed not all people are the same. I really think there are some people for whom alcohol does not seem to have that negative effect. Like for example, in me, one drink doesn't really seem to have a negative effect provided it's around 6pm and I'm going to bed at 9pm but two drinks does have the effect. I've seen patients for whom two drinks has no effect. And when I've had this discussion with them about, hey, you know, really, from a scientific standpoint, it would be great if you drank less for reasons X, Y and Z. Their counter argument is, well, the relief that comes from the alcohol, the true release of stress may justify it. And I guess I've come to realize that every one of these things has to be taken on a case by case basis. But when it pertains to sleep, would you agree with potentially my observation that people are not all identical in this regard as well?

100%. And I think, in fact, if you do some of these genetic testing companies out there, they will describe to you whether you're a fast metabolizer of alcohol. There's a genetic basis to it. It's the same with caffeine. So you're completely right that there is an average adult that we will typically speak about when we speak about large scale, be it epidemiological studies, which we're both not necessarily a fan of, or even any studies. And we offer recommendations. This is for your average adult, but everyone is unique in that sense. And so there absolutely will be some people, one side of the distribution, who don't show that response to alcohol because maybe they're a fast metabolizer and they have a drink at 7pm and by the time it's their turn on their sleep schedule to be in the position to start receiving and chowing down on REM sleep from that buffet, most of the aldehydes and the ketones are now long gone and not impacting their sleep, which are the metabolic consequences of alcohol degradation. And those are the things that seem to impact your REM sleep. So I believe that there are definitely that cluster of people and then equally there are folks on the other side who can have a glass of wine with a late lunch and it still could crush their REM sleep. I think the take home here is that we should all go to the pub in the morning and that way the alcohol is out of our system by the evening. But let's not make that statement.

Just stop drinking by noon and we think you're going to be fine. So the other thing on Covid, if we can spend just another minute on this, is I really want to understand from you what you think the richest sort of data are with respect to sleep and either innate or probably adaptive immunity. So one of the things that I've thought a lot about in the past few months is the impact of nutrition, the impact of cortisol. In fact, we wrote a piece on that a few weeks ago and there was actually some very elegant experimentation looking at the impact of, of hypercorticolemia on the adaptive immune response to five common cold viruses. I think it's common sense that sleep improves immune function. But can we say anything specifically or more to the point, have we learned anything new with respect to Covid on that front?

I don't think we have the data quite yet on sleep and Covid. And I should also say for this conversation in general, I really want to be mindful of feeding into the general anxiety that's out there in the world that we're experiencing right now. And we'll speak probably a lot about the consequences and the impact of insufficient sleep. So I just kind of want to maybe throw a sticky on the wall and just kind of be upfront and be sympathetic to that before I speak about what we do know. So we don't have any data yet directly regarding a lack of sleep and your vulnerability to Covid or if you are infected, the severity of progression. But we definitely know firstly that there is a very intimate association between your sleep health and your immune health. We know from a study, gosh, one of the Classic studies in Archives of General Medicine that individuals who report getting less than seven hours of sleep a night are almost three times more likely to become infected by the rhinovirus, which is the common cold, relative to those who sleep more than seven hours. So there is some vulnerability risk there. We know from a study, perhaps that's relevant here, there was a study, I think it was in over 70,000 women, and it was a prospective study, so a little bit better. And what they found is that women who were sleeping five hours or less were 70% more likely to go on to develop pneumonia, which is a component risk that we understand in the equation of COVID We also know from animal studies that this is just not associational, it's actually causal. There was a fascinating study where they were selectively depriving mice of sleep, and particularly REM sleep. And what they found is that when they were exposed to malaria, the mice that were deprived of sleep were far more likely to die as a consequence of that malaria exposure than the well rested mice. So there is something about survival risk there. And then we also know from classic studies, and this to me is perhaps the most interesting one for Covid, that if you're not getting sufficient sleep in the week before you get your flu shot, you end up producing less than 50% of the normal antibody response, therefore rendering that flu vaccination significantly less effective. And we have no idea, of course, right now what the ultimate vaccine is going to be, and therefore we have no idea about its relationship with sleep. However, I think we do need to be prospectively looking at this when the vaccine comes out and tracking sleep, because if your sleep in the days before you get your Covid vaccination determines whether or not it's successful, we should know that and we should be smart about it. What about a future where, you know, you're upcoming for your appointment and your sleep hasn't been great? And I say, look, doesn't look like you've been getting perfect sleep. Let's just wait a few more days. I've booked three more appointments next week. Select the one that you want and we'll look for a future when you're better slept and we'll have a significantly higher, you know, success rate. I don't think that's coming anytime soon, but I'm just sort of, you know, this is beer and nuts talk, since we're speaking about alcohol, as to what could be possible. But I do feel as though we need to understand what is the relationship between sleep and your immune response to that vaccine. Once that Vaccine is there. So does that paint a little bit of. I know it's nascent because we don't really have direct data yet, but I think there's enough data to tell us we should certainly be studying it.

Well, first of all, the sleep immunization. I mean, I've never heard that before. That's super cool. I'm literally scribbling a bunch of things down as you say that, because that's also the easiest question to study. That's a really easy study to do. And the implications of that are profound. I get asked, I don't know, somewhere between 46 and 50 times a day. Peter, when's the vaccine going to be ready? When's the vaccine going to be ready? What's your take on the vaccine? And, and my take on this is nuanced. I won't go into it now, but I think part of my take on Covid vaccines is going to be. I think it's going to take a little longer than we think. I think it's going to probably be not quite as safe as we think, meaning not something you just want to indiscriminately give to everybody. In other words, I think it's like any vaccine is going to have some risk and it's certainly possible that at least some of those vaccines, potentially really efficacious ones, may come with side effects that are undesirable and therefore we'll have to think about who gets them.

By the way, you said plural there. Do you think there will be multiple vaccines on offer and multiple vaccines of different types?

I do. I mean, that's. My intuition is. I think there will be several approaches. I think there probably will be specific ones that are looking just at rna. There'll be, you know, sort of surface ones. There'll be live. I don't, I don't know if there'll be a live attenuated one. I mean, we're working, you know, when I say we, like I'm having anything to do with it, but I mean, I think the royalty. Yeah, yeah. I think the scientific community is working their way up from the, you know, the lowest hanging fruit and going all the way up. And that says, of course, nothing about monoclonal antibodies and other therapies. But I guess my bigger point is it's not like on a certain day we will have enough vaccines to give everybody. Right. That's certainly not going to be the case. So even if you just think about this through a very US centric view and say, well, when will the United States have enough vaccines to appropriately cover its citizens that could be years away. And then it means, well, as you identify the populations that are most at risk, which be presumably the people you want to vaccinate first, my guess is healthcare providers would be atop that list. But also the people that are most vulnerable from a underlying condition perspective, anything you can do that could increase the efficacy of that vaccination by 50%. I mean, if it turns out that the SARS CoV2 virus has a behavior that is comparable to influenza with respect to this property, I mean, that's, you know, you don't get many opportunities to 2x something anyway. I just hope that somewhere out there somebody in these phase two studies, because we're just basically in the, you know, we're at the time of this recording, at least the phase two studies are being launched. It would really be wonderful if somebody could do a subgroup analysis on how many soluble antibodies are you getting? You know, what type of T cell response are you getting? And can we at least retrospectively look at the sleep quality going into that, if not prospectively?

And if anybody out there are doing those studies, it's very simple to do. You know, we could do it with sleep trackers, but there's paper and pencil things that we could do. Feel free to reach out to me, and I'd love to sort of just provide some simple tools to do that. But what was interesting in that immunization study, they looked at around, I think it was somewhere between, you know, 11 to 14 days after the flu shot, and they just saw this, you know, catastrophic reduction in antibody response. But then they did something smart. They said, well, maybe it's just delayed. Maybe they do get to that level and it just takes them a little longer. So sleep is just slowing the. The true peak of that antibody response. But they kept assessing them, you know, 20 to 30 days later, and they just still saw nothing. So it really did seem to be that it had just blunted it and you'd lost that chance and it wasn't coming back. Wow.

Yeah, that's. That's. If I learn nothing more in the next whatever period of time we're speaking, Matt, that I got my money's worth on that little factoid.

And if you don't learn anything more in the next coming time, then I have failed utterly miserably. But there's my challenge.

Let's pivot away from COVID and kind of get back into some of the Sleep foundation stuff and some of the background questions. So a little less than a year ago we sat down and did an ama. I don't remember how long we sat down. What I do remember is it was at the end of the day of a day of exhausting but exhilarating racing in Bakersfield, California. We were both beat and I think we, we, we sort of cried uncle after about two hours. So we didn't get through all of the questions. And I think that's part of the stuff I want to talk about today. Maybe we can kind of go back and, and revisit some of the, you know, you gave us a pretty good primer on REM and non rem. Anything else you want to kind of go back and revisit before we jump into some of these other things that you didn't already cover earlier today just to get people kind of back to the foundational level of the architecture of sleep.

I think we did a pretty good job. I know you spoke a little bit about that variability of response to alcohol and I just want to respect that variability. Once again, I said that There is a 90 minute cycle and for the average adult it seems to be about 90 minutes. But that isn't necessarily consistent, by the way. It's, you know, for some people it's shorter, for some people it's longer. And even for different species, it's very, very different. So we humans, we have a 90 minute cycle on average. But you know, other species, birds for example, their sleep cycle from non REM to REM can be maybe just 2 or 3 minutes much shorter. Non REM to REM SLEEP CYCLE so it's very perplexing. We actually don't really understand what determines the length of your sleep cycle across phylogeny across different species. The best guesstimate that we have right now is that it has something to do with the relative mass size of your brain. It has a weaker correlation with body mass. But for the most part, the larger your brain mass, the longer your sleep schedule and your relative brain mass relative to the rest of you, the organism. But it's one of those strange things, by the way, we also don't know. I know, I'm not really answering. You're essentially saying, can I clarify anything? And I'm now just telling you things that we don't understand. But I hope that's okay too, which is we have no idea why sleep plays out in the way in which it does that I described, which is that you get most of your deep sleep in the first half of the night and most of your REM sleep in the second half of the night. What I mean by that is we understand what determines why you get your deep sleep early in the night, which is largely determined by how long you've been awake and a little bit on the basis of your circadian rhythm, whereas REM sleep is much, strongly, much more powerfully determined by the circadian time of night. But we still don't understand what the function of that skewed seesaw balance actually is. So we understand the factors that drive that different distribution, but we don't understand the evolutionary functional reasons as to why Mother Nature drives it in that way. But overall, I think we've done a pretty good job of hopefully outlining what sleep is, how it's structured, and its timing.

I remember you saying that REM is even more under circadian control. Is that actually the same as saying that REM occurs more often in the, as you said, the latter part of the day, or does it speak more towards the ability to reset that clock? And if my question makes sense, great. If not, I'll pivot to a different question that I hope gets at the same thing.

So REM sleep is less determined by how long you've been awake during the day. That is much more deterministic of how much deep sleep and how deep that deep sleep is going to be. And that's what sort of almost forces the serving of a plate of deep non REM sleep up in the first couple of cycles.

So, just to be clear, Matt, and sorry to interrupt you, does that mean then that deep sleep is more a function of how much adenosine you've accumulated, how much melatonin you've accumulated, and how much cortisol you've suppressed? Those three things factor more into your ability to generate lots of deep sleep.

Probably a little bit less. So the middle one, which is melatonin, some of the last one, which is cortisol, higher cortisol typically means less deep sleep, but very much so. The first one, which is adenosine. And to explain what adenosine is, from the moment everyone listening woke up this morning, a chemical started building up in your brain called adenosine. And the longer that you're awake, the longer the amount of clock time that your brain has been awake, the more adenosine builds up. And adenosine is a chemical that produces what we call sleep pressure. And the more of that sleep pressure, in other words, think of it as sleepiness, the longer that you've been awake, typically the sleepier that you feel. What you're feeling is the weight of that chemical pressure of Adenosine. Now it's not a mechanical pressure in your brain, don't worry. It's a chemical pressure that's signaling sleepiness. The more of that adenosine that there is in the brain, the more of that deep sleep that you typically get. You're absolutely right.

That makes sense. Now as you describe it as that pressure, the question now comes down to one of napping, which we did touch on in our previous episode, but I want to revisit it. Lots of times patients come to me and say, Peter, you have no Idea what a 20 minute nap does for me between 2 and 4 o' clock in the afternoon. And my historical response to that has been, you know, gosh, you really shouldn't need a nap. I mean, if you're sleeping correctly, isn't that actually a negative thing because it's depleting some of that adenosine based pressure. And wouldn't you be better off letting the pressure cooker cook, driving you into a deeper sleep when you first take your sleep? So what are your thoughts on that type of a nap, that sort of short 20 minute, late afternoon, pre dinner nap?

Naps really are a double edged sword. And we've done lots of studies where we use naps to study the functions of sleep and we see benefits from naps. Even naps as short as 17 minutes can produce learning and memory benefits. So there does seem to be some, some enhancement that you get and you can see that from cardiovascular benefits as well. The downside of naps is that it can take away just what you described, which is sleep pressure. And so the typical recommendation that we have is the following. If you are struggling with sleep at night, avoid naps during the day. Because what you want to do, if you are already having problems, either falling asleep, which is what we call sleep onset insomnia, or you can fall asleep but you can't stay asleep, which is what we call sleep maintenance. Insomnia. You want to build up as much sleep pressure, as much sleepiness as you possibly can during the day. In fact, sometimes what we do for patients with insomnia is something called bedtime restriction, where we'll even tell them, I know that you're not sleeping enough. And paradoxically, I'm going to tell you that you should go to bed even later. And they think, well that's stupid, I should be going to bed earlier, shouldn't I? Not necessarily, because what we want to do is elongate the amount of wakefulness that you've been building up even more than is normal. So you build up an even greater sleep pressure. And as a consequence, yes, you may only have a six hour sleep window that we now give you on this sleep restriction therapy, which is part of cbti. But that six hours may be a very constant solid sleep. And that's, we believe, much better than you lying in bed for eight hours and tossing and turning for two of them and only sleeping six hours. So in both scenarios, you still get sleep six hours. But in the kind of clinical scenario, and by the way, I'm not a clinical doctor, I'm just a scientific researcher, so I'm just describing what happens in cbti, at least with that delayed bedtime. It's a nice consistent quality of sleep, because quality of sleep matters just as much as quantity of sleep. So I'm going a little bit off topic, but to bring it back, if you are struggling with your sleep at night, do not nap during the day. And the pressure cooker analogy is beautiful. Keep building up all of that healthy sleepiness pressure, because when you nap, it's like having the valve on the cooker open up and you just release some of that healthy sleepiness. And now when it comes time to go to bed, you're not going to feel as sleepy anymore. However, on the flip side, if you are not struggling with your sleep and you can nap regularly during the day, the advice is naps can be just fine. Because in fact, if you take a step back from an evolutionary perspective and you study hunter gatherer tribes whose way of life hasn't changed for thousands of years, they don't necessarily sleep the way that we do in modernity. In fact, particularly during the summer months, they will typically have an afternoon nap right in the time zone that you just described. And this is the very much the Mediterranean siesta like behavior. And in fact, if I stick an electrode on both of our heads throughout the day and I monitor our physiological brainwave activity, it'll stick much better to.

My head, by the way, than yours.

Well, yeah, right now, especially because I've got this terrible Covid, which I look like I should be out of Buck Rogers and anybody who remembers that television show. But anyway, what we will see is that somewhere between about 2 to 4pm Both you and I will have this kind of drop in our physiological alertness, in our physiological level of brain activity. In other words, as if as a species, we're almost pre programmed to have this enforced diploma in our alertness. And so many people see this, you know, in the afternoon meetings, around the boardroom table or wherever you sort of get these ugly head nods that start to happen. It's not people listening to good music. It's just that people have this sort of they're falling asleep, they're falling prey to this, what seems to be a genetically hardwired pre programmed drop in our alertness. As if maybe we should be what's called biphasically sleeping as a species at times during the year, rather than monophasically sleeping, which is how we do in most first world nations. In other words, one single bout of sleep at night versus two bouts of sleep, which is how those hunter gatherer tribes sleep, especially during the summer.

And so Matt, would they sleep long enough in that two to four window that they would get a full 90 minutes, say, and get through a full cycle? And then if so, did that mean when they did their nighttime sleep, presumably they would stay up later and get maybe six hours in the evening instead of, you know, because people always talk about how. Well hunter gatherer studies have always suggested that, you know, seven and a half to nine is the species required amount of sleep on average. But you're saying it was potentially broken into two chunks. Was that afternoon daytime chunk or daylight chunk, call it about 90 minutes.

No, it wasn't. It was actually typically shorter than that on that basis. But you're right, they typically are not sleeping. What we currently recommend for monophasic sleep, which is the average adult should get somewhere between seven to nine hours. That's the recommended range that we all provide. But what they would typically do is they would maybe sleep just six, six and a half hours at night and then they would make the rest up and they would get into that exact same sort of territory by way of the nap. So they would take it in these two chunks. Now I should note this is very different to something else that's been described in the literature, which is first sleep and second sleep. That activity does seem to have occurred during our historical past. It seemed to have emerged in the sort of Dickensian era. That was different though. That was where people would sleep for the first four hours, then they would wake up in the middle of the night, they would, you know, write, they would drink, they would play music, they would make love, and then they would go back for another four hours of sleep. Did that happen? Yes, it seems to have, based on historical writings. But is that the way our physiology and our circadian rhythms are designed? No, it doesn't seem to be. There's usually one study that's cited that suggests maybe we should do that, but. But overall the Physiology that we know of for human beings doesn't seem to suggest that that was more sociologically driven rather than biologically driven. Biologically, we may be biphasic, but very differently, according to this hunter gatherer sort of tribe hypothesis. By the way, the other thing that's interesting in those hunter gatherers, and it comes on to what I think we described before, which is this concept of midnight. Most of us don't think of, of what the term means, but in those individuals it means what the word states, which is it's the middle of the night for them, midnight, because they usually go to bed maybe two hours after sundown and they're asleep, you know, by let's say 9:00pm in, in the evening or 8:30 and then they're awake, you know, just a little bit before dawn. In fact, what's interesting, and maybe we'll get onto this in later discussions, or we won't, but what seems to wake them up is not necessarily daylight. It's the change in temperature because there's a rise in temperature that seems to happen before daylight starts to break. And it seems to be, it's the temperature change that they are much more buckled to in terms of regulation of their sleep wake rhythm. And so the way in which the structure of their sleep biphasic is different to ours in modernity and the timing of their sleep is different to some of our timing. You know, for many people midnight is the time that you think, well, I should just check Facebook one last time or, you know, send my last text. That's what midnight means. But normally for a couple of thousand years or hundreds of thousands of years, it probably meant that was the middle of your solar cycle and it was the middle of your sleep cycle.

I'm glad I'm closer to our ancestors. If I could go to bed at 8 o' clock every night and wake up at 4, that is a perfect night of sleep for me. And by the way, you may have already mentioned this, but just to close the loop on it, do we have every indication that our ancestors also had 90 minute cycles, or do we believe that there was a period in our evolution as Homo sapiens when our cycle was longer or shorter? I accept the fact that obviously when our brains were smaller, when we were pre hominoid, it might have been different.

I don't think we know of that data yet. I think most of those studies have used wristwatch sleep tracking rather than actually taking PSGs out there into the field.

How many people are there left in the field to study? I mean, I know that in Australia there are some aboriginal cultures that still allow us that opportunity, but I mean, in Africa, are there others as well?

Yeah, there's the san in. I think that's how you pronounce it in Namibia, there's a couple of cultures in South America. So there are probably about four or five different cultures that have been studied. Hunter gatherer tribes. But we don't actually know if the sleep cycle is similar. My suspicion is that it is. But if we want to reverse and go into the time capsule further, what seems to have happened, if you use different primates as the best kind of data reversal of our evolutionary timeline. There was something about the transition of Homo sapiens from tree to ground which increased the amount of REM sleep that we were getting dramatically. And in fact, if you look at our sleep amounts relative to other primates, our non REM sleep amounts are human beings, you know, Homo sapiens. Somewhere in that distribution, we're pretty similar. But in terms of our REM sleep as a primate, we are a complete standout. We have almost double the amount of REM sleep that any other primate has. And so I think, and in the book, I sort of did some, lots of hand waving and pontificating about this. I wrote a book, and in some of those chapters I sort of speak about what was the cause of that and what did it allow. And I think one of the benefits was, you know, emotional intelligence. It wasn't iq, it was EQ that REM sleep also allowed us to develop. But there was something that happened as we moved from the trees to the ground, because orangutans, other species, they will sleep up in trees. In fact, they will build a bed every night up in a tree. Imagine, you know, if you said to your kids every night you're going to have to unpack a piece of IKEA bed furniture and build it before you go to sleep. Every single night, you're going to have to do that. Well, that's what some of these primates do. Every night, they build a new bed. But anyway, the idea is that I don't know about the sleep cycle, but during our evolutionary past, as we transition down to terra firma, we increased. There was something about that. And I think it has to do with the paralysis that happens during REM sleep, which is obviously, if, if you're living 20, 30, 50, 100ft up in the trees and you're lying on a branch and all of a sudden you lose all muscle tone, which is what happens when you go into REM sleep. Bad Things are probably going to happen. You're probably going to be popped out of the gene pool quite quickly that way. So when we became safe on the ground from a sheer Newtonian physics standpoint, then all of a sudden, REM sleep blossoms, and with it, I think, a whole constellation of new benefits for the hominid species.

I just can't resist making one comment about motorsport. I'm sorry, Matt. Well, not sorry for you, because you're.

Going to love it.

I'm sorry to all the other listeners. I was listening to our favorite F1 podcast last week, and they were talking about the golden age of F1, which was, of course, the 80s. And someone made a wisecrack that the chief aerodynamicist for the McLaren team in 1986 was Sir Isaac Newton. And I just couldn't stop laughing. I was like, that is so great. And for the listener, what that really means is back in 86 was really before you had any ground effects in cars, and so there was no aerodynamics. It was basically the only thing that held the car on the ground was its own mass and the force of gravity. But those cars were beasts, right?

Yeah, they were absolute beasts. I mean, and before that, Colin Chapman at Lotus tried some of this stuff. If you look at some of the Herbrane stuff that they were doing, these crazy aerofoils that sat about 4 or 5ft above the car on these stanchions, and you never quite knew, I think, as the driver, whether it was going to force you down and stick you to the road more, or whether the next report that you made was that you were about 30,000ft above the Arizona desert and you've sort of essentially gained some degree of altitude. But, yeah, I think Adrian Newey probably has a slightly better grasp on things now.

Yeah, well, look, it's not called the drive for nothing, so every once in a while we are going to have to just.

I'm sorry, folks. Sorry no more.

All right, so look, we have a pretty good handle on this stuff now, Matt, and on previous episodes, obviously, we went into some pretty good depth on tricks, tips, et cetera. Inside our practice, we have a whole sleep hygiene protocol, and we sort of run patients through it relatively early, especially if they're having any sleep issues. But. But do you mind just sort of going through where you are now and how you think about this? And again, I'll caveat this by saying you're not a sleep physician, so it is not your practice to be out there treating any one individual with respect to their sleep.

That's right.

But Also, you're infinitely more qualified than virtually anybody to help people start to think through what the parameters are that factor into sleep. And that's the way we kind of explain it, which is, look, here are these five or six, six levers of sleep. And here's how you could move each of them in your control. But I kind of want to hear how you think of it.

Yeah. So I think in our past episodes we've gone through sort of the five main sort of sleep hygiene tips. And I'll just quickly go through them here because we've dealt with them before, which is regularity, going to bed at the same time, waking up at the same time, getting lots of darkness at night because we are a dark deprived society. And I actually think I've done a bad job of describing to the public the importance of the opposite, which is making sure you get daylight during the first half of the day. I think that's just as important then temperature, we've spoken about that a little bit. You need to get cool to get to sleep. And it's the reason that you will always find it easier to fall asleep in a room that's too cold than too hot. You shouldn't stay in bed awake. That trains your brain to be triggered by your bed and force you awake because you have a learned association. So if you've been awake for 20 minutes, then get up, go and do something else and only come back to bed when you're sleepy is the general rule. And then finally trying to avoid alcohol and caffeine in the afternoon and alcohol in the evenings, as we've said. So those are the sort of typical tips. But I think if I were to add a few others, the other one that's absolutely critical that I probably haven't espoused enough is a wind down routine. Because many people in society expect sleep to be like a light switch, that we should just jump into bed and we should just turn off the light and the brain should do something similar and go straight into sleep. Sleep as a physiological process, if you study it, it, it's just not like that. Sleep is much more like trying to land a plane. It takes time to gradually descend down onto that hard foundation of this thing that we call a stable night of sleep. So give yourself some wind down opportunity time, build it into your routine. For some people it's 15 minutes, others it's 30 minutes. Light stretches, meditation, putting all of your phones and your gadgets away, staying clear of any inbound in the last 30 minutes, whatever it takes, set it up and then maintain it, because if you have kids, you'll know all about this. You know, you have a routine for the kids and you've got to try and stick to it. If you break the routine, bad things usually happen. With sleep, we're the same as adults. There's no difference. So I think that's the first thing I would say the second probably tweak is if you are struggling with sleep, remove all clock faces from your bedroom. It's not going to help you to know that it's now 2:35am in the morning and you've still not been able to fall asleep. It's only going to trigger more anxiety. And there's been a nice study here from UC Berkeley, not from my center, but from another sleep researcher, Alison Harvey, who looked at this in people who were poor sleepers with insomnia. Removing clock faces can certainly help. The next thing I would say is that try to keep, of course, all of your technology outside of the bedroom, and if you can, don't make it the first thing that you check in the morning. Because for most of us, the first thing that we do when we wake up is that we swipe right and this flood of anxiety just washes onto us like a tsunami. And that's problematic not just because it's a bad way to start your day, but because you train your brain in this Pavlovian way that every morning, as you're tucking yourself into bed at night, every morning, what's coming to you when you wake up is this jag of what we call anticipatory anxiety. And it lightens your sleep throughout the night because of that expectation. So try to avoid that if you absolutely have to. And again, try not to be puritanical. Take your phone into the bedroom. One of the other problems is that it causes what we call sleep procrastination, which is that you're sitting there in bed, you've got your device, and you think, well, I'll just check Amazon and order that thing. I'll just check Facebook and I'll just send that last email. And you look up and now it's 40 minutes later. The rule of thumb that a friend, a colleague of mine, Michael Gradner, said, I love this. If you're going to have your phone in your bedroom, the rule is that you can only use it if you're standing up. And after standing up for about 5 or 10 minutes of phone use, you just think, I just want to sit down. I just want to get into bed. And at that point the rule is you've got to put your phone away. So those would be sort of three additional things that I would advise that can really help.

I like that a lot. I would actually add, just from a personal standpoint, I've maybe three months ago instituted a little policy for myself that I've really enjoyed, which is not looking at my phone for an hour when I wake up.

Yes.

Luckily, I don't sleep with my phone in my room, so that's not an issue. But it used to certainly be first thing I'd go and grab when I got up. And if I get up at 5, I won't look at it till usually after 6am and that's interesting. I didn't realize that the effect that that could have on my brain as I'm coming into consciousness, knowing that I'm not going to be flooded with information, especially the type of information I don't like, which is generally all the information on my phone.

Yeah, I'll just stick two additional pins in that. The first is I think everyone has had this experience in the extreme, which is where, you know, you've got to wake up the next day for an interview or you've got to wake up for a flight that you have to catch. You know for a fact that firstly, your sleep is going to be shallow, it's not going to be particularly deep, and secondly, you almost wake up two minutes before the alarm because you're that on edge. Well, imagine a diluted version of that. But every single day, that's what bringing your phone into the bedroom and opening it up first thing is all about. The second thing I would say is you're right and set manageable goals. I really enjoy the work of a guy called BJ Fogg, who's a researcher at Stanford who looks at behavioral change. And it's all about incremental. So if you're trying to get someone to floss their teeth for the first time for dental hygiene, don't say, okay, here's how you floss. You need to floss before you go to bed. You say, all you're allowed to do for the first week is floss your front two teeth and you cannot do any more. That's it. And then we say, then add two more teeth for the next week and then two more. The same with sleep. If you are accustomed to doing this with your phone, which is so understandable for all of the pressures that we understand from society and social media, start by saying, I'm going to give myself five minutes. I'm going to firstly not check my phone. I'm just going to wake up, brush my teeth and make whatever drink that I have in the morning. And when I sit down, that's when I am gifted the opportunity to look at my phone and then try to push it to 10 minutes and then try to see if you can get changed, have your shower, wash yourself up, whatever you do in the morning, and only then open up your phone and keep pushing it longer and longer. Make it a manageable goal. Otherwise, don't set yourself up for failure, do it for success.

Yeah, I think the same advice is great for something like meditation, where for many people saying, hey, why don't you commit to 20 minutes of meditation a day? I mean, that's almost impossible out of the gate. But if it's, hey, meditate every day, and if you do a three minute meditation, you're better off doing three minutes a day than 20 minute once a week. I think it's the same sort of idea, which I agree. I think it becomes a lot easier.

The last thing I would say is that none of these tips that we've spoken about, which are typically sleep hygiene tips, are going to work if you actually have a sleep disorder. So the analogy here again from colleagues, like if I'm an athletic sports coach and I'm giving you all of these tips for improving your performance, but you've got a broken ankle, none of them are going to make any difference to your performance until we actually get you to a doctor and fix the broken ankle. It's the same with a sleep disorder. If you have, you know, insomnia or if you have sleep apnea. None of these things that I've been talking about are going to help you. If you suspect that you have either one of those, definitely go and see your doctor, see if you can get some kind of sleep intervention.

Matt, last time we sat down, you talked briefly about the sleep chronotypes. And I've found this interesting for basically two reasons. One is just observing probably a migration in my own daughter's chronotype, which is as she's getting older, she's sleeping in longer in the mornings and going to bed later and later. And I know that as she gets closer and closer to being a teenager, that's probably going to increase, but also just more cognizant, I think, of other people. You alluded to it briefly earlier, which is like there are just people who are going to go to bed later and wake up later. And it doesn't mean that there's anything wrong with that or there's anything wrong with the reverse, which is people who go to bed early and wake up really early. So kind of wondering if there's a way to actually know what chronotype you are beyond just observation. Because is it possible that the observation is not your optimal state? In other words, if you have somebody who's sleeping a certain way because their job is imposing it, but it's not the way that they're ideally meant to do it. Let me give a better example. A student in college could easily drift into a later chronotype because everybody in their dorm room is, even though they may actually be more suited to be earlier. So how can one figure this out?

So there are genetic tests that will give you a stronger sense of your chronotype. So chronotype simply means. Yeah. Are you a morning person, are you an evening person? Or are you somewhere in between? And somewhere between 25 to 30% of the population are morning types, 25 to 30% are evening types, and then the rest of us are somewhere in between. Sleep science has then gone a little bit further. We split it into five categories sometimes, which is extreme morning types, morning types, middle evening types and extreme evening types. We know that it is under strong genetic control for two reasons. First, there is a significant degree of heritability. So if you are a morning type, it's more than likely that one or both of your parents were mourning types. Secondly, we now know that there are a collection of genesis that will determine to a degree your chronotype. And this is why companies like 23andMe will tell you what type you are, or they will give you a probabilistic estimation of what type you are. Last count, I think, from data from 23andMe and there's data from the UK Biobank, there's about nine different genes that we know of right now that will contribute to your chronotype. Most of them are what we call clock genes. This refers to the fact that these genes control the rhythm of your circadian cycle. Now, those genes don't control necessarily the size of your circadian rhythm, in other words, how kind of strongly active and awake you are during the day and how deeply sort of down you go at night. These genes do something different. These genes control when that sinusoidal wave of your circadian cycle arrives on the clock face. What I mean by that is if you have a certain type of gene complement that makes you a morning type, your activation peak, your peak alertness is going to arrive earlier in the day and your awesome downstroke of your circadian rhythm will arrive earlier in the evening. Whereas if you have a different combination of these gene composites, then you could be an evening type. In other words, your circadian rhythm looks very similar in its sinusoidal pattern. But when the peak and the trough of that circadian rhythm arrive on the 24 hour clock face is very different to a morning type. So we know that there is a complement of genes that you are given at birth that will determine on average, once you're an adult, are you a morning type or are you an evening type? What you alluded to, however, for your daughter was something different, which is that no matter what chronotype you are, that innate chronotype rhythm that you have gifted by your genes will change as you develop from a young child to an adolescent teen, to an adult to an older adult. In other words, you go from being much more of a morning type. When you're a kid, even though you want to stay awake longer, you're found on the couch and you're carried to bed and you're fast asleep to then being a teen where your chronotype fast forwards in time. And this is a problem for early school start times where you're putting kids to bed at 9pm and saying you've got to go to bed because you have to wake up at 5:00 in the morning to catch a 5:30 bus for a 7:15 start time. Well, there's no point in saying that it's not their fault that they're now in bed and it's 10:30, an hour and a half later and they can't fall asleep as a 15 year old because their chronotype has moved forward in time. They want to go to bed later and wake up later. Nothing they can do about it. It's biology. And then once they become an adult, it starts to shuttle back a little bit once they become sort of, you know, moderate age 30 or 40. And then as we start to get older, we regress. That's why in Florida there's something called the early bird special where people are going out for dinner at, you know, 4:00pm or 5:00pm because their chronotype has regressed back and they're in bed by, you know, 8pm so there are genetic tests to come back to your question. However, you don't need to do a genetic test to get close to understanding what you are. There is a pencil and paper method that sleep scientists have developed and you can Google it, it's called the MEQ test. And maybe I'll send you the link and we can put it in the show notes.

Yeah, we'll put it in the show notes.

And it's a very simple link that you just click. And it's a test. It probably takes about five or six minutes to fill out. And it's called the MEQ test, the Morning Eveningness Questionnaire test. And you go through, you answer a list of questions and at the end you add up your score and it will tell you what flavor of chronotype you are. And what's nice is that then they've pattern matched this test and validated it against these gene, these genetic tests. And there's a pretty good correlation. It's not too far off. So this is the poor man's version of the 23andMe test, if you want it. And we'll do a link in the show notes and you can take it. And that's a website, a cheaper way, a pencil and paper method or an online method.

So the bigger question is, Matt, what do we do with this information? Right? I mean you've, I think we did talk about this previously at one point that you have a couple who have different chronotypes. That can be really difficult. They're going to bed and waking up at different times. You've already alluded to the problem of children who are, I think, being subjected to potentially too much early school, when in reality they probably would do better with later school. Is this the kind of thing that should factor into decisions people make about when they pick classes in college? I mean, it seems like this seems to be one of those things where there might be a bunch of people that go through life kind of miserable when they don't have control over their schedule as opposed to knowing this. And so would knowing this by itself provide a benefit to folks?

I think it would. I think it would explain a lot about why you struggle so much where other people seem to be just these energizer bunnies and they've even got time to go to the gym for an hour before they sit down at their office desk at 7am in the morning and you're still on your fourth cup of coffee, desperately trying to wake up and you're struggling to make it in by 7:15, having woken up 20 minutes before. And I think the second thing that it helps with is just realizing that you're not culpable. It's sort of non mea culpa. It's not your fault. It's. You can understand that this is genetic because a lot of night Owls have gone throughout life being chastised and thinking, well, if only I could get my act together and get to bed earlier and stop being what people tell me I am, which is slothful or lazy, you know, I could hold down a better job or. And again, I think society needs to be much more understanding of it and also then modifying itself in response to accommodate it. And neither of those things I see in full serving scoop sizes in society right now. And that should change. And I think Covid is interesting because if there's some positive upside to it, it may have given us the chance for people to understand how much better they can sleep when they're closer in harmony with their own chronotype rather than trying to work against it. Because when you fight biology you normally lose and the way you know you've lost is often through disease and sickness. And I think there is a version of that going on here. I also think it can sometimes explain incorrect insomnia. Often the. Often I'll hear someone tell me if I'm sort of out in the public, they'll say, well, I suffer from insomnia. I get into bed and I can't fall asleep and I'm wide awake for the first hour and a half and I need to take some sleeping pills and then I'll, I'll say, you know, first thing, I'm not a doctor, but let me just ask you a question. If you are on a desert island with no responsibilities, nobody foot to wake up for, nothing to do, and you could just sleep whenever you want and get up whenever you want, what time would you normally go to bed? And they would say, well, I would actually like to go to bed at midnight and wake up around 8 o' clock in the morning in truth. But I have to get up from my job, I have to wake up at 6, so I'm getting in bed at 10. But I still have this terrible insomnia. And I say, well, you know, I don't know this, but it's possible that what you could have is not insomnia but a mismatch between your chronotype and your working life schedule. And you may want to explore some of this. And there's a test, an MEQ test, and I tell them about this and then go and speak to your doctor. So that's the second implication that I think comes from the question that you asked about how it impacts society. Once you know it, what do we do about it and what should we be doing about it? Those are some of the ramifications I.

Think there's a question that actually came in that I think a lot of parents might be able to relate to and this might be outside of your area of expertise because I know you're not a clinician per se and if so, if the answer is we don't know, that's fine. The parents ask. We have a six year old and they've basically experienced sleep terrors. But the parents noticed something which is that exhaustion triggers the terrors. So when their child is actually well rested, he doesn't get them. And they're always trying to implement great sleep hygiene. So I think what the question is here, is there any empirical observation to support this or is that just a nuance of their child? Child?

I think there is good reason to explain why it happens. Firstly, night terrors are typically where people wake up and it's more common in children with just this terrible sense of dread and fear. And kid is almost inconsolable at that stage that they're crying. But what's interesting is that even when you know you have one of these night terrors as an adult, if you were to ask people what was, you think, well, they were having a horrific dream. But if you ask someone you know, what was going through your mind just before you woke up, they typically say, you know, nothing much, I don't remember anything. And in part it's because many of these night terror events seem to happen from deep non rem sleep, dreamless sleep, rather than rapid eye movement sleep. That's the first thing. Second thing is that we don't really understand too much about the brain mechanisms because in part it's not a good thing to study. You know, the way we can study some of these events in the brain is that we put you into a brain scanner and we start scanning you while you're having, you know, lots of these events. For example, whilst you're trying to make memories and we try to have you learn 100 different memories and we scan you 100 times and we build up a map of what successful memory formation looks like. That's how we do these studies. But you can't stick a child in a scanner for eight hours and with just one event hope to capture it and get a good signal signal. So we actually don't really understand much about the real time brain dynamics. But the reason I bring up non REM sleep is that just as we spoke about before, when we are spending more time awake or we've had essentially sort of supercharged or extended wakefulness when we go to bed at night, we typically then have a homeostatic increase in the amount of deep sleep. So what could be happening here? And again, this is just hand waving. But one explanation would be that when the child is exhausted, maybe they haven't been sleeping as well, maybe they missed their nap, maybe they've been awake for typically longer than they would do otherwise. They're probably going to go into deep non REM sleep in a more intense fashion or with greater amounts of deep sleep duration, which is therefore going to mean that the probabilistic likelihood of them having one of these night terrors is increased as a consequence. So that's sort of from a scientific perspective, but you're absolutely right. I am not a sleep science, a pediatric sleep scientist. I am not an md. I would refer anyone who has issues or questions about infant sleep or pediatric child sleep to one of two people. The first is Dr. Craig Canapari. And maybe I can send you guys a link and you can link to his website. He is just fantastic. He is the director of pediatric sleep at Yale Medical School. He's written a great book that parents can read about sleep and infants and children. You could read it in an afternoon. It's just brilliant. It's a lovely book. He's a great guy. He's got a fantastic website with tons of resources. I wish I could keep my website like he does. Curates it beautifully. So, Craig canopari, both with Cs, and then the other person is Jodi Mindell, who is kind of like the God. You know, there's godfathers and godmothers of research. She's sort of one of the godmothers of child and infant sleep out there in the world. So I will send you a link there to include in the show notes. If you have any questions about child or infant sleep, one of those two individuals is more than likely going to have an answer. They are brilliant.

I want to pivot to another topic, Matt, which is I know you're sort of working on a second edition to your book, is that right? Right?

That's right. That's correct. Yeah.

And I know that over the past, I don't know, nine months or so, there's been some discussion of errors in the first edition of the book. And anyone who's written anything knows that that's pretty normal. Back when I used to blog a lot, I don't think I could get through a blog post without making one mistake. And sometimes the mistakes were literally just mistakes of fact. Like I cited the wrong paper or hyperlink to the Wrong thing. And sometimes they were mistakes of interpretation. I sort of read a paper out of context or things like that. But can you give us a sense of where you are in the process of revising this first edition into a second edition and what you've learned about any mistakes you've made and how you could quantify the.

Yeah, that's right. So since publication in 2017, a number of readers have reached out or notified me of errors in the book. And when that happens, when they've reached out to me personally, I take what they've said. I go to the book, I have a look at it, I will cross reference it, I will see if it's an error. If it's an identified error, I have a document that was cataloguing all of those errors, knowing I would then at some point, continuing to check with the publisher, when the time is right, we would then publish a second edition which would make those corrections. So in total now, and we've now completed that exercise, there have been 13 errors in the book that we've identified that required correction. And I have to say that that's been very difficult for me to learn of those errors. And it, it remains a disappointment to me.

Now, I was actually looking at the book the other day because you probably don't remember this, but you wrote a lovely inscription in my book for my son because he, when he was really young, loved all the moon pig.

That's right, Yeah, I remember it.

And as we're getting ready to move, you know, we're starting to slowly pack some stuff up. So the book is. It's not the thickest book on the planet, but it's, you know, it's 300 to 300. It's over 300 pages. Do you have a sense of how much data has made its way into that book in terms of how many statements or assertions have you made a fact?

Yeah, I have. In all of this, I've gone back and I haven't tried to catalog everyone but the estimate. It's probably a little over a thousand facts, I think, which I know gives some relativity to that statement. But nevertheless, it just remains very vexing to me to have identified those errors.

Does my categorization make sense? I mean, do you want to go through any of those errors and talk about them in terms of. Do you want to go through like, I misinterpreted or I literally just made a mistake and I cited the wrong paper? I mean, how do you want to describe some of those errors?

Yeah, I can describe sort of the Seared into my brain at this point. Near tattooed, I would say. One example is that the book described an association between sleep and cardiovascular disease, and it said that the study looked at over half a million individuals. Now, that study did evaluate over half a million in terms of its collection of the data. But for that analysis, that specific analysis, it wasn't over a half a million individuals that were involved in the analysis. It was actually 474,684 individuals, which is not over half a million. So that was an example of an error that was in the book. I think another example of an error or a misjudgment was that in the opening introduction of the book, sort of the general intro, what I'd stated is that short sleep can double your risk of cancer. That was not specific writing, and I think it was poor writing on my behalf. Short sleep does not double your risk of all forms of cancer. And you can probably tell me better. At least at last count, I understood there to be probably over 100 different major forms of cancer. And short sleep is not associated with every single one of those. And certainly it's not associated with the doubling of a risk of every single one of those. So what I should have said is that short sleep is associated with a doubling of a risk of specific forms of cancer, of which it is. And examples would be ovarian cancer or lung cancer. So that's a correction that needed to be made. And I think that was poor judgment on my behalf. Another example that was brought up was this really interesting relationship between sleep deprivation and depression. So I wrote there was many pages in the book devoted to this, which is in a subset of patients with depression. If we deprive them of sleep for one night, we get this really interesting antidepressant benefit where it helps them. And in fact, we've gone on to do MRI studies where we've tried to understand what is going on in the brain to produce this antidepressant benefit, this paradoxical antidepressant benefit. So we've tried to contribute to that work. And I discussed that work in the book, too. That wasn't the issue. What I stated in the book there was that somewhere between 30 to 40% of patients with depression will respond to sleep deprivation. Now, two years after the book was published, there's been a meta analysis that's now shown that it's not 30 to 40%. In fact, in prospective studies, it's 45%. And so we've been able to correct that in the book. I would just Note one other very clear set of errors. The book, at one point, again, speaking about sleep loss and cardiovascular disease, spoke about a study in over 4,000 individuals looking at cardiovascular disease. And in fact, that was true. The study looked at, it was 4,652 individuals in that study. But when I described the data regarding cardiovascular disease, it was only a subset of individuals. And I had said it was over 4,000 individuals. It wasn't. It was actually only 2,282 individuals that were analyzed for that analysis I described. So that was a clear error. And then the second part of that study that was also erroneously described in the book was that I spoke about sleep loss, or short sleep, I should say, being associated with an increased risk of cardiac arrests. And they did not state cardiac arrests in that paper. What they were stating the outcome measure was cardiac events, not cardiac arrests. And you need to be specific, because what they were describing there in cardiac events was not just myocardial infarction, heart attacks. It also included other things like angina pectoris that required coronary bypass. So once again, there was an error in the description of the outcome measure. So it wasn't cardiac arrests, it was cardiac events. And that's also been changed, too. So those are some of the errors that have been corrected in the book. And there have also been some misgivings, I think, about the interpretation of certain data, and I can speak about those, too. But those, I think are some examples. Does that give you some context? It's not just citing the wrong paper. There were just very clear errors regarding numbers of subjects or the specific outcome variable.

Yep. Yep, that definitely makes sense. And by the way, this is near and dear to my heart for selfish reasons. Right. Is in the process of writing a book and having a fact checker, I'm still reeling in the fact that you only had 13 errors. Because admittedly, the first draft of my book is about twice as long as yours, and maybe it has more facts in it, but there's one analyst who works for me, part of my research team, who is the fact checker for the book, and his name is Vin. And I think Vin is finding like 13 errors per page in my book. I doubt that, but a lot of them are interpretive errors as well. Well, it's like, well, there's another way you could read this paper. And you said this, but it could have been this. So what were some of those interpretive errors that you think you've made?

One of the interpretive errors that people have had is regarding long sleep and its association with mortality risk. So one of the things that is clear in the literature and that the book is very clear about, is that there is not unlike REM sleep, actually, there is not a linear relationship between sleep and mortality risk. It's not that, you know, the more and more you get, the better and better things are, the lower your mortality risk. That is true up to a point, but once you get to sort of nine hours and beyond, your mortality risk stops going down and it actually starts to go up again. And this has led to the misinterpretation that, you know, long sleep is bad for you. Long sleep will kill you. Long sleep is associated with a faster death. Now, at the time in the book, I think the general modus operandi in the sleep research field was that it was because those studies, which were large epidemiological studies, had not measured all of the different disease outcomes in those studies. And what was happening was the following. When we get sick, the main thing that we want to do is curl up in bed and go to sleep. Why? It comes back to sleep in immune health, because when you are sick, you release a whole collection of immune factors, particularly the cytokines that are sleep inducing. In other words, it's a homeostatic mechanism for you to get into the brain state and body state that the body knows is the best form of health insurance policy that it's got, which is this thing called sleep. So the idea for long sleep was that these patients were probably already sick and they were having sickness that wasn't being measured and factored into these analyses that we weren't quantifying. And it was that additional sickness that was missing from the analyses but was still present that was forcing those people to sleep longer than they would normally otherwise. They were trying to sleep themselves well, but whatever disease that they had was still too powerful for this thing called sleep. And they still died. So it artificially looked like long sleep was associated with a quicker death, when in fact it could have been that long sleep was the thing that was desperately trying to save them, but it failed. That was the interpretation of in the book. That was the interpretation at the time. And I think that is still true. But there's been a second interpretation that's come onto the scene that again has a good example of how I've changed. I've updated my mental iOS, my operating system with a new belief, which is something different, which is that long sleep is also associated with poor quality sleep. And poor quality sleep, independent of length of sleep, is itself associated with mortality risk. So in other words, the lower and lower the quality of your sleep, the higher your risk of death. Also, we know that when people are not sleeping well, they typically try to stay in bed longer to try and get more sleep because the quality of their sleep is so bad. And so once again, what's happening here now is that poor quality of sleep is masquerading as long sleep, which is associated with higher risk of death. But it's not really long sleep. It's a thing that's causing those people to stay in bed and look like they're sleeping longer, which is the poor quality of sleep. And so that was, I think, something else that people had raised about the book that I had not mentioned and has now also been rectified in the book and mentioned. That's, I think, one example of an interpretation issue. I think another example is lack of clarity in my writing. One of the statements that I made, which is actually true, which is not an error, is that the World Health Organization had classified any form of nighttime shift work as a probable carcinogenic. They made that declaration in 2007 originally. Then they re examined the data and in 2019 they reasserted that same statement. If you want to get nerdy and technical, it's actually a Class 2A carcinogen, a probable carcinogen. The issue here is that it was actually some people googled this and said, no, what I'm finding is that it's actually the International Agency for Research on Cancer, the IARC that made that statement. Matt, it's not the World Health Organization. So that's an error. You got that wrong. But it turns out that the iarc, the International Agency for Research on Cancer, is a part of the World Health Organization. And if you look at the little sort of info card that was published in that press briefing, you'll see the little icon of the World Health Organization in the top corner of that. So that's not people's fault. That's natural for them to say, you made an error. Mat it's what I should have said in the book is not just that the World Health Organization, I should have said, it's the iarc, which is part of the World Health Organization, which together made the statement of it being a carcinogen. So that's another place where I've been able to, you know, there's a long form blog that was also published. It's over 8,000 words. People can find it on WordPress that describes not only all of the errors that are there in the book that we've just discussed and all of the others, the corrections that will be made. But I also go through any of the misgivings or the sort of the changes in interpretation that people have had regarding what I discuss in the book, and I walk them through a collection of detailed science to a level that I wasn't able to do in the book. And it's pretty nerdy science, but it's there because I felt as though not only in response to this did I want to make all of the changes in the book, because I should just note I see it as a critical part of good scholarly conduct that you correct any errors that are identified. And I always hold myself to that standard. And that's what's happening in the book right now. I've sent all of those changes to the publisher, and they should be coming out in a new second edition of the book. But the second thing I wanted to do was sort of go into detail and clarify some of these interpretations and at least give you all of the additional science supporting why I offered those specific interpretations in the book that I did above and beyond simply describing the errors.

So obviously, for people who don't necessarily want to wait for the second edition to come out. The long blog post you wrote, presumably we can easily link to that.

That's right.

Okay, so that'll be in the show notes as well.

Yeah, it's still. Nevertheless, it's remained difficult. You mentioned you and other authors, and I said about Michael Pollan's book Caffeine, and when I first started to realize some of these errors. And Michael, there's a collection of. It's strange, there's a collection of Bermuda Triangle of writers here in Berkeley. There's sort of Michael Pollan, there's Michael Lewis, the collection of us know each other and we'll occasionally out for dinner. And Michael's become really good, and he's been very helpful to me over the years. And I wrote to him and said, you know, I need to sort of speak with you. I didn't tell him what was happening. And I said, can I take you out for dinner? And what's nice about Michael, because he's a food writer, if I try to book a restaurant, you know, at a certain time, they'll say, oh, I'm sorry, we're full. And then Michael calls up and he gets a table. So I took him out for dinner. And early on in the dinner, I reached over, you know, very quietly, because I was ashamed. And I sort of said to him, look, Michael, that I need some help Because I've identified these, you know, errors in the book. And I was hoping that the only witness to that statement at that point would be my salad that was sitting underneath me. And I was expecting to, you know, see what he said. And, you know, he just seemed to. He just brushed it off. He just said, you know what? Well, gosh, for my probably most scientific book, which is Omnivore's Dilemma, I don't think it was until the third edition until I ironed out all of the errors. And I have to say for about an hour during that meal, I felt some degree of lowered anxiety about it. And then probably at least another hour later after leaving the restaurant, I went back to just feeling very vexed and upset about it. So anyway, that's the correction. Thanks for letting me speak about that, by the way, and thanks for bringing that up. That's very good of you. Thanks.

If anything, it's made me not want to write my book.

Oh, I hope not. We all need it. We all want it. Write that book.

We'll see. Well, Matt, I'm sorry we didn't get to do this in person, but the next one we will do in person.

Let's make sure.

Yeah, yeah, we're doing the next one in person regardless. Even if we have to sit in masks across from other each.

Well, you said that people have a love hate relationship with sleep. A like dislike relationship. I'll be left to see about your listeners as to whether they want me back. I think my general personality is kind of like a dislike. Dislike. There is no like a dislike. I think some people have described my personality as the best prophylactic known to man. So yeah, if you will have me back and if your listeners will have me back, then I would be delighted. And if that's the case, guaranteed, we do it in person.

All right, Matt, thanks so much.

Thank you again for having me. Really appreciate it. Take care, Peter.

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