The secrets of good sleep | Professor Matt Walker

[Music] welcome to Zoe science and nutrition we're World leading scientists explain how their research can improve your health [Music] we all know how good it feels to drift into deep sleep to explore the land of dreams take stock of the day's experiences and wake up refreshed [Music] the positive effects of a good night's sleep stretch into every aspect of Our Lives we feel energetic focused and ready to take on the day's challenges but the long-term effects of bad sleep are less known and it turns out they have a huge impact on our health and even

how long we live Alzheimer's cancer obesity and diabetes are all linked to poor sleep so what is the latest science tell us about how we can improve our sleep to give us more energy and better health and is it true that how we sleep changes how our body responds to food [Music] to find out we're joined by Sleep expert Matthew Walker professor of neuroscience at UC Berkeley and founder of the center for human sleep science Matt and his team are currently working with Zoe scientists to research the link between sleep nutrition and health the first

scientific paper from our work together has just been published by Nature Communications explaining why you feel energetic or tired when you wake up you can find the link in our show notes Matt's best-selling book why we sleep transformed my own attitude to sleep five years later I still follow much of his guidance I hope you will find Matt's actionable advice as powerful as I have [Music] thank you for joining me today I really enjoyed your book you know why we sleep which I first read quite a few years ago now when it first came out

and I have to admit I'm not sure I've said this to you before but I drove my wife crazy turning our bedroom into a cave afterwards so she definitely knows who you are even though she hasn't yet met probably for all the wrong reasons but at least I anoint you as a sleep Ambassador for what you've been doing Jonathan well thank you I think uh as always it's a bit like with Zoe and nutrition you know I now get her so long about this and eventually gets into it and then she becomes more obsessive than

me so uh she's on that path with sleep but anyway look it's great to have you here talking about sleep both your research and I think we're also going to touch on some of the research that you're working on together with Zoe now we have a sort of tradition here on the podcast we always like to start with a quick fire round of questions from our listeners and the rules are really simple you can say yes or no or a one sentence answer but no more and we know that scientists always find this challenging so

are you ready for me to kick off I'm ready for the challenge all right so first question can bad sleep kill yes in multiple different ways through multiple different diseases I know we're going to talk more about that okay is it more important to exercise than to sleep well I would say sleep is the foundation on which exercise and nutrition sits it's not a third pillar it's the foundation for those two other things and I'm guessing that the people listening to this call waking up at five in the morning to exercise we'll talk a little

bit about whether that's a good idea I mean we will all right is a short nap in the day okay mostly yes if you're suffering from insomnia no can what we eat affect how we sleep yes I have a small child Matt I get woken up in the night is my health doomed no simply get sleep whenever you can get it across the day or the night during that time period of ownership of a young one all right that's great advice which also sometimes is hard to follow so Matt what's the biggest myth about sleep

that most people still believe there are so many myths but I think one of the fun myths that has been busted is that counting sheep will help you fall asleep and there's a great study done here at UC Berkeley and it wasn't done by me as to by a colleague of mine and what they found is that counting sheep not only didn't make you fall asleep any faster it actually took you longer to fall asleep when you were counting sheep but what they did find was something interesting there is an alternative mental strategy that strategy

is taking yourself on a mental walk and so think about a walk that you know really well maybe it's a walk in the woods or in the forest or a hike or a walk on the beach and then try to really visualize that to the point of this is me leaving my front door I'm walking down the steps off I go and if you do it in granular detail and move yourself through it the next thing you remember is your alarm going off the next morning because you've fallen asleep and it seems to be a

quite effective tool so that's one of the many many myths that we can bust regarding sleep brilliant thank you Matt and look why don't we actually just start right at the beginning there about what is sleep and I know it sounds like a sort of crazy question right because we all sleep I think it remains sort of one of the more mysterious Key activities that happen in a human being so could you just sort of kick off with us there yeah it's bloody bizarre isn't it I mean you know we close our eyes and then

we think that we essentially lose Consciousness and that our body just lies dormant and then seven to nine hours later we wake up now that is so understandable and if I didn't know what I know about sleep I would think the same and as a consequence I perhaps would say well look what's the big deal of losing 30 minutes or an hour here or the you know or just going down to six hours because I'm a busy person or five and a half hours because really I'm just missing out on my body getting some rest

and my mind is not really doing much nothing further from the truth is the actual fact of it your brain is incredibly active during stages of sleep in fact during some stages it's up to 30 percent more active than when you're awake more than 30 active than when I'm away that's that's crazy yeah in some parts of your brain of 30 more active in some stages of sleep than when you're awake and then downstairs in your body there is a radical overhaul there is a it's like hitting the reset button on your Wi-Fi router but

it just takes seven to nine hours to do and let me just take a step back though because I haven't really answered your question what is sleep sleep in human beings in fact in all mammalian species is separated into two main types on the one hand we have something called non-rapid eye movement sleep non-rem sleep on the other hand we have rapid eye movement sleep or REM sleep and REM sleep is the principal stage in which we dream now it turns out that non-rem sleep is further subdivided into four separate substages that unimaginatively called stages

one through four increasing in their depth so stages three and four that's the deep sleep that we discuss and then stages one and two of non-rem that's light non sorry that's light uh sleep so you may have seen this in some of your sleep trackers where it says were you awake in light sleep deep sleep or REM sleep now those two types of sleep non-rem and RAM will end up playing out in a 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 creating the standard 90-minute cycling architecture of human sleep on average in most people what's interesting however is that the balance the sort of the cocktail mixer distribution of non-rem and REM within those 90-minute Cycles changes as you move across the night what I mean by that is in the first half of your night the majority of those 90 minute Cycles is comprised of lots of deep non-rem sleep and very little REM sleep but when you push through to the second half of the night now that shifts and instead you get much

more REM sleep and very little deep sleep and Matt what's all of this for so I mean we're definitely going to picture that it's a lot more complex than I guess uh most of us imagine which is I always sort of felt oh you go to sleep you wake up it's sort of annoying right like all those hours when you could do something better I think you're starting to paint this picture of a lot of complexity why is any of this happening learning memory emotional brain regulation brain plasticity downstairs and in the body and overhaul

of your cardiovascular system a replenishing of your immune system a re-regulation of all of your hormonal systems in fact 50 years ago we used to ask the question why do we sleep and the crass answer at the time was that we sleep to cure sleepiness which tells you nothing about you know the meaningfulness of sleep um Now 50 years later we've had to upend the question we now have to ask is there any major operation of your brain or is there any major physiological system in your body that isn't wonderfully enhanced when you get sleep

or demonstrably impaired when you don't get enough and so far the answer seems to be no that's amazing and so how does that tie in you're describing these different stages are they linked to particular elements of the way in which sleep is sort of creating all of these benefits for us very much so so what we've learned is that all of those stages even some of the light forms of non-rem sleep all of those stages of sleep are important and so sometimes people will come up to me and say how do I get more deep

sleep or how do I get more REM sleep and my question to them usually is why do you want to get more REM sleep or deep sleep and they'll say well isn't that the good stuff and it turns out and it's all good stuff just that different stages of sleep will do different things for your brain and your body at different times of night and we can't shortchange the brain on any one of those stages without suffering some kind of deleterious impairment so you need all of these different stages that you're describing because they're each

doing different things for both our mind and sort of the rest of our body is that what you're saying that correct and when you think about it from an evolutionary perspective of course that must be the case because when we're asleep sleep is the most idiotic of all you know inventions because when you're asleep you're not finding a mate you're not finding food you're not reproducing you're not caring for your young and worse You're vulnerable to predation yeah I know I hadn't really thought about it that much but you're right of course being asleep is

a terrible place to be isn't it and Matt do we understand what is going on in this REM stage we do REM sleep is associated with dreaming but dreaming may just be an Epi phenomenon you could imagine that dreaming is like a light bulb the reason that we create the apparatus of the light bulb is to create light but it turns out when you produce light in that way you also produce heat it was never the reason for the light bulb it's just what happens when you produce light in that way and the same could

be true for dreaming that the reason that the brain created this thing called REM sleep was to serve lots of different functions but when you do create REM sleep in the way that we have you also get this byproduct called Dreaming it's just an Epi phenomenon well now we know that REM sleep and dreaming itself actually are all functional the things that we've discovered are at least twofold the first is that REM sleep provides a form of overnight therapy it's emotional first aid and it's during dream sleep and the particular brain chemistry of dream sleep

where we reactivate emotional experiences and events that we've had during the day or even in past years or months and we re sort of process that information and in doing so it almost is as though REM sleep is a nocturnal soothing bomb that takes the sharp edges off those difficult painful experiences so you wake up the next day and you feel better about them so in other words it's not time that heals all wounds but it's time during dream sleep that provides emotional convalescence that's amazing so this idea that you know what if I sleep

on this thing I might feel better in the morning which is I think my mother used to always say to me you know go to sleep you'll feel better in the morning correct you're saying that was real science that's extraordinary yeah and in fact there's a wonderful quote by the American entrepreneur e Joseph kossman who once said the best bridge between Despair and Hope is a good night of sleep that's exactly what we found so that's one function of of dreaming of REM sleep the second function however relates to your learning and memory abilities and

what we found is that deep non-remp sleep is the stage of sleep where we essentially cement new memories into the brain it's like hitting the save button on that document but when we do that for all of the information that we've been learning is during deep sleep and it takes a little bit longer than hitting the save button but what does REM sleep do then well it turns out that REM sleep is a form of almost informational alchemy that REM sleep then takes all of the information that you've recently learned and starts colliding it and

interconnecting it with all of your past back catalog of experience and creates new and novel links and associations so that you wake up the next morning with a revised mind-wide web of associations that is now capable of divining solutions to previously impenetrable problems so this is the sort of Eureka moment when you wake up the next day and suddenly you know it all sort of makes sense even though yesterday you know you couldn't really figure out the solution to whatever the problem was that's exactly right I mean think about it no one has ever told

you Jonathan that you should really stay awake on a problem you know instead they tell you to sleep not a problem it's amazing and I think we're going to a bit more about the impact of good and bad sleep just before we move off this topic because I I think I can keep asking you questions around exactly how sleep Works forever but how do you figure this out in your lab you know how do you actually understand what's going on given that you know this is very different from many of the topics that we look

at at Zoe where you know you're constantly measuring blood for example you can see the changes but how are we able to get these sort of deep insights that you're talking about we use a vast array of different technology my sleep center here at UC Berkeley so we will measure your sleep with what's called high density EEG which means I'm going to stick hundreds of electrodes all over your head you look like the spaghetti monster and that allows us to pick up all of the special brain waves that are going on during the different stages

of sleep and you have to shave my hair to do that or am I allowed to keep that on Matt you would think but no we don't thankfully that's that's good it's somewhat easy to do all right then I'm signed up yeah so yeah don't worry you will keep uh your um wonderful her and but then we also use a whole variety of other Technologies we use MRI uh particularly to look deep into the brain and look at the patterns of brain activity that are changing when you're in and out of different stages of sleep

we also look at how your brain has changed before and after a night of sleep we use special pet scans in a lot of our work which I think we'll discuss on aging and dementia to look at different Alzheimer's disease pathology buildup because of insufficient sleep and then we use lots of the peripheral markers that you've been describing we measure blood so we look at lots of inflammatory factors for example in blood we also measure other aspects we measure your cardiovascular system we measure hormonal systems we measure your thermoregulatory system as well and at this

stage there's probably almost not one major system within your body that we're not really measuring in the laboratory and so I think that one of the things you're really passionate about is what happens when people don't sleep enough right Matt yeah so can you talk a bit about this because I think we do live in this world where because of electric light because of digital devices we no longer sort of run out of anything interesting to do after it gets dark and therefore probably you know clearly just sleep as much as our body wants most

of us have to work quite hard in fact to get as much sleep as I think we would naturally do apart from maybe my teenage son he's just fine if I leave him alone so what happens to people if they don't sleep enough so downstairs in the body we know that short sleep or insufficient sleep will change your cardiovascular system for the worse it will increase your blood pressure it will increase the speeding contraction of your heart and it will reduce which is not a good thing something called your heart rate variability and so firstly

we see significant impacts on your cardiovascular system and this is the reason why short sleep across the lifespan increases a whole collection of cardiovascular disease features things such as atherosclerosis and we published a paper on this recently that having just poor quality sleep and fragmented sleep increases inflammation and that inflammation then leads to the buildup of plaques in your arteries and that leads to cardiovascular disease the next thing we speak about is the immune system there is a very intimate association between your sleep health and your immune health for example we know that individuals who

we've done some of these experiments as well if you limit someone to just four hours of sleep for one single night there is a 70 drop in critical anti-cancer fighting immune cells called natural killer cells and so that's you know quite a concerning state of immune deficiency after one short bite of sleep and that's just one night of short sleep yeah and we also know that for example and we've just got the data through for covert in the same is true here but if you are not getting sufficient sleep in the week before you get

your flu shot you will only produce 50 of the normal antibody response therefore rendering that vaccination you know far less effective if not not effective at all I think the other big finding that's burst onto the scene and I think it's probably the most exciting finding recently in sleep science is the link between a lack of sleep and Alzheimer's disease and we do a large amount of this we have multiple large research programs looking at this at my sleep center what we firstly understood is that people who don't sleep enough who sleep six hours or

less or people with insomnia or people with a sleep disorder called Sleep Apnea all of those people have a significantly higher risk of developing Alzheimer's disease in later life now the problem is that that's just correlational that's not causal and so correlation went in search of causation and we found the evidence both in animal studies and in humans for example if you take a healthy human and you deprive them you selectively deprive them of either just their deep sleep or you deprive them of sleep for an entire night the next day we see an immediate

build up in the toxic proteins associated with Alzheimer's disease called beta amyloid and Tau protein and we see that circulating in your bloodstream circulating in your cerebral spinal fluid and using special brain scans we've been able to see that build up in your brain itself so that was a causal demonstration that a lack of sleep is associated with a buildup of Alzheimer's protein reverse that question though if a lack of sleep increases your Alzheimer's disease proteins then what is it about sleep when you get it that de-escalates those proteins and de-risks you from the disease

of Alzheimer's well we then subsequently find and this was a finding by making netigard at the University of Rochester she found that the brain has a cleansing system now we knew that the body had one called the lymphatic system but we actually didn't think the brain had its own cleansing system but it does but it's called the glymphatic system named after the glial cells that make it up but then we made more discoveries which is that that cleansing system in the brain that sewage system essentially isn't always switched on in high flow volume during the

24 hour period in fact it's only during sleep and specifically during deep sleep that the brain switches on that cleansing system and washes away all of the metabolic detritus that has been building up during the day and it's crass and it's hyperbolic but you could say certainly from a biochemical perspective wakefulness is low-level brain damage and what we've now discovered is that sleep is your sanitary salvation and so it's good night sleep clean as it were it's a power cleanse for the brain there are definitely some interesting analogies elsewhere right like so I guess if

you think about muscles we all know I guess from people talk about training that you know actually the act of using muscles causes damage and that the rest and Recovery is Central we discuss that you know areas that I I spend more time on around the guts like how important it's now become clear that you need to leave long periods of time for the gut also to recover and that's partly to do the microbiome but partly towards these processes so it's really interesting that across all these different areas of the body you're seeing the same

thing in the brain and that does sound a bit like my mother saying well you need to have a rest right you need to let your your mind rest says funny also how some of these things feel very similar to sort of traditional advice that our parents and grandparents would have given us which maybe have become harder to follow now that we have all these great devices that can keep us up all night yeah I often say that really all I do as a sleep researcher of the past 20 or so years is put the

science behind everything that your mother ever told you about sleep so well I've always believed that doing what your mother tells you is a good idea even if I don't always actually achieve it so you know that's that's relationship yeah but let me come back to yeah the stuff that we're doing together I mean it's incredibly exciting because you know with a lot of the studies that we and other colleagues have done in the field when we measure your sleep we typically will measure your sleep for just a night in the laboratory because it's difficult

to constantly track individual humans you know night after night after night it's especially difficult to track large numbers of them from one night to the next to the next to the next and then it's even harder to in addition be measuring lots of changes in their brain and their body as a consequence of that ongoing night tonight sleep evaluation meaning that we know a lot what we call cross-sectionally so we just take a large group of people we do one night of sleep recording we measure changes the next day and we show that there's these

associations what that doesn't really tell you however it is what is the consequence within an individual of variability in their sleep across weeks if not months and that's a fundamental question because that's the way most of us live in our lives so what I'm saying is that we've not really understood what inter-individual differences are within an individual over time as their sleep fluctuates what can we learn about that and how does that relate to things such as the metabolic system and their immune system and they've got microbiome that's the type of work that we're able

to do in the Zoe collaboration and then we're also able to look at genetics because of course as you've mentioned before on the podcast there is a remarkable set of twins within the large data set which gives us the ability to look at lots of different things but one of them is genetic heritability and so that is very powerful too and and I can mention if you'd like one finding that I was soon going to be publishing one of the most fundamental questions that we wanted to ask was the following how will you wake up

tomorrow morning and secondly how will you sustain that wakefulness across the day what is it about your sleep or your food or your genes that determines how well you wake up every day and how able you are to stay awake and you'd think that we would know the answer to that question we didn't and we were able to answer it with the data set and so looking at over a thousand healthy individuals which also contained a large number of both identical and fraternal twins and what we found is that how well you wake up the

next day has nothing to do with how much sleep that you get relative to the standard population recommended average instead it was how if you slept longer relative to your own typical average amount of sleep then you wake up more effectively it takes you a shorter amount of time to wake up the engine heats up quicker in terms of operating temperature which is what we call overcoming sleep inertia and then you're far better at sustaining that wakefulness across the day if you've slept longer than is your normal the second part is that we found it's

not just about your sleep it's also about your food and expressly your breakfast and what we find is that breakfasts that contain slightly higher amounts of fat and fiber but low amounts of simple sugar that type of a breakfast predicted a far superior ability to wake up and then stay awake across the day the next thing we we found and you would think that you know just the innate levels of how alert someone is you know you can find some people who just seem to have crazy energy that you know each and every day and

other people who are just a bit more sort of Baseline relaxed you would think that that means that it's strongly genetic well we did a twin per analysis and we demonstrated that using this data set genetics only have a very small contribution in determining how well you can wake up and stay awake across the day and I think that that's actually very encouraging because it means that you're not bound to a predetermined genetic fate that most of how well you feel when you wake up every day and stay awake across the day is determined by

non-genetic in other words modifiable influential factors and I think that is incredibly exciting right both decided that it's personalized it's not just one answer for everybody but people are different but also I think we see this across a lot of our research that you're less Locked In by your genes and I think many of us were led to believe over the last sort of 40 or so years and I think that's really reassuring right because it suggests there's still things you can do to change this so much so that's exactly the message that how you

sleep and how you eat each and every day will decide how well you wake up and feel awake across each and every day and do you see changes you know across time and I think one of the topics that you know we had a lot of questions from our listeners about was around menopause which is obviously a really big change that we we touch on in a lot of places is that something that's well studied and and what's going on there personally I don't think it's the need uh anyone near enough but we know that

there are marked changes during that what we call the sort of the perimenopausal period so during menopause and both before and after it there are really significant increases in sleep disturbance sleep becomes more fragmented when you wake up people will find it harder to fall back asleep and then there are the temperature swings the temperature changes these hot flashes that people will experience why is that a problem well it's a problem at night because it turns out you your brain and your body need to drop their core temperature by about one degree Celsius or about

two to three degrees Fahrenheit for you to fall asleep and stay asleep and that's the reason you will always find it easier to fall asleep in a room that's too cold than too hot because the room that's too cold is taking in the right temperature direction for good sleep but if you're having these changes inside of the body and the brain that create a thermogenic effect that create these bursts of heat that we call these hot flashes no wonder you're struggling to stay asleep so menopause is certainly one of those time periods where we see

sleep disruption and then also just as we get older unfortunately we know that probably the one of the cognitive Hallmarks of getting older of course is that our learning and memory abilities begin to fade and Decline and that's been known for a long time what we've also discovered though is that one of the the most reliable physiological signatures of Aging is that your sleep gets worse and not just any type of sleep by the way it's particularly that deep quality of sleep that we were describing before which is actually essential for some of the cardiovascular

functions for some of the learning and memory functions for some of the immune system functions all of which change with aging that's the type of sleep that declines most precipitously as we get older and the worrying thing is by the way that great sleep depression for deep sleep at least we can start to measure it happening in your mid to late 30s which is exciting for me because that means that's an opportunity for prevention I think you know this is one of the goals of the Zoe project too of course is that we have a

model of Sitka and we don't have a model of healthcare and we don't really understand the question of rather than what happens when a human being goes wrong how do you treat that disease how before you ever get to that stage do you maintain a human in the right healthy direction and that is a model of healthcare rather than sick which is what we have now in modern societies and I think you know this is something I you know I I believe in passionately and um you know it's so clear that sleep is one of

these Central pillars right that if you get right can really improve your long-term Health um and and I guess I stopped your mid-fly there Matt but I I just say yes we're incredibly exciting obviously we think nutrition is very important part of this but ultimately this is about understanding you know the set of things that you can do before you're really sick to try and make sure actually you put that off for for as long as possible that's exactly right and that's why I think this you know in some ways it's depressing to know that

it's in the mail for all of us you know I'm now coming solidly into the foothills of middle age myself and um I've already seen the changes in my sleep I can notice them but what if we can do things that could intervene and actually really prevent that decline of Deep Sleep could we for example even bend the arrow of Alzheimer's disease risk down on itself by way of superior sleep intervention in midlife that's one of the things that we're very excited about trying to do it at my sleep center and I think it's a

brilliant transition to the last topic and I would say just personally I have really noticed I'm in in my late 40s now that I do not sleep as well as I used to I used to be someone I would consider myself a really good sleeper and there's no doubt that I'm more easily Disturbed that when I Disturbed I find it harder to go back to sleep and this is even after using all of your great tips but should we transition to that because we always like to make sure we give actionable advice and I know

you have some really great advice for people listening to this who are now saying you know what maybe I didn't take sleep as seriously as I should have done now I want to take it really seriously how can I go and get better sleep what would your advice be met no I think there's a couple of General tips and you can find most of these on the internet too but it's good to go over them the first thing is regularity I would say if you could just focus on one thing go to bed at the

same time wake up at the same time no matter whether it's the weekday or the weekend and I'm pretty religious like this you you know and not because I want to be a poster child for good sleep it's selfish you know if you knew everything I knew about sleep and how important it it is you wouldn't do anything different than priority sizing your sleep and I do so I would say make sure you're getting somewhere between a seven to nine hour opportunity find out what is innately correct for you which is called your chronotype are

you a morning type evening type of somewhere in between and you need to sleep in harmony with your chronotype to get the best sleep so I'm somewhere in the middle just like the rest of my personality I'm quite vanilla in terms of my chronotype so you either a morning type evening type or a neutral and I'm mostly in neutral I'm kind of somewhere between an 11 to 11 30 kind of you know 7 30 7 45 wake up time which puts me in the neutral category if I were to go to bed um you know

at 9 00 pm and then wake up eight hours later or I were to go to bed at 4 00 am and wake up eight hours later versus my natural eight hour sleep window well it's eight hours so what's the difference that there's surely there's no difference well there's a big difference because in one of those three scenarios I will have been sleeping in sync with what my biological rhythms want me to do and the other times I will be out of sync and I won't sleep as well but the first message is regularity and

Matt just a question because I know that we'll get a flurry of these questions afterwards how do you find out your chronotypes so that you know that you can be sleeping in in line with that if you want to do the detailed assessment you can go on to Google and you can search for something called the m e q which stands for morningness eveningness questionnaire takes you about three or four minutes to fill out and then you'll get a score and that score will tell you um in fact we really use in sleep Science five

categories extreme morning type morning type neutral evening type extreme evening type and it will kind of bucket you into one of these flavors the other way you could really do it though which is kind of like my quick rule of thumb and it's just a rule of thumb it's not really a rule let me ask you the following question if you're on a desert island nothing to wake up for no precious no one to wake up for no work what time do you think you would like to go to bed and what time do you

think you would like to wake up and the answer to that question is usually very different than currently when you have to go to bed and when you have to wake up and that mismatch is the misalignment between how you are forced to sleep versus how you are biologically designed to sleep so that's another way that you can sort of answer the question and it's relevant by the way some people come to me and say I've got vicious insomnia I get into bed and I cannot fall asleep for the first hour or hour and a

half and then we go through this exercise of figuring out their chronotype and what you realize is that they're going to bed at 10 pm because they have to wake up at six to go to work and in fact they're much more of an evening type they would normally like to go to bed at maybe 12 12 30. and so they don't necessarily have insomnia they have this mismatch between their chronotype and when they start sleeping a little bit closer to their natural sweet spot they sleep better so it is relevant to know your grown

type that's fantastic and we will provide links in the show notes to the the questionnaire for anyone who's listening to this and make sure that it's the right one yeah and then other than that I would just probably quickly go through a few others um temperature we've already spoken about um keeping your bedroom cool aim for around about 65 to 67 degrees Fahrenheit or around about what is that 18 18.4 ish degrees Celsius I know it sounds cold but cold it must be you can keep your feet warm hot water bottles socks that's fine but

the ambient must be cold and that's colder than many people keep their rooms today right it is yeah most people will come home they'll set you know have this ambient temperature of you know 70 72 degrees in the house and then they leave that same thermostat setting for the night and we need to cool down at night so keep temperature in mind light is another thing we are a dark deprived Society in our modern era and we need Darkness at night to trigger the release of a sleep hormone called melatonin and so as a tip

I don't like the word hack but as a tip try doing the following experiment in the last hour before your bed so set an alarm on your phone or on your home device say you know set alarm for and whatever time it is now before bed and in that last hour dimmed down half of the lights even more of the lights if you can dim down half of the lights in all of your house and you will be surprised at how sleepy that increased Darkness will make you feel and what that tells you is that

normally you are suppressing the release of this sleepiness hormone melatonin or it's a sleep timing hormone really when you are bathed in electric light at night so light is another one the final two things I would mention alcohol and caffeine I know I know I'm sorry this is bad news yeah you're a bit depressing on this one Matt I have to say but I think you should tell everybody so that they get all the facts well I'm much more bullish now you know some people sometimes on different podcasts when I'm interviewed will say you know

what have you changed your mind on in the last five years I've changed my tune on on coffee I would say drink coffee because the health benefits that have been associated with coffee are profound and very reliable but here when it comes to sleep the dose and the timing make the Poison by the way the reason that coffee is associated with health benefits has nothing to do with the caffeine the reason is because the Coffee Bean contains a whopping dose of antioxidants and because most people and you know this better than than most of us

Jonathan most people in the western world are deficient in their dietary intake and the way that most people get their daily dose of antioxidants is through their cups of coffee and that's why coffee is associated with health benefits case in point you get very similar health benefits for decaffeinated coffee so it's not the caffeine it's the Coffee Bean itself but I would say the dose and the timing make the poison try to limit yourself to two cups on average maybe three but the critical thing is cut yourself off at least 12 hours before you expect

to go to bed that's a good rule of thumb and I would say just on that one I'm actually more of a tea addict than uh than coffee but I have definitely discovered that this timing with the caffeine is important and I now cut myself off I think this is something you can sort of figure out for yourself Matt a bit right because there's a lot of personal variation in caffeine response isn't there yeah there is and we know the genes that change the clearance the speed of clearance caffeine but in my case that means

I need to stop by about two or three o'clock in the afternoon and if I go later then sure enough you know it affects my sleep and sometimes also it can even mean you wake up again right in the night and then you can't go back to sleep so it's a bit more complicated than I I had imagined yeah both make it harder to fall asleep than it fragments your sleep but the other thing that's pernicious about caffeine some people will say look I'm one of those individuals and they could be because they clear caffeine

very quickly but not quick enough as we'll see they'll say I can have an espresso with dinner and I fall asleep and I stay asleep and I'm just fine even if that's true caffeine can actually decrease the amount of deep sleep that you have by somewhere between 12 to 15 percent it depends on the dose of caffeine we've done this in our laboratory now to reduce your deep sleep by 15 I would have to age you by about you know 10 to 12 years or you can just do it every night with an espresso it

is a little bit right you know be be thoughtful hey what about alcohol yeah you know many people when they're struggling with sleep will turn to alcohol as a quote-unquote sleep aid unfortunately it is anything but a sleep aid alcohol isn't a class of drugs that we call the sedatives and sedation is not sleep so when you have a couple of nightcaps people say look I always fall asleep faster if I've had a few drinks in the evening you're not really falling asleep faster you're just losing Consciousness more quickly and that's the first problem alcohol

is a sedative the second is that alcohol will fragment your sleep like caffeine but through a different chemical mechanism so you wake up many more times throughout the night but the problem is you typically don't remember those Awakenings so the next morning you wake up you feel understood and unrefreshed but you don't remember waking up and so you don't put two and two together the final reason that alcohol is not great for your sleep is that it is quite potent at suppressing your REM sleep or your dream sleep and we know that dream sleep as

we've spoken about has lots of benefits of the brain it's critical for the body too REM sleep is the peak time during the 24-hour period when men and women release their Peak levels of testosterone for example so we need REM sleep so I'm very nervous as a scientist to tell anyone how to live their life I don't think I have any business doing that what I'm here to do as a scientist is simply impart the knowledge so that you can then make an informed Choice as to how you want to live your life and of

course my goodness when it comes to cups of coffee and you know having a drink now and again life is to be lived for goodness sake so don't get puritanical about it but just know the evidence and know that there can be consequences by the way I would say that with alcohol the politically incorrect advice that I would never offer you would be go to the pub in the morning and that way the alcohol is out your system by the evening and then you'll be just fine but I would never say such a thing on

a on a health podcast and we did a whole podcast on alcohol and I think it's very interesting topic but I think the impact on sleep is clearly one of the big downsides and Matt one thing that you haven't mentioned but it was so influential on me was about making your room like a cave so you don't get woken up in the morning is that something that still you believe is really important yeah very much so this this is temperature so it's not just about temperature but it also combines the the third tip I mentioned

which is Darkness so keeping your bedroom cool and dark and then you know if you need to you can use earplugs or sound machine we don't know too much about sound machines whether they're helpful or helpful to sleep right now I think for the most part they seem to be mostly benign just before we wrap it up I think one thing I realized you haven't mentioned is screens and that comes up quite a lot yeah yeah it's a good question you know this comes to the the light issue again particularly light exposure at night and

unfortunately our screens are enriched in the blue LED light spectrum which is the worst for our melatonin levels it suppresses it most powerfully I would say that in probably over 50 to 60 percent of the studies looking at Blue Light screens they have an impact on sleep but some of them have not found a robust effect what we do now know is that those devices perhaps the greater detrimental impact on sleep is not necessarily the light but they're activating engagement because when you're on these devices particularly your phone it is designed to capture your attention

make you alert and keep you awake and sustained and engaged and many people will be what we call Sleep procrastinating where they are perfectly tired but they're so engaged with their device that they can't put it down that seems to be if anything it's this alertness that actually masks otherwise very strong sleepiness so my rule of thumb again not to get puritanical it that Genie of technology is out the bottle and it's not going back in anytime soon no matter what I say so you know use your phones and your screens just keep it in

mind that they can have an impact on your sleep and the rule of thumb I much prefer people to keep their phones out of their bedroom if you absolutely have to take it into the bedroom here's the rule you can only use it in the bedroom standing up I hadn't heard that one before yeah it's it's really interesting you kind of think okay after about five or six minutes I'm just gonna sit down on the bed no at that point that's the rule you're done put the phone away that's brilliant and and I have to

say keeping out of the bedroom is one of the things that I've become quite strict about but it's it's not an easy thing always to uh to carry out I would like to just quickly wrap up as we always do and make sure that summarize what's been as always a very wide-ranging conversation so I think firstly you know the big message is sleep is incredibly important you need your sort of seven to nine hours whatever it is for you and if you don't it has these really profound Health impacts we talked a little bit about

the studies that we've been collaborating on to together and this really exciting new paper that's be coming out shortly about how do we wake up every day how are you able to stay awake and about how different each of us are we talked a little bit about sleep disturbance around menopause you gave us a bunch of tips regularity finding out your chronotype getting your room colder finding a way to get your room a lot darker both when you go to sleep and when you wake up and then I think you've got a little softer on

caffeine and alcohol than perhaps when I read the book a few years ago but in general coffee is probably fine but make sure it's long before you go to sleep alcohol I think you're basically saying you know it's it's never probably really good for you but bear that in mind and in terms of screens if you are going to bring them into the bedroom you have to stand up great summary Matt it was a real pleasure and we look forward to talking again in the future I hope with the next paper that we bring out

sounds good take care thank you for hosting me Jonathan I really appreciate it and thanks for the collaboration that we have I think it's it's immensely powerful and it's a privileged data set so thanks very much you're welcome thank you Matt bye-bye bye thank you to Matt Walker for joining me on Zoe's science and nutrition today we hope you enjoyed today's episode if you did please be sure to subscribe and leave us a review we do read all the feedback if this episode left you the questions please send them in on Instagram or Facebook and

we'll try to answer them in a future episode and Zoe we want to improve the health of millions by understanding the right food for each of us to improve our health and manage our weight each member starts with an at-home test comparing them with participants in the world's largest nutrition science study if you're interested in learning more about Zoe you can head to join zoe.com podcast and get 10 off your personalized nutrition program as always I'm your host Jonathan Wolfe Zoe science and nutrition is produced by Fascinate Productions with support from Sharon feder yeah like

Ewings Martin and Alex Jones here at Zoe see you next time