How To Improve Your Sleep And Why You Should | Professor Matthew Walker | Audio Only

Matthew Walker 0:00 Sleep is the single most effective thing that you can do to reset your brain and body health each and every day. Sleep is, on the basis of all of the scientific evidence, it is the elixir of life. It is the Swiss Army knife of health, and if you use this sweet spot of seven to nine hours, there's a very simple truth, which is that the shorter your sleep, the shorter your life. Short sleep predicts all-cause mortality.

Dr. Rangan Chatterjee 0:29 Hi, my name is Rangan Chatterjee. Welcome to Feel Better, Live More. [upbeat music] Hello, I hope you are all doing well. Today's episode is all about one of the most important pillars of health, our sleep. Now, improving the quality of our sleep is arguably the single most effective thing that we can do to reset our brains and recharge our bodies, yet many of us simply are not getting enough. Now, when we talk about sleep, we need to be thinking about the length of our sleep, but also the quality. In today's episode, I am delighted to welcome back the world-leading sleep researcher, Professor Matthew Walker. Now, Matthew is author of the international bestseller Why We Sleep, and he's Professor of Neuroscience and Psychology at the University of California, and he is a fountain of knowledge when it comes to all things sleep. Now, longtime listeners will know that this is Matthew's second appearance on my podcast. My last conversation with him back on episode 70 is still one of the most downloaded and shared episodes to date. If you have not heard it yet, I would strongly advise that you go back and have a listen after you've heard today's show. There are so many golden nuggets in that first conversation. Now, today's conversation with Matthew moves into areas that we did not cover last time. You may recall that a few months back I asked my podcast listeners to let me know what further questions they would ideally like me to put to Matthew on a future podcast, and the response was phenomenal. So many questions you had for Matthew, and in today's episode, I put those questions to him. Unfortunately, it was impossible to get through every question, but I have tried my best to cover as many as possible. We cover how grabbing an extra 15 minutes of sleep a day will have benefits for our overall healthspan. We cover polyphasic sleep, unbroken sleep, and why lying awake in bed for long periods of time can affect our ability to sleep in the future. Matthew also shares some fascinating and dramatic changes that have occurred in the way we sleep and dream following the coronavirus pandemic, and why it's allowed what Matthew calls the revenge of the night owls. We also delve into a type of sleep called REM sleep, and how it is one of the best forms of therapy. Our brains can literally re-wire negative memories when we sleep. And finally, we cover sleep trackers, caffeine, and how sleep impacts our immunity. This really is a fascinating conversation full of fresh insights and actionable tips that we can all put into practice immediately. I hope you enjoy listening. Now, onto my conversation with the one and only Professor Matthew Walker. [upbeat music] Yeah, I, I remember really well our last conversation in the bowels of Penguin a few years ago now.

Matthew Walker 3:44 [laughs] Yeah, we were, um... It was in the, um, sort of the sub-basement walk-down. Um, I think it's, it's at the level where usually n- sort of nuclear bunker operations happen. But, uh, we were deep in the bowels of, uh, Penguin Random House, but it was a very special time. Um, I loved that time with, with you, and, um, just felt like speaking with, um, a remarkably insightful, intelligent friend who I, I just could resonate with. Um, and it was empathetic, empathic. It was great.

Dr. Rangan Chatterjee 4:15 Yeah, me too, man. I really remember it, re- remember it very, very well. And, um, you know, we, we had both just had our books out at the time, our first books, and, uh-

Matthew Walker 4:24 [laughs] Yeah

Dr. Rangan Chatterjee 4:25 Well, and on that, your first book has become a global juggernaut-

Matthew Walker 4:32 [laughs]

Dr. Rangan Chatterjee 4:32 ... of a book. Uh, a- and with good reason. It's, it's jam-packed full of information. For people who are listening to this and coming across you for the first time, would highly encourage you check out Matt's book, um, Why We Sleep, and also check out the first conversation I did with you, because it is full of facts, full of all kinds of insightful information about sleep. But my thought where we might start, for people who've not heard that conversation, you said in that conversation that sleep needs a better PR job on it, right? We need s-

Matthew Walker 5:07 [laughs]

Dr. Rangan Chatterjee 5:07 We need better PR on sleep, and so I thought-

Matthew Walker 5:09 Yeah

Dr. Rangan Chatterjee 5:09 ... maybe the place to start would be, why should we care about sleep?

Matthew Walker 5:16 Well, you're right. I think sleep is the neglected stepsister in the health conversation of today, and it remains so, unfortunately. Why should we care? We should care because sleep is the single most effective thing that you can do to reset your brain and body health each and every day. Sleep is, on the basis of all of the scientific evidence, it is the elixir of life. Um, it is the Swiss Army knife of health, and I think the, the decimation of sleep throughout industrialized nations is having a very clear and significant impact on our health and our wellness. Um, in fact, just to sort of give it in the most blunt terms, if you use this sweet spot of seven to nine hours, which we'll come onto, uh, there's a very simple truth, which is that the shorter your sleep, the shorter your life. Short sleep predicts all-cause mortality. But to me, I think, Rangan, what's more important is that investing in sleep, and it really should... You- most people right now think of sleep as a cost. You know, how can I sleep less 'cause I sort of want to be awake more and do more? And I see sleep as the opposite. I see sleep as an investment, and it's an investment not just in your lifespan, but it's an investment in something you care about so critically, and I do, which is your healthspan. It's not just your lifespan. And both of those, sleep, you know, sleep is almost like the tide that raises all of the health boats. And I think it's wonderful that people think about these individual silos of health, your cardiovascular health, your metabolic health, your mental health. But what's remarkable is that you can sort of, you know, focus on each one of those separately if you want, but there is this Archimedes lever. There is this one thing that if you improve it, all of the other health boats rise on that singular tide of sufficient sleep. That's why I think we should care about it and care about it very passionately.

Dr. Rangan Chatterjee 7:29 How much are you sleeping these days?

Matthew Walker 7:32 So, um, I could pull out my phone and look at my Oura Ring. I think last night it was, um, seven hours and 58 minutes. Um, but I was in bed for, um, eight hours and 35 minutes, and I think this is a really important point, not about... Let's not focus about the duration right now. People often hear folks like me say, "Okay, how much sleep do we need?" And the response is somewhere between seven to nine hours of sleep a night. That's what seems to maintain health. Once you get below seven hours, we can measure objective impairments in your brain and your body. But then people think, "Well, seven hours of sleep, so I'm okay to go to bed at 11:00 and wake up at 6:00." That's actually not true because for you to get seven hours of sleep, you normally have to be in bed for at least eight hours, and the reason is something called sleep efficiency. So let's say that I'm in bed for eight hours. My, if my sleep efficiency is 100%, which is completely abnormal, that would mean that for all of that time I'm in bed, I'm asleep. Now, if you're healthy and you're sort of, um, not sleep-deprived, you will have a sleep efficiency of somewhere between 85 to 95%. So 85% is our cutoff for good sleep in terms of sleep efficiency, 85%. So if you're healthy and you've got a good sleep efficiency of 85%, to get a minimum of seven hours of sleep, if you do the calculation, you'll need to be in bed somewhere close to eight hours and 13 minutes. So I think one of the other essential parts of this is sleep, what I call sleep opportunity. You need to give yourself the right opportunity to then get the appropriate amount, the appropriate duration. So when I say seven hours is the, is the minimum, please don't think that that's seven hours of opportunity time. It's going to be much closer to eight hours to get that minimum of seven hours. Does that help, Rangan?

Dr. Rangan Chatterjee 9:47 Yeah, yeah, yeah. Really, really useful. And, and I think making that point right at the start of our conversation is, is so useful, Matt, because people want to squeeze it in and go, they might be starting to prioritize it and go, "Yeah, I need to get seven hours," but they'll often think about that seven hours from entering the bedroom and-

Matthew Walker 10:08 [laughs]

Dr. Rangan Chatterjee 10:08 ... leaving it in the morning. But you-

Matthew Walker 10:10 Yeah

Dr. Rangan Chatterjee 10:10 ... you beautifully explained why that's not the case. And, and Matt, the, the format for today was gonna be, um, a bit different from last time. There was so much interest in our conversation last time. I think it is still the top or the, in the top two of all of my episodes ever in terms of-

Matthew Walker 10:28 My goodness

Dr. Rangan Chatterjee 10:28 ... of, of how many times they've been listened to, and I think that's because of, A, the content, but also the, the clear manner in which you deliver it. But there's a huge interest in sleep, and so we went out to my audience for some questions that they wanted answering from you, and-

Matthew Walker 10:44 Mm

Dr. Rangan Chatterjee 10:44 ... I've compiled a lot of them in a document. There was a lot of similarity, and I thought what we might do today is just go through a lot of the questions that my listeners really would like, uh, answered if possible. I- is that gonna be okay with you?

Matthew Walker 10:59 Lovely. Yeah. That sounds great. Fingers on buzzers, no conferring, questions start at 10:00. [laughs]

Dr. Rangan Chatterjee 11:04 E- exactly. And this one, it's not the s- that's not the first question, but I think it comes in here really nicely.

Dr. Rangan Chatterjee 11:10 Someone's actually said about length of sleep, "I think it's totally unrealistic to get seven to nine hours sleep a night unless you are a teenager." Okay, so that's interesting that someone feels that it's unrealistic for them.

Matthew Walker 11:23 Mm.

Dr. Rangan Chatterjee 11:23 And the follow-up question was, "Is it okay to sleep for three hours, be awake for an hour, and have three more?" So there's a general point here about whether-

Matthew Walker 11:32 Mm

Dr. Rangan Chatterjee 11:32 ... our sleep should be unbroken or whether it can be polyphasic.

Matthew Walker 11:37 Yeah, I'll take the first question. I think it's so understandable when people are struggling with sleep, uh, and they're having sleep difficulties or they'll... And I don't know which of these two, um, it is for this, uh, f- for this, um, person, but, or it's the fact that life just doesn't seem as though it will allow or permit you the absolute human civil right, which is getting sufficient sleep. But I think just to come onto the, the first part of that, if you are someone who is struggling with sleep and- I would s- stop focusing on this idea of, you know, the seven to nine hours. That's only going to make matters worse. Start with incremental changes, and firstly ask yourself why is it that you don't feel as though you are capable of getting that amount of sleep? Let's set aside the idea that it's just your schedule that prevents that. Let's come back to it being something that's biological. The first thing I would say is please go and see your doctor, um, and ask about help with sleep. My suspicion is that it could be something along the lines of insomnia, where you're not able to either fall asleep or you can fall asleep but you can't stay asleep. Um, you don't have to look to medication. Uh, I think this is one of the big fallacies that we have in medicine with sleep right now, um, where we're medicating people with sort of classic sedative sleep medication. There is an alternative that is just as effective as sleeping pills in the short term but is much more effective long term, and it doesn't come with the harmful side effects of sleeping pills, and that is something called cognitive behavioral therapy for insomnia, or CBTI. And if you just go onto the NHS website and you, um, search for CBTI or you search for insomnia, you'll get some great information. That type of therapy will start to help you regain your confidence in the statement that seven to nine hours actually is possible. You know, unless you're starting to move into your later life stages where sleep becomes difficult, you know, up to, you know, ages 50 or even 60, getting seven to nine hours of sleep a night should not be impossible. It, it is certainly a possibility. Um, but when you are struggling with insomnia, you lose confidence in your sleep, and then you can come up with statements such as the one that we just read out there. And insomnia is a situation where you worry that your sleep controls you. But when you go through CBTI, gradually you control your sleep. In other words, you regain confidence in your ability that when you walk into your bedroom and you tuck yourself in at night, there is a consistent solid seven-plus hours of sleep awaiting you, and it is there for most people. So I would just sort of put a sticky on that and say please don't despair. I understand if you're struggling with sleep why my words of saying seven to nine hours of sleep is just fine would feel like an impossibility or even an assault on your belief in your ability to generate sleep. But honestly, for most people, that capability is very much present inside of you.

Dr. Rangan Chatterjee 15:21 Yeah. I mean, thanks for that. That's, that's very, very helpful. I'm just wondering, one could interpret that question another way, and obviously we don't know how the person meant it, but it could also be that I don't feel I have enough time in my life-

Matthew Walker 15:36 Yeah

Dr. Rangan Chatterjee 15:36 ... for seven to nine hours sleep. I'm too busy.

Matthew Walker 15:41 Yeah.

Dr. Rangan Chatterjee 15:41 If that was the way they meant it, how would you frame it for them?

Matthew Walker 15:46 I think there's a number of ways that you can do it. Um, the first is practical, the second is, um, contextual and belief mental. Um, belief mental contextual, what I mean by this is saying many of us think of sleep like a cost. And so you're working away at night and you think, "Well, you know, I don't wanna waste my time going to bed right now. That's gonna come at a cost of me 'cause I could do an extra hour of work." I think of sleep in exactly the opposite based on the weight of the evidence. If I get to bed tonight at the right time, it is an investment in my productivity tomorrow. It's not a cost to my productivity today. Because what we know is that when you are underslept, your efficiency in terms of getting done what you need to get done is utterly miserable. Less sleep does not equal more productivity. That was not true in the rote industrial era, and it's never been more true now in the digital knowledge era. And so that evidence we can dispel in terms of a myth. You know, I think of it, it a little bit like, you know, boiling water on a stove. You know, why would you boil that sort of pot of water, um, on medium heat when you could do it in half the time on high? And that's exactly what happens when you're getting sufficient sleep. The next part of that question, though, may not be about your belief system. Maybe you do believe that sleep is an investment and it's great and it helps with productivity, but your day is just such that you can't manage that amount. I would then really start to take a step back and say, "But honestly, is that true?" And think about what you want in life. What do you really want? And with concrete details. Do you want to live a life that is going to be filled with health and is not inviting disease and sickness into your body or your brain? And if those are goals that you have, which I think for most people are, then coming to terms with the reality that we just have to find the right amount of time. You know, I think increasingly people are finding the right amount of time to exercise, and they're also finding the ability to purchase food that is of better quality and make food, um, that is of higher quality. And I think we need to take the same mentality approach to sleep. The final thing I would say is practically, okay, how can you help me even just get a little bit more sleep in terms of opportunity time? I think there are several tricks, and I'll just give you, uh, two of them. Often we have a wake-up alarm. We set an alarm to wake up in the morning. Very few of us have a to-bed alarm [laughs] . Why, why not? And so set your alarm, um, that would give you an eight-hour sleep opportunity. Now, you're probably gonna ignore it, you're probably gonna... And give your ability to have a snooze button on that too so you can say, "Okay, I'm gonna watch five more minutes of Netflix," and you snooze again. But that persistent nagging of the notification will probably get you into bed a little bit earlier. The second thing is this. In the w- at least an hour before you are planning to go to bed, get changed into whatever you're going to wear for bed, get changed into your sort of your pajamas, your bed clothes, and then brush your teeth, you know, take your makeup off, floss your teeth, do everything, wash your face, do everything that you would normally do just before you go to bed, but an hour before, so that when that to-bed alarm goes off, you don't have this 15 or 20 minutes of, okay, I need to sort of now go into the bathroom, do all of these things. And instantly you will add 15 minutes of time to your sleep opportunity. That's like compounding interest on a loan. 15 minutes every night, every week, every month is non-trivial. So that's a very long-winded answer, but I think changing your mindset, and then with some h- tricks and habits, I don't like the word hacks, but hopefully that can try to help with a difficult schedule.

Dr. Rangan Chatterjee 20:13 Yeah. I mean, that's absolutely brilliant. Um, and, and I think what's really encouraging in terms of what you said there, Matt, is that you don't have to be black or white about this. You know, wherever you currently are, assuming you're currently underslept, you're saying that even 15 minutes extra a day is gonna have a difference on your health and wellbeing, and I think that's very powerful.

Matthew Walker 20:41 It really, it really can. You know, if we look at the evidence, there was, uh, some fascinating data recently on, um, the importance of REM sleep for lifespan. Um, and what they found was that for, I think it was something like for every 5 or 10 minutes, or maybe it was 15 minutes of, um, a reduction or a loss of REM sleep, there was a 13% relative increased risk of, of premature death. And so, you know, we don't have to... I, I like a guy called, um, who I think you've had on your show maybe, BJ Fogg, who's at Stanford.

Dr. Rangan Chatterjee 21:19 Yeah, I know BJ well. Good friend of mine. He's brill.

Matthew Walker 21:21 Oh, he's, he's lovely. Does some great work. And he sort of, you know, thinks very much about sort of practical behavioral change for human beings. And a great example of this is getting people to start flossing their teeth. And you say, "Tonight, you have to floss your teeth," and it feels like a Herculean task if you're not really someone who does that. And sort of his ethos would be, "Okay, tonight all I want you to do is floss your front two teeth, and you cannot floss any more. Just your front two teeth. That's it. And do that for a week, and you are not allowed to do any more than that." And then gradually floss, um, two more teeth in addition, and it just becomes more of a manageable task, and I think it's the same way with sleep. You know, don't say, "Oh, I, I need to add now an hour and f- you know, 20 minutes to sleep because I heard Matt Walker going on about something." Just try 15 minutes. You know, and even if you can get to bed 15 minutes earlier, then set your wake-up alarm five minutes later, and that way you've already gained 20 minutes. And in truth, y- your life won't feel that much different, but yet you've given sleep 20 extra minutes back in terms of its longevity and healthspan boost.

Dr. Rangan Chatterjee 22:44 Yeah, and you think about that not just in terms of 20 minutes in one day. It... That's 140 minutes in a week. That's, uh, thousands of minutes in a year. You know, it's like compound interest in the bank, isn't it? It's, it's just-

Matthew Walker 22:58 That's right

Dr. Rangan Chatterjee 22:59 ... gonna keep plugging away and growing and growing and growing. So yeah, really, really inspiring answers there. Um, the point about unbroken sleep and polyphasic sleep-

Matthew Walker 23:11 Yeah. So one of, I think, the, the really powerful, um, emerging sets of data that we've had in sleep science over the past five years is the understanding that it's not just about the quantity of your sleep, which is what we've been talking about, it's also the quality of your sleep. And when I say quality, I mean both at a macro level in terms of how consolidated or consistent your sleep is versus how fragmented or broken your sleep is. That's one way that we describe sleep quality. Another way that we describe sleep quality is the electrical quality of your sleep, meaning the depth of the electrical brainwaves that you're having, the deeper that electrical brainwave activity, the better the quality of that deep sleep. And what we've discovered is that a reduction in the quality of your sleep, um, on both of those counts can be as, if not more detrimental than a reduction in the quantity of your sleep Now, to be clear, both of them are necessary. You can't just sleep for five hours and have great quality sleep and expect that to be okay, but nor can you have eight hours of sleep that is very poor quality and expect to be okay. And what we're describing here is if you are, let's say if you're someone who, you know, wakes up for 15 minutes and then you fall back asleep and then, you know, another moment it's 10 minutes and you fall back asleep, and maybe you have, you know, two or three of those types of awakenings during the night, don't worry. That's, that's normal. That's perfectly okay. Um, some people won't have that, but some people will. Um, and that's, that's okay. That builds into what we spoke about at the top of the conversation, which is sleep efficiency, that, you know, we'll spend a fair amount of, uh, the night about, you know, 10, 5, 15% awake, and that's part of it. But having a long stretch of time awake, such as an hour, is not really healthy. It's not really beneficial, and it's also not really natural. Part of the reason people think it is natural is because of a practice that emerged, it seemed to emerge during the sort of Dickensian era, which was something called first sleep and second sleep. And if you look at this historical writing, it's very clear that this was happening. People would sleep for three or four hours, then they would wake up, and then they would make food, they would play music, they would write, they would make love, they would socialize, and then they would go back and have another three or four hours. So it was two sleeps. But there's nothing really, with the exception of one study that people typically cite, there is nothing in our biology, our biological rhythms, that suggests that that's how we should be sleeping at night. But I'll come back to two type, two phases of sleep in just a second. So staying awake for an hour or so at night and certainly lying in bed for longer than 25 minutes is a bad, a bad idea, and here's why. If you are lying in bed awake, your brain starts to learn the association that this thing called the bed and this place called the bedroom is the place where I'm awake. And your brain is such a remarkably associative device that it bonds those two things very strongly. And this is why people will often say to me, "Look, you know, Matt, I'm falling asleep on the settee when I'm watching telly, and then I get into bed and I'm wide awake and I don't know why." And the answer is because you've learned the association now that your bedroom is the place of being awake and not asleep. So the advice is the following. If you've been awake for, let's say, you know, longer than 25 minutes, if you've been trying to fall asleep and it's been 25 minutes, or you're trying to get back to sleep and it's been 25 minutes, get up and get out of bed. Go to a different room, and in dim light, just do some, whatever works for you, do some sort of gentle stretching, meditation is fantastic, which we can speak about, or reading under dim light. Don't check your phones, don't eat, because they will become triggers for you to start waking up. And then only return to bed when you're sleepy. And there is no time limit for that. And gradually, if you do that, your brain will relearn the association that your bed is the place of always consistent, solid, sound sleep. And so the analogy I often give here is that, you know, we never sit at the dinner table waiting to get hungry. So why would you lie in bed waiting to get sleepy? And the answer is, you shouldn't. You should get out of bed. And so that's the best advice for prolonged, uh, time awake, and hopefully gives you some back context as to sleep quality versus sleep quantity.

Dr. Rangan Chatterjee 28:22 Yeah. Thanks, Matt. Really, really helpful. Um, okay, so I'm gonna go back to my sheet of questions. Obviously, the world has changed in 2020-

Matthew Walker 28:34 Mm-hmm

Dr. Rangan Chatterjee 28:34 ...um, because of the COVID-19 pandemic. The way many of us live and interact and work has dramatically changed. So have you seen a difference in sleep quality, sleep duration? Basically, have you seen changes in the way people are sleeping? And then the follow-up to that is, what have we learned this year, if anything new, about sleep and its effects on the immune system?

Matthew Walker 29:05 Yeah, two great questions. So regarding sleep and COVID, we have certainly seen quite dramatic changes in sleep. Um, and there's now s- several scientific papers that have already been published on this. And the way it, um, sleep has changed is probably in three different ways, the amount of sleep that we're getting, the timing of our sleep, and then finally, how we're dreaming, [chuckles] which is a fascinating component. Let me start with amount. Um, there was an early report, um, from a sleep tracking, um, uh, company, uh, I think it was almost, uh, over 60,000 Americans, and what they found was that nationwide, there was about a 20% increase in the total amount of sleep. Um, two more recent papers, peer-reviewed papers, uh, one from a European group, one from a US group, um, both of them suggested that overall total amount of sleep had increased. Um, in one of them, it increased by 15 minutes, the other by 30 minutes during the weekday. Um, and then it had increased by 24 minutes during the weekends. In other words, you know, relative to what most people were sleeping, uh, at the weekends, there was less of an increase, but it was during the weekdays when people got the greater bang for the buck. Also what we found that was interesting though is that some people were-- there was a, a considerable portion of people for whom their sleep quality had become much worse. And in fact, there's now emerging this sort of, uh, Covid-somnia, um, as it's being called, which is a form of insomnia that we see now, um, because of the, the, the COVID pandemic. Also, a recent report demonstrated that the search term for insomnia on Google Trends has escalated many-fold since COVID hit. So we know that this is not quite as rep-- it's not as clean cut as I'm making it sound. It's not just that overall people are sleeping more and people, um, people sort of, you know, having, um, longer durations of sleep. I think what we're going to find is a much more nuanced story. There will be at least two clouds of data. One of them will be a group that is indeed sleeping more, and we'll come on to the reasons as to why. But I think there will also be a cluster, a cloud for whom sleep has become demonstrably worse, both in duration and in quality. Why? Well, some people have lost their jobs. Other people don't know if they will keep their job. Other people just have high anxiety overall because of the state of the world, understandably so. So I don't think it's as clear-cut as, as those data would suggest. The second interesting part though, which I think is if there is an upside, a sleep upside of COVID, it's the following. It's not just the amount that we're sleeping, it's the timing of our sleep. And what we've discovered is that most people are now going to bed on average about thirty minutes later than they would otherwise, and they're waking up a little bit later. In fact, they're waking up considerably later, and that's how they're getting on average that increase in sleep duration. What this means to me is that finally, because people don't have to get up in the morning as early, they don't have to build in that commute time, they don't have to wake up even earlier to get the kids to school in the morning, you are able to sleep in closer harmony with what we call your chronotype. Are you a morning type or are you an evening type? Now, for the morn-- society is designed for and desperately biased towards morning types. And if anything, we chastise the evening types as being these kind of people who are a bit lazy, they can't get it together, they can't be in work at the office at eight clock in the morning, and plus, I didn't see them at the gym at six o'clock in the morning. So what's wrong with them? And it's not their fault, and we can come on to chronotype because it's largely genetically determined. It's not your fault if you're an evening type. And so I think what's happened with COVID remarkably is that it's revenge of the night owls [laughs] that finally we're getting the chance to sleep in a way that's closer to the natural rhythms of our biological twenty-four-hour clocks and less so driven by the dictate and the mandate of society. So I think that's another way the timing of our sleep has changed. The last part of this is dreaming. We've been hearing or we started to hear very early on that people was reporting dreaming more and also having COVID dreams. Why is this? Why would that be? I think it's for two reasons. The first is just what we described. People are sleeping later into the morning. Now, previously on our last, um, episode, we spoke about sleep and its structure, that we have these two types of sleep, non-rapid eye movement sleep or non-REM sleep, and rapid eye movement sleep or REM sleep. And REM sleep is the principal stage within which we dream. But you don't get equal proportions of those two types of sleep with each ninety-minute sleep cycle across the night. What happens is that in the first half of the night, that's when you get most of your deep non-REM sleep. But in the second half of the night, and particularly in the last couple of hours of the morning, that's when you get most of your REM sleep. So if REM sleep is the state during which we dream, and now as a society, we are sleeping later into the morning, then probabilistically, we are giving our brain the chance just to simply have more of this thing called dream sleep, so no wonder people are reporting dreaming more. That's the first issue. The second issue comes onto the specificity, which is, yes, people are dreaming, but why are they dreaming about COVID? What we've learned about REM sleep dreaming among many of its other benefits, not just in terms of increasing your lifespan and also promoting creativity, REM sleep is a form of emotional first aid. REM sleep provides this type of, um, mental health therapy. It's, it's overnight therapy. And what we've discovered is that it's during REM sleep and dreaming that we take these difficult, sometimes traumatic experiences from the day, and REM sleep acts like a nocturnal soothing balm, and it just takes the sharp edges off those emotionally difficult concerns, so that when we come back the next day, we've processed those emotions, and we feel better about those concerns. So in other words, it's not time that heals all wounds, it's time during sleep and specifically dream sleep that provides that form of emotional convalescence. And I think when you have, and we've done this in the laboratory, we've seen this in our experimental work, when you challenge people with difficult emotional experiences during the day, they actually have a rebound that following night where they increase their amount of REM sleep, their dream sleep, as if the brain and the sleeping brain is responding to the demands of your emotional life because you need more overnight therapy. And so that, I think, is another reason why people are dreaming more. It's not just because they're sleeping later into the morning. They also need their dream sleep more to process the difficult, emotionally challenging way of life that is the COVID era. Does that sort of help explain it?

Dr. Rangan Chatterjee 37:25 Yeah, Matt, that, that was brilliant actually. So, so many thoughts coming up as, as you describe that. It's really quite incredible to think about the REM sleep as emotional first aid. I think it's, um, I think it's just a wonderful way to think about it. And, you know, I'm struck by this idea that we touched on last time, Matt, but the, this whole idea that society is really set up in such a way that so many of us cannot access our basic human rights, which is a great night's sleep.

Matthew Walker 38:00 Mm-hmm.

Dr. Rangan Chatterjee 38:00 You know,

Dr. Rangan Chatterjee 38:01 whether it's shift work, whether it's just the general pressures, school start times, it's, you know, if anything-

Matthew Walker 38:06 Yeah

Dr. Rangan Chatterjee 38:07 ... good is to come out of, uh, what we went through in 2020, um, you know, maybe it's a reprioritizing of sleep and going, "Hey, look, why don't we start changing things, school start times, office start times-

Matthew Walker 38:22 Hmm

Dr. Rangan Chatterjee 38:22 ... the way society is structured," because that's what people are up against a lot of the time.

Matthew Walker 38:28 I think you're so right that what this has taught us is that we don't need to be, you know, anchored or, um, enslaved in some ways in this penitentiary of, you know, the Type A personality, um, work mentality or work schedule. You know, there are so many adaptive ways that we've now developed that allow us to be... You know, I'm not saying we're as productive anymore, and I know there's a lot of challenges for businesses, um, for many different reasons. But when we return to a way of life, I do think that some things will remain subtly different, and I suspect it will be subtle, unfortunately. But I do hope that, for example, employers realize that, you know what? It's fine for you to, you know, not have to be here until 10 o'clock in the morning, and that way, you know, you can work through until, you know, 6:00 or 7:00. But we've realized that, you know, for that first meeting in the morning, maybe you could take it at, you know, 8:30 and do it virtually from 8:30 until 9:15, after you've finally woken up at 7:45 rather than 6:45. And then you can sort of make your way into work, um, at a way and a pace that's more relaxed, and that way you can actually regain what is naturalistically your sleep tendency. I like that idea. I think, though, the problem is sleep still has this misperception, whereas it's not the same for diet or exercise. So employers are very, I think, enamored with this idea of saying, "Yeah, let... This great. Let's give you, you know, a discount on a gym membership because it keeps you healthy, and it keeps you in work, and, you know, lowers what we call, um, sort of pre-absenteeism at work, as well as absenteeism." Um, so I think-- A- and they see that as something virtuous, um, that they, you know, that people are working out. And then with diet, you know, I think, you know, in the cafeteria, developing healthier, you know, selections of food seems to be a good thing. It's a virtue signal from a company. Even if they don't really believe in the health benefits to keep their employees healthier and, you know, more productive, even just at the superficial level, they're ready to embrace it. The problem is people have the opposite mentality with sleep, which is that getting sufficient sleep is associated with being slothful or being lazy. And it's nobody's fault. I don't mean to be finger-wagging here because most, for, you know, much of the past 20 or 30 years, despite the science changing, people still believe that when we sleep, our bodies simply are resting, and our brain is dormant, and there couldn't be anything further from the truth. All of your major physiological systems in your body undergo a dramatic overhaul during sleep. And every operation of the mind, all of the networks of the brain are being augmented. Memories are being saved. Memories are being shifted from short term to long term. Your emotional networks of your brain are being recalibrated and retuned. Your-- Some parts of your brain are getting reconnected that have been degraded across the day, particularly with your prefrontal cortex, so you're better able to make decisions and be more rational as an individual. And so as a consequence, you know, in fact, some parts of your brain are up to 30% more active than when you're awake, when you're in certain stages of sleep. But we still have this belief that sleep, because it's a, quote-unquote, "dormant state," well, then it's a waste of time. And so why should we actually give people the opportunity to sleep if it's something that we don't see as virtuous? In fact, if anything, we see it as quite the opposite. And why do we see it as the opposite? Because we don't really understand how beneficial and how active and essential sleep is as a process. I mean, it's the reason that Mother Nature took 3.6 million years to put this necessity of a seven to nine-hour sleep, um, period in place, and for us to come along and think that we can get away with less than that is, is, is probably hubris.

Dr. Rangan Chatterjee 43:09 Yeah. I think one of the, the many reasons that your first book, Why We Sleep, has proved so popular in so many countries is 'cause it's really, I think it's really hit the zeitgeist. It's really doing such a wonderful PR job on the importance of sleep and why every single one of us should probably prioritize it more than we're currently doing. Um,

Dr. Rangan Chatterjee 43:35 I've got to say at the, the stage of life I'm in, Matt, it is... I've been moving this way for the last few years, but, you know, my sleep opportunity is close to non-negotiable. And for me, y- I, I like to be in bed, uh, you know, we're in the British winter at the moment as we have this conversation, Matt, you, I'm sure you can remember what the British winter-

Matthew Walker 43:57 Oh, I remember it all too well [laughs]

Dr. Rangan Chatterjee 43:59 ... w- w- was like. Um, I'm in bed often by half 8:00, quarter to 9:00. I like to be asleep-

Matthew Walker 44:04 Mm-hmm

Dr. Rangan Chatterjee 44:04 ... by 9:30 PM, and I-

Matthew Walker 44:06 So you're an, you're quite an extreme morning type then?

Dr. Rangan Chatterjee 44:09 I am. I, I've always been. I love mornings. Um, I-

Matthew Walker 44:13 Right

Dr. Rangan Chatterjee 44:14 ... I will typically be up 5:00, half 5:00, and I have a little morning routine, and I-

Matthew Walker 44:18 Right

Dr. Rangan Chatterjee 44:18 ... you know, I love being awake and doing a few things before my wife or my kids get up. It's, it's just how... I probably adapted to being a morning type, I guess. Um, but what's really interesting is that I've been thinking about emotions a lot recently and, you know, really, and you touched a bit on this when you mentioned that as we're sleeping longer in the mornings, we're getting more REM sleep, which is when we, I think, process a lot of our emotions. And there's a form of therapy I've done on myself over the past few years, uh, called IFS, internal family systems, and-

Matthew Walker 44:56 Mm

Dr. Rangan Chatterjee 44:56 ... uh, it's really helped me. I feel a lot lighter in my life in general having gone through this over a number of years. And what's interesting is you go into, uh, experiences, uh, that you may have had in your life, and there's a system of doing it, but you sort of, you reframe them. Um, so you reinterpret them a different way basically than you may have interpreted it, let's say, when you were a child. And I think that from what I understand is that you reinterpret it, and then when you're sleeping, things get laid down differently. So I guess my broader-

Matthew Walker 45:31 Mm-hmm

Dr. Rangan Chatterjee 45:31 ... question is how much do we know about our emotions and our memories and how they all get rewired and processed when we sleep?

Matthew Walker 45:42 We know a lot now, or at least... W- well, I shouldn't say that. Um, w- we never know enough as a scientist, um, and I'm always ignorant, um, and I remain, uh, ignorant, and that's, I think, the best way to be as a scientist. But we do have some more information. But let me just come back very quickly to what you said. What you're describing is something in the memory, um, science literature that's called consolidation and reconsolidation. So we used to think, um, that the way the memory worked is a little bit like a Word document. So you open it up, and you type in all of that information, which is you having the experience and acquiring that. Let's say you're in a lecture, and you're listening to a lecture, and then you hit the Save button on that Word document, which is what we call the consolidation process. And then at some point, you can come back, and you can double-click that file, and you can bring that memory back to mind. You access that memory. You recall the memory. But we used to think that that memory at that point was then fixed, that there was nothing that you could do about it. It would be as though you double-click that Word file, and now it just is kind of grayed out, and if you try to type in anything, it's, you can't change it. It's just fixed. That's the memory for, for life. It's not true now. What we've learned is that every time you recall a memory, just like a Word document, you open it back up to the possibility of change, both you can change its content, you can update it, you can modify it, maybe you can even remove some parts of it. But also, you can update the context and specifically the emotional tenor of that memory, and that's exactly what you're describing. And then you hit the Save button. So the memory originally, you, you created it, and you saved it, which is called consolidation, but then you double-clicked it. You recalled it. You modified it, and then you reconsolidated it. And so what this is, why this is important is for the reason that you described, that if you have a memory that is, you know, difficult or painful or challenging from your, you know, your prior past, it doesn't need to remain that way, and this is what sort of reconsolidation therapy, um, often, um, focuses on. Let's bring that difficult experience back to mind, and let's see if we can restructure it. Can we recontextualize it? Can we frame it in a different way that's neutral? It doesn't have to be positive, but can we reframe it in a way that's neutral, or can we reassociate it with something that isn't traumatic, and therefore can we dissipate that? So I just want to sort of give you af- sort of cognitive neuroscience brain, and you will know this of course already, but brain science affirmation of that therapeutic technique. What happens during sleep, however, is, is really interesting. We came up with, um- A theory a while back that was looking at emotional experiences, emotional memories, and at the time, we knew that sleep helped strengthen memories. But what we proposed is that when it comes to emotional memories, you sleep to forget and you sleep to remember. You sleep to forget the emotional charge related to that memory, but yet you sleep to remember the details of that experience. Because let's say that you have a difficult experience such as a trauma event. Let's say you're a combat veteran or you're somebody, um, let's say who's been assaulted. Um, what you don't want to do is throw out that memory. That's not adaptive. You know, let's say that you were walking home at night, and you chose the shortcut to walk down that alley, and then that's where the assault happened. You don't want to forget the important details of that experience because you don't want to walk back down that same alley again. That experience was meaningful, and you should remember it. But the pathological part of that, when it becomes something like PTSD, is that the emotion stays with the memory. In other words, every time the, you know, the, the soldier is in the car park at Sainsbury's, and they hear a car backfire, that immediately triggers that trauma event of the battlefield. What they are doing there is having a flashback memory. They are not only reliving the memory, the information of the experience, they are also regurgitating the same visceral emotion that they had at the time of the experience. Why is this relevant to sleep? Well, what we've discovered is that it's during sleep when the brain essentially depotentiates the emotion. In other words, REM sleep dreaming takes this sort of emotional memory, and think about it like an orange, that you've got the fleshy good stuff in the middle, you know, that's the information, and then you've got this bitter emotional rind around the informational orange. Well, what sleep will do is divorce the emotion from the memory so that when you wake up the next day, yes, you can still remember that information, but what you don't do is regurgitate the same visceral reaction that you had at the time of the experience. In other words, sleep has stripped away the emotion from the memory, and that's one of the most powerful reasons why we've come up with this idea of REM sleep dreaming being overnight therapy. You sleep to remember the experience, but you sleep to help forget some of that emotion. That's why to me, sleep is one of the best forms of therapy, and it's the reason I think there's a wonderful quote by an entrepreneur called E. Joseph Cossman. He once said that, "The best bridge between despair and hope is a good night of sleep."

Dr. Rangan Chatterjee 51:58 Yeah, that says it all. [laughs] It's, it, it's, it's really incredible, Matt, to hear, hear this because we can talk about sleep for our risk of type 2 diabetes and our risk of cancer, but this is using sleep as a tool. This is using sleep as a way of processing your life, enhancing your life. You know, um, who wouldn't want all those benefits you just mentioned about our emotions? We know anxiety, depression, all kinds of things are going up year on year, and there's just so much in that that, that if we can get in the habit of really prioritizing sleep... I, you know, I don't know about you, Matt, but certainly in, in clinical practice for me, for many people, the first job is just to give it the priority.

Matthew Walker 52:48 Yeah.

Dr. Rangan Chatterjee 52:49 Like, it's, it's just something that gets squeezed in and fits in around everything else. And once you understand it, and you can give it priority, for many people, that's all they need to do. Of course, some people need a bit more help than that. But, um, when, when it comes to REM sleep, and you mentioned your own tracker that you use, and I, I, I want to come onto trackers because a lot of people have questions about that. Um, I think I have noticed that when I don't have a good night's sleep, my REM sleep goes, and I think I've-

Matthew Walker 53:16 Mm

Dr. Rangan Chatterjee 53:16 ... noticed that when my caffeine intake creeps up, that my REM sleep gets affected the most, and I'm, I don't know if there's any science behind that.

Dr. Rangan Chatterjee 53:26 Do we know what things block REM sleep, and do we know what things enhance REM sleep?

Matthew Walker 53:32 We do. Um, and so caffeine typically, depending on sort of when you're taking it, um, has been most demonstrated to have an impact actually on the quality of your deep non-REM sleep. But there are some studies that show that it will fragment your sleep, so you're waking up throughout the night more times. And therefore, when it comes to sort of that consolidated sleep cycle, you may not be getting enough REM sleep. So both can take a hit. Another way that you can do a real number on your REM sleep, if you want to find a way to chemically, potently block your dream sleep, um, just have a couple of drinks in the evening. And, um, drinking is, is one of the ways that, once again, you will fragment your sleep. You will wake up many more times. Your sleep is much more, um, fragile, um, when you have alcohol in the system. It's much more likely that you're going to wake up, and when you do, it will be harder to fall back asleep. But what we found is that some of the metabolic byproducts of alcohol, the aldehydes and the ketones, the aldehydes, sorry, and the ketones, um- Particularly the aldehydes it seems, those things will, um, potently suppress REM sleep. And in fact, that's why, um, we see in some alcoholics, um, they have a near absence of REM sleep, and when they actually become, uh, they go through sobriety, there is this massive rebound of REM sleep when they start sleeping sober. The reason is because their brain has been so starved of REM sleep because the alcohol has been suppressing it. So those are two very powerful ways that you can manipulate, uh, your sleep for the worse. Um, and alcohol, you know, is one of the most misunderstood sleep aids. It's really not a sleep aid at all, but many of us turn to it. We think of the nightcap. Um, but that evidence is very strong. Now, you know, uh, and I want to come on to actually caffeine 'cause it's something I've changed my mind on, um, since we last spoke and, um, but I don't want to sound puritanical. I think, you know, when the book came out, um, you know, some people I think felt as though the message there, and then I, I, I sort of did a, a TED Talk, and I think people felt as though perhaps some of that was, you know, a little bit, you know, sleep or else, sort of, you know, dot, dot, dot. And I, I understand that, and what I want to say is the following: I don't mean to sound puritanical about alcohol and caffeine. You know what? Life is to be lived to a degree, and I as a scientist have no business telling you how you should live your life. All I want to do is share with you the science and the knowledge of sleep so that then you are empowered with the ability to make whatever choices that you want, uh, in life, uh, for yourself. You know, having, you know, a, a glass of wine, you know, um, you know, a night a week or two nights a week, sure. You know, I can't tell you as a scientist that that won't have an impact on your sleep. It will, and I, I can't lie to you about that. But, you know, there is also something to be said for, you know, having something that you like as well. Of course, the politically incorrect advice that I would never share with you is that you should go to the pub in the morning, and that way the alcohol is out your system by the evening and there's no problem at all. But I would never say that, uh, on a public podcast. But, um, uh, hopefully that sort of gives you a sense of the impact of caffeine and alcohol. But you're right. I think the shift of, of us understanding sleep is not just about physical health, it's also about mental health. And you spoke, by the way, just, you mentioned anxiety, and I know it's something that, you know, um, in your, um, books, um, you've really drawn a sharp focus on mental health, which we don't hear a lot about from doctors. We hear a lot about physical health, but I think it's less so common that doctors help us understand our mental health, and anxiety is a big problem. It is at astronomical rates in First World nations right now, and sleep is a key part of this ingredient, too. And I'll-- We published a study just, um, a year or so ago, which in some ways frightened me. What we found is that when you causally deprive someone of sleep, you instantly trigger a dramatic escalation of anxiety, and it is dramatic. In fact, all of the participants in our study began, um, healthy. They had no signs of an anxiety disorder. By the end of one night of no sleep, 50% of them had escalated to a level of anxiety that would be clinical grade, requiring treatment, which t- it just blew me away. And what we also were doing, we were assessing their anxiety across the night, and what we found is that there was a dose-dependent relationship. The longer you go without sleep, the more anxious you become. And we discovered what the brain mechanism was regarding that, um, which I, I won't go into here for time's sake. But what we also then discovered was that even subtle changes, we did a much bigger study where we tracked people in real world conditions, free living conditions, and we tracked their sleep and we tracked their anxiety, and what we found was that even modest night-to-night reductions in your sleep quality were associated with consequential day-to-day increases in your anxiety. So your sleep from one night to the next was dictating your anxiety from one day to the next. And finally, what we found is that sleep and the electrical quality of that sleep when you get it actually provides essentially an anxiolytic. [laughs] It deescalates anxiety, just as you would, uh, imagine. So I just wanted to come back around to that mention of anxiety there, too, because we've really recently discovered how causally, not associational-wise, causally related sleep is to anxiety.

Dr. Rangan Chatterjee 59:50 Yeah. Thanks, Matt. And I really appreciate what you said before about sharing information so people can make up their own minds, and, and that's... You say as a scientist it's not your job to tell someone what to do. I also feel that as a doctor, if I'm honest, that-

Matthew Walker 1:00:06 Hmm

Dr. Rangan Chatterjee 1:00:06 ... as a human being, I don't have a right to tell somebody else what to do, but if they ask for my opinion, I want to share information with them on what I think might be helpful. And-

Matthew Walker 1:00:15 Mm-hmm

Dr. Rangan Chatterjee 1:00:15 ... it's like, you know, alcohol affects your sleep, right? If people are empowered to know that, then they can make a choice. But a lot of people are under the impression that alcohol is a sleep aid, and you covered this beautifully on our first conversation together, that it's a sedative, it's not a sleep aid, and it's-

Matthew Walker 1:00:32 That's right

Dr. Rangan Chatterjee 1:00:32 ... and then-

Matthew Walker 1:00:33 Sedation is not sleep, but we mistake that-

Dr. Rangan Chatterjee 1:00:35 Yeah, and so with that in-

Matthew Walker 1:00:36 ... when we have alcohol

Dr. Rangan Chatterjee 1:00:36 ... with that information, that individual now can make their decisions. If they decide to have a few glasses of wine before bed and their sleep is impacted, but they get more enjoyment out of that wine than they do out of a good night's sleep, well, that's kind of up to the individual really to make that decision. So I wanna thank you for making that point.

Dr. Rangan Chatterjee 1:01:00 You also mentioned you changed your mind on caffeine. What did you mean when you said that?

Matthew Walker 1:01:07 So I think in our last conversation, um, you know, it, it's very clear that caffeine is no friend of sleep, um, and it impacts your sleep in, in three different ways. Um, the first is that it can make it harder for you to fall asleep, and we all know that caffeine is a stimulant. Um, and it's one of the few psychoactive stimulants that, uh, s- you know, some people will, um, allow children to have, which is, is an interesting conversation. The second issue is that, um, caffeine, um, will also make your sleep more fragile, so you're more susceptible to waking up throughout the night. And then the third component of caffeine, as we spoke about before, is that even if you can have an espresso with dinner, and you tell me, "Look, I can fall asleep and I stay asleep, so this-- I have no problem," the issue there is, comes back to electrical quality that we spoke about. When we measure the electrical brainwave quality of your deep sleep with and without caffeine, it's not the same. And so you may not wake up, but you're actually going to be experiencing more shallow sleep rather than deep quality of sleep. And then the next morning you wake up, and you don't feel as refreshed, you don't feel as restored by your sleep the next morning. But you don't remember waking up, and you don't remember having a hard time falling asleep, so you discount the idea that it could be the caffeine. But now, because you're unrefreshed, you're reaching for three or four cups of coffee in the morning rather than one, and so goes this dependency cycle. How I've changed my mind on caffeine, though, is to become much more relaxed, because as with so many things, as you know as a doctor with pharmacology, it's not just the dose, but the timing that makes the poison. And if you look at the evidence, there are remarkable health benefits of, um, caffeine, and this evidence is so powerful. In fact, there was a recent meta-analysis, and meta-analysis is just simply a fancy scientific term meaning you gather together all of the single studies, and you kind of collate them all to get one big picture average. And it's a very powerful method in science. And there was overwhelming evidence that caffeine was very good for de-risking numerous health conditions that none of us wish for. However, if you dig a little deeper, the story is not quite s- So firstly, I'm, I'm much more bullish on the idea of people having caffeine, but at the right dose and the right time. So having caffeine before, let's say, you know, ten o'clock in the morning and in, um, mild to moderate doses, I think is just fine. If anything, I would tell you, you f- if you like doing that, you should absolutely do that based on the health benefits. Um, but once you get past sort of, um, three cups of coffee, then the health benefits start to take a turn back on themselves. They start to go in the opposite direction. So again, that's the dose. But when it comes to sleep, it's also about the timing, because we know that caffeine has a half-life of about, uh, five to six hours. It has a quarter life of ten to twelve hours. In other words, if you have a cup of coffee at noon, a quarter of that caffeine is still in your brain at midnight, and you're not going to be able to sleep as well as you could do otherwise. Um, so trying to cut yourself off from caffeine, uh, at the right time, but still enjoying it and thrilling in it is just fine. Some people are much more sensitive to caffeine than others, though. There's a good variability, and we know the genetics and the enzyme behind that. So you may not benefit from caffeine even if you stop at, you know, even one cup of coffee in the morning, some people tell me can-- they notice it in their sleep in the evening. What I would note is a subtlety, however. If you look at the data now, it's actually not the caffeine, because when they did the same types of analyses for decaffeinated coffee, they got very similar health benefits. Different types of conditions were benefiting, but for the most part, you've got some wonderful benefits from decaffeinated coffee. So what on earth is going on here? Well, there's a writer, a wonderful writer and a good friend of mine here in Berkeley, California, called Michael Pollan, who's written some wonderful books, and he wrote a book recently called Caffeine, and he interviewed me for it, and we discussed the science, and we, we really researched the science. What it turns out is that for what people call the sort of the standard Western diet, which is actually a very poor diet, but it's what many people in First World nations eat, they have a poor micro and macro nutrient profile. We're just not eating well. But it turns out that the coffee bean is very rich in antioxidants, and most people, because their diet is so poor, the only thing that gives them an antioxidant dose is their cups of coffee in the morning. So the health benefits that you get from a cup of coffee are not really due to the caffeine, it's due to the antioxidants that take a joy ride on this vehicle called a cup of coffee in the morning, and that's why you see the health benefits, and that's why you also see the health benefits from decaffeinated coffee. But I've changed my mind. I was probably just too rigid and puritanical. I was just so passionate about sleep, and before the book came out, you know, there really wasn't a health conversation that had been going on at the level that I wanted it to be, at least not that I'd been helping it to happen. And I think, you know, it's like a Richter shock. You sort of firstly you go to sort of extremes, and then you find your sweet spot, and I think I'm coming to a better sweet spot right now. I'm still not perfect, but one of those places I've come to a sweeter spot on, I think, is caffeine.

Dr. Rangan Chatterjee 1:06:56 That's fascinating. I guess what you're saying about Michael's work and the work you, you, you sort of discussed is potentially if we've already got a Nutrient-rich diet, right? Which of course, many of us don't. I wonder if we already have a nutrient-rich diet, do we get the additional health benefits then from coffee and caffeine or a-

Matthew Walker 1:07:23 Right

Dr. Rangan Chatterjee 1:07:23 ... do you know what I mean?

Matthew Walker 1:07:23 Exactly.

Dr. Rangan Chatterjee 1:07:23 It's like, that's the, it begs that question for me

Matthew Walker 1:07:25 Well, that's, you know, that, you, you, you know, I, I love what you're saying. This is a beautiful science mind that's on display here. You're absolutely right. Let's now start to, if that's, that's the associational evidence, that's what sort of works w- we, we think is happening. Now let's do some more controlled prospective studies. Let's hold constant an optimal, you know, micro and macro nutrient, um, intake, and then let's add coffee back to the equation. Do you still get benefits above and beyond that? Because you're right, it's a little bit like oxygen saturation. You know, if you're a patient in a ward and you have, you know, 98% oxygen saturation, then me putting you on an oxygen infusion is not gonna change your oxygen saturation. You're already close to ceiling levels. You're already close to 100% saturation. But if you're 80% uh, or 70% and I give you oxygen, that's gonna make a big difference. So what if we were to sort of get people closer to a diet that's almost saturated at 99% nutritional? Do you get any benefit from the oxygen mask of caffeine when you place it on? I would love to do that study. I love how you're thinking.

Dr. Rangan Chatterjee 1:08:36 Yeah. Well, let me know if you do it because then we can talk about it again-

Matthew Walker 1:08:39 [laughs]

Dr. Rangan Chatterjee 1:08:39 ... because that would be awesome to find out. But, um, oh,

Dr. Rangan Chatterjee 1:08:43 Matt, there's so much to talk about. We've only got 20 minutes left, so I think let me try and steer this a little bit. I think we should cover, based upon the questions I received, let's cover the trackers, which I think a lot of people wanna know about.

Matthew Walker 1:08:58 Mm.

Dr. Rangan Chatterjee 1:08:58 Let's cover sleep and the immune system, and then we'll definitely finish off with some tips or any new tips that you might have. Of course, if we've got more time, we'll go to other areas. But trackers, you mentioned the Oura Ring before. I don't know if that's a good place to start.

Matthew Walker 1:09:13 Yeah. So I, you know, people often ask me that question, sort of, you know, what's the best sleep tracker? Um, and when they're asking that, they're typically asking it through the lens of the question of accuracy, which is w- what is the best sleep tracker in terms of the one that's most accurate? And I would say that, um, right now, you know, there are a number of, um, sort of gadgets out there. There are wristwatches, there are headbands, there are rings, et cetera. Um, many of them are quite similar if they are tracking your heart rate, your heart rate variability. Um, many of them are similar in terms of their accuracy, so, um, these sort of rings, these wristwatches, et cetera. Um, I should note, by the way, that, um, I wear an Oura Ring. That's my preferred, um, sort of flavor of sleep tracker. And full disclosure, recently, um, I, um, decided to join, um, uh, the scientific advisory board. So take everything I say regarding the Oura Ring with a pinch of salt as a consequence. But I was, I have worn and bought just about every sleep tracker out there, and I'd been wearing the Oura Ring for about two years before I even considered, um, sort of trying to advise the company. And the reason I joined the company and I favor Oura is for the following, um, two reasons. The first is that I think it's just as com- as competitive right now as any other tracker out there in terms of staging your sleep. Most of them right now, if they're tracking your heart rate and heart rate variability, not the things that you put under your bed or the, your phone, those aren't particularly good. But things that you, you know, place on you- yourself, they are about 70% accurate, probably about, you know, 80% accurate in determining, you know, how much total sleep, and then about 70, 40 to 70% accurate in determining light sleep from deep sleep from REM sleep. And I think looking at the data that I'd seen in independent studies, I felt that Oura was as good, if not probably edging into market leader, um, relative to other things, you know, such as Fitbit or the Whoop Strap, um, et cetera. But the thing that really makes me more excited about that is a different way of answering that question through a different lens. It's not just about the accuracy, it's about the adherence and the compliance, and you know this better than anyone as a doctor. You can come up with the most accurate, you know, wonderful intervention to help someone with diabetes or help manage their weight or help lower their blood pressure, and it can be exquisite and near perfect, 100% accurate. But if they don't do it, it's useless. So adherence and compliance is just as important as accuracy. So I think about trackers in these two different verticals. So in other words, it's like a two-by-two matrix. What I want is a tracker that is highly accurate and is also highly adoptable by the user. And so what I mean, I've become very enamored with the idea of unwearables, and the reason I don't really like wristwatches or even headband devices is that when we go to sleep, we take things off. We don't put things on. And as a consequence, that's why when you look at these numbers, and probably some of these companies wouldn't show you these numbers, but the, it, once, you know, they start off with these headbands or these wristwatches, the first week they're tracking their sleep and they're really excited, and then it just drops off. You know, and what you often will say in medicine is what gets measured gets managed. And if you're not wearing it, it doesn't matter how accurate it is, it becomes a useless device But a ring as a form factor, I found personally, you know, many of us will go to sleep with our wedding bands on or rings on. We don't take those off, and they're unobtrusive. And so your compliance to consistently wearing a ring is considerably higher than your compliance to wearing a headband or a chest strap or something that goes on your wrist. So for me, the best sleep tracker is the one that is good in terms of its accuracy, but great in terms of its stickiness. It needs to be a low-friction device, and what I mean by that is, you know, you don't have to worry about charging it every day, you don't have to worry about sort of strapping it on, or when you turn over at night, did you forget to sort of, you know, switch it to nighttime mode and it, you know, flashes in your face and wakes you up? And you just need to be able to, you know, fall into bed and not even think about it. So that's the reason that I, I sort of favor the Oura Ring right now as sort of the, the dish du jour. Um, but again, you know, take, uh, what I'm saying with a grain of salt considering I'm now, you know, an, an advisor to the company. But in truth, I'd been wearing the ring for two years beforehand before I even wanted to, to consider, uh, helping them.

Dr. Rangan Chatterjee 1:14:29 Uh, I mean, I guess on one hand, measuring it, being aware of it allows you to change it. I wonder if there's a downside here as well potentially where we can become obsessed and-

Matthew Walker 1:14:45 Yes

Dr. Rangan Chatterjee 1:14:45 ... start looking too much and start not paying attention to how we feel, but more what does the app or what does the tracker say? Is this something you think we should be concerned about potentially?

Matthew Walker 1:14:59 I do. And in fact, there is some data on this that there is a proportion of users, we don't quite know how big it is, it may be sort of less than 10%, but there's certainly a proportion of people, um, that suffer from what we now call orthosomnia. Now, um, ortho, as, uh, sort of as you will know, but, um, the derivative of that term just simply means straight- straightening. So you've heard of orthodontics or orthopedic, orthopedic, straightening bones, orthodontic, straightening teeth. Well, orthosomnia is this worry about getting your sleep straight, getting it right. And for some people, when they start to use sleep trackers, rather than it being a beneficial force in their life that helps motivate them and helps them make behavioral change, just like you said, with your sleep tracker you can see that when you, you know, consume caffeine or when people consume alcohol, um, it just decimates their REM sleep or their deep sleep, and it's a great behavioral change tool. But for other people, when they start to see that their sleep isn't great or is not what they want, it starts to create anxiety. And the more anxiety that they have, the worse-

Dr. Rangan Chatterjee 1:16:09 Yeah

Matthew Walker 1:16:09 ... that they sleep. And I would say if that is the situation, you know, take that sleep tracker, put it in a drawer, and forget about it for now. Just don't worry 'cause it's, it's only going to make matters worse. And, you know, falling asleep and insomnia in those situations, I often liken it to trying to remember someone's name. The harder you try, the further you push the likelihood of remembering that name away from you, and it's the same way with sleep. The harder that you try and the more anxious you become about not sleeping and the more fretful you become in bed lying awake, the l- you know, the less likely sleep is going to, to, to arrive to you. So just take a break from sleep at that point. Relax. Don't worry about it. Don't worry about all of these health sort of detriments regarding a lack of sleep. There i- everyone has a bad night of sleep, um, but if you're struggling with insomnia, you don't need to struggle. You know, really go and see your GP. There are good tools out there. Um, you don't deserve bad sleep, you don't deserve insomnia, and there are ways to get around it. But sleep trackers, if you're having that experience, do not wear them. Absolutely let go of them.

Dr. Rangan Chatterjee 1:17:25 Yeah. Uh, so I bought an Oura Ring myself in maybe June, July of 2020, and it's been great actually. It's been really fun to see the different stages of sleep. The biggest change I've made, because I was doing a lot of stuff anyway, I think, for years that were, you know, as I sort of surprised how I sleep more, I was doing a lot of the things that I think were helping me, and I wouldn't have said I had a problem per se, but it's when I eat my evening meal, and I eat earlier now. I stop eating two to three hours before bed-

Matthew Walker 1:18:04 Mm

Dr. Rangan Chatterjee 1:18:04 ... and that includes snacking because I saw changes in my heart rate, my readiness score. You could... And for me, because I don't use it all the time, if I'm honest, 'cause I kind of feel I've learnt what I needed to learn. Like, I feel I've been on this growth curve with it, and I've think, "Okay, cool. I kind of think I, I'm good at the moment in terms of what I've learnt from it," but that is the number one change for me. By 7:00 PM, I'm done. Like, I won't-

Matthew Walker 1:18:30 Yeah

Dr. Rangan Chatterjee 1:18:30 ... snack after that. I won't do anything because it impacts the quality and it impacts how much rest I get.

Matthew Walker 1:18:37 And what's striking is that there's actually not a particularly good scientific literature that looks at the timing of food in its distance from your bedtime relative to sleep quality. However, I hear this so much from people when they say that, you know, if they're eating too close to bed, then it will disrupt their sleep quality. And you've had, um, you know, a wonderful, uh, series of podcasts with, uh, Satchin Panda here, who ironically enough, I think when you and I did our first podcast, Satchin is down, uh, in San Diego, um, about a, a seven-hour drive from me here, uh, up in, uh, the northern region of California. Um, he's a circadian sleep researcher sort of, and I'm a, a sleep researcher, he's a circadian, uh, uh, researcher. And we would W- w- we l- love our, each other's work, and, you know, we, we, we're so simpatico, but we never really got the chance to connect. And then lo and behold, one morning when I was in London, just, uh, with Penguin doing publicity for the book, I was out running down by the Thames, and I ran past Sachin.

Dr. Rangan Chatterjee 1:19:43 [laughs]

Matthew Walker 1:19:44 I said, "Sachin, what are you doing here?" So we had to both fly to London to meet, yet we're in the same state here. But he's spoken a lot about how, you know, the digestive tract needs some distance after food consumption in order not to be active and wake you up, particularly with acid reflux. But the other thing, too, I think that we need to do these studies, and as I said, I think you're absolutely right, and the scientific studies will bear this out, um, from front to back. I think the other reason is metabolism, and it comes on to temperature. Because what we know is that when you go to sleep at night, for you to fall asleep and stay asleep, you need to drop your core body temperature by about one degree Celsius to fall asleep and then stay asleep throughout the night. But if you have a large bolus of food right before you go to bed, that will actually be thermogenic. So your core body temperature, because you've just eaten, will actually start to increase, and I think that was, that's an, an interesting sort of potential hypothesis that we need to test. I also think it's the reason why having, if you're going to have a meal before bed, and some people like to have a snack before bed, and that's okay, too. Everyone's different. If you're going to do that, though, try to make it a high-fiber, high-protein meal, but not a high-sugar meal, because sugar in particular is very thermogenic. You know, y- it will increase your body temperature. So, you know, having some, a little bit of Greek yogurt with some, you know, fiber, um, some kind of fibrous material with it, um, that's gonna be a great little pre-bed snack. But don't, don't load it in there. So you're absolutely right.

Dr. Rangan Chatterjee 1:21:28 Yeah. Y- you're tempting me now to try a high-fiber, high-protein snack now and see, s- get the Oura Ring out and actually see if it makes-

Matthew Walker 1:21:34 [laughs]

Dr. Rangan Chatterjee 1:21:34 ... a difference. I'll, I'll let you know what happens there. Matt-

Matthew Walker 1:21:37 Please do

Dr. Rangan Chatterjee 1:21:37 ... let's see if we can get through immune system and some sleep tips-

Matthew Walker 1:21:41 Yes, yeah

Dr. Rangan Chatterjee 1:21:42 ... if possible in the time we have left.

Matthew Walker 1:21:45 Yeah, so, um, I think many of us, of course, are so immune sensitive right now, both [laughs] from a physiological perspective, but also from a mental state perspective. Um, there is a very intimate association between your sleep health and your immune health, and I'll just give some examples to impress upon people how strong this is. Firstly, what we know from a study that was published, uh, a few years ago is that individuals who are sleeping less than seven hours a night are f- almost three times more likely to become infected by the rhinovirus, which is the common cold, relative to those who are getting eight hours or more. We also know in a prospective study, um, in over, um, 70,000 women that those women who were sleeping, um, five hours or less a night, um, were more than 50% more likely to, um, suffer and develop pneumonia, which we know is a critical component of the COVID equation. Why is sleep so great for your immune system? Well, we now know the first thing is that sleep will actually restock the weaponry in your immune arsenal. Sleep stimulates a collection of immune factors. The second great part of sleep is that not only do you create more of those immune factors, but sleep sensitizes your body to those immune, um, factors that you've produced. So when you wake up the next day, you are a more immune, robust individual. You're both greater in terms of your immune system, um, sort of, uh, components, the weaponry, as I, as I sort of mentioned, in your immune arsenal has increased. But also the receptivity of your body to those immune signals has also increased, and that's why you're so much better from an immune perspective when you are sleeping, and that's why you're so worse in terms of a compromised immune system when you're not getting sufficient sleep.

Dr. Rangan Chatterjee 1:24:03 Yeah. Wow. Sleep may well be one of the most important things we can do for our immune system health, and wouldn't it be great to see some more public health messaging around that? Matt-

Matthew Walker 1:24:14 It would

Dr. Rangan Chatterjee 1:24:15 ... sleep tips.

Dr. Rangan Chatterjee 1:24:16 Let's see, what are the most important things for people to think about when it comes to getting more sleep?

Matthew Walker 1:24:24 So I think in our sort of last conversation, we went through sort of the typical sleep hygiene tips of sort of regularity, get some darkness at night, turn o- you know, turn off those screens, but also dim down half of the lights in your house before you, um, go to sleep. Um, the third is temperature that we've spoken about. Get your bedroom temperature to around about 18, 18.5 degrees Celsius is going to be optimal for sleep. Um, not lying in bed awake, we've spoken about that, and then avoiding alcohol and caffeine. Those are all good things, I think, that can, um, sort of help. But, and I'll come onto a caveat there, too. Th- the other tips I have, the first thing is have a wind-down routine. You know, many of us expect inappropriate things of sleep. What I mean by this is we think that sleep should be like a light switch. Now, for some lucky people, that may be the case, and in fact, I would argue that if you really just fall asleep within a minute or so, it's actually pathological. It means that you're not getting enough sleep. You shouldn't fall asleep that quickly. But many of us think that sleep is like a light switch, that we took ourselves into bed, we turn off our light, and then we should be able to turn off our brain and fall asleep just as quickly. Sleep is not like that as a physiological process. Sleep is much more like landing a plane. It takes time to gradually descend down, and you need to build in a routine. You know, with kids, you would never have a kid playing, you know, until right up until their bedtime, then stick them into bed and think that they can fall asleep. It's never gonna happen, you know? They need a wind-down. They need a bath. They need to be read to. You find a wind-down routine for them, and it works wonderfully. Human adults, just like human children, are no different. So have a wind-down routine, and that could be having a bath, or it could be reading for a little bit. It could be doing light stretching, or it could be a meditation. Whatever it is, find out what works for you and stick to it. That's one of the best pieces of advice I can, I can give you. The next thing is that if you are struggling with sleep, remove all clock faces from your bedroom. Looking at a clock if you're struggling with sleep and knowing that it's 4:23 AM in the morning is not gonna do you any favors whatsoever. So let it go. Take- remove all clock faces. Um, another thing is don't lie in bed counting sheep. [laughs] The study has been done, and it actually makes you, uh, have worse sleep. But if you are struggling with sleep and you don't want to get out of bed per my advice, and you don't want to do meditation 'cause that's not your thing, a great tip here is to get your mind off your mind. And [laughs] because one of the reasons that we can't fall asleep is because we start catastrophizing and ruminating, that Rolodex of anxiety. So one trick that they've found that's useful is, um, take yourself on a walk. Think about a walk that you can visualize, you know, it's a walk, uh, in the woods or a walk on the beach, and take yourself off on that walk for 5 or 10 minutes. And then the next thing you realize is that your alarm's going off, and you're waking up in the morning. Um, the, the final thing I would say before the caveat is if you- I would love it if people could keep technology out of their bedroom. I know it's hard. I know it's so, so hard. The last thing that most people touch at night is their phone, and the first thing that they touch in the morning is their phone. And if you can, try just keeping it outside of your bedroom and see if you can hold off until you've brushed your teeth. Just start there. It's the BJ Fogg kind of approach. And then put it in the kitchen and see if you can not touch your phone until you have your first cup of tea, and sort of keep pushing the boat out. But if you have to bring your phone into the bedroom at night, here is the following rule so that you don't use it in bed. You can only use your phone in the bedroom if you're standing up. And what will happen is that after about 5 or 10 minutes of using your phone in your bedroom when it's time for bed and you're standing up, you think, "God, I just don't want to stand up any longer." If you can't stand up using your phone, you need to sit down. Then at that point, you gotta put your phone away, and that's the kind of the hack. The final thing I would say, uh, Rangan, is all of these tips I'm giving sort of, you know, here and, and that we provided on the last podcast, these are tips for people to improve their sleep if you are not suffering from a sleep disorder. And the analogy would be the following. Let's say I'm your sports, your sports coach, and I'm giving you all of these tips to improve your performance, but you've got a broken ankle. No amount of my tips are going to help improve your performance until we get you to a doctor and we get your broken ankle fixed. And it's the same way if you have a sleep disorder. If you have insomnia, if you have sleep apnea, have heavy snoring, none of the tips I'm going to give you are really going to be helpful. You need to go and see your doctor, get that sleep disorder treated, and then come back to these tips.

Dr. Rangan Chatterjee 1:29:48 Matt, so helpful, so clear. Uh, thank you so much once again for making time to come on my podcast.

Matthew Walker 1:29:54 Oh, you're-

Dr. Rangan Chatterjee 1:29:54 I think you-

Matthew Walker 1:29:55 ... ever so welcome.

Dr. Rangan Chatterjee 1:29:56 Matt, honestly, you, you have done such a wonderful job in raising the profile of sleep and its importance, and your work is helping hundreds of thousands of people all around the world. I can't wait till the next time.

Matthew Walker 1:30:11 Aw. It's such a pleasure to speak with you. Um, I feel, um, you know, just I, I'd love next time, uh, I, I come over and all of this pandemic is, is over, let, let's, A, do another one of these if your audience isn't, hasn't lost the will to live because I, [laughs] I came on a second time, but also just spending time. Um, I think we're, we're so like-minded, and it's just lovely to speak with you, and also to speak with someone who has an appreciation of sleep and who's trying to communicate that. Thank you for having me a second time around. Thank you for helping me try and get this message out.

Dr. Rangan Chatterjee 1:30:43 Yeah, my pleasure, Matt, and I can't wait till we, we get together in person. [upbeat music] Hope you enjoyed that conversation. As always, I would recommend that you think about one thing you can take away and apply into your own life immediately. And if you want more tips on sleep, just head over to my website, drchatterjee.com, and you can see a free five-part video series that I've just created all about sleep. Simply pop in your email, and I'll send the videos over to you right away. I want to take a little pause right now and share this conversation with someone in your own network. Do you know someone who struggles with their sleep? Well, why not send them a link to this episode with a personal note? This serves as an act of kindness, which has benefits not just for the other person, but for you as well. And if you're looking for some inspiration for the new year, my brand new book, Feel Great Lose Weight, is available to order right now. It came out just over a week ago. There's already nearly 150 five-star reviews on Amazon. I'm really, really pleased that so many of you have connected with the content in there. Yes, it's written around the topic of losing excess weight, but the truth is that most of the ideas within the book are universal and will help you form new habits, understand your own behaviors better, and ultimately help you live happier and healthier lives. It's available in paperback, e-book, or as an audiobook, which I am narrating. And here's a short clip to give you a little taste. Many people I know eat when they're lonely. Once upon a time, we always ate together. Families and communities would gather at night to enjoy their food as a connected group. When a hunter caught an animal, the meat would be shared. But we're more isolated than ever these days, and researchers know that feelings of severe social separation are rife and rising in the West. If you're feeling lonely and you don't have those rich, meaningful connections in your life, then that may be why you're spending too much time on the sofa eating biscuits and sweets. You feel like you've got a hole in your stomach, but the hole is actually in your heart. Hope you enjoyed that little clip from the audiobook. If you go to the show notes page for this episode on my website, you can see all of the international book links, as well as learning more about Matthew Walker and his work. And new for 2021 is my bite-sized Friday email called Friday Five. It contains five short doses of positivity, articles or books that I'm reading, quotes that I'm thinking about, exciting research I've seen, and so much more. The first one went out last week. Feedback has been wonderful. The goal is for it to be a small yet powerful dose of feel-good to get you ready for every weekend. You can sign up for it at drchatterjee.com forward slash Friday Five. A big thank you to my wife, Vidarta Chatterjee, for producing this week's podcast, and to Richard Hughes for audio engineering. Have a wonderful week. Make sure you have pressed subscribe, and I'll be back in one week's time with my latest conversation. Remember, you are the architects of your own health. Making lifestyle change is always worth it, because when you feel better, you live more.