7 How to protect your sleep, Prof Russell Foster CBE, FRSB, FMedSci, FRS

0:00We're on to day seven of our 12 days of Christmas. We have probably lost track of time. We don't know what day it is, let alone what time it is. But what we are hoping for is to catch up on some sleep. In this episode, Professor Russell Foster breaks down the science of sleep and why poor sleep quality undermines decision-making, metabolism and mental health. From the dangers of self-medicating with alcohol to the myths around catching up on sleep, Russell explains what's really happening in the brain when we don't rest properly. This is a clear, evidence-led conversation about circadian rhythms, morning light, anxiety and simple interventions, including when a short nap can genuinely improve cognitive performance.

0:43Thank you, Russell, so much for your time today. It's great to have you on How to Start Up. It'd be wonderful if you could give a bit of a background as to who you are and your profession. Well, I'm really delighted to join you. I'm Russell Foster. I'm Professor of Circadian Neuroscience at the University of Oxford, and I'm the Director of the Sleep and Circadian Neuroscience Institute, and I'm also head of the Nuffield Laboratory of Ophthalmology. And for almost 40 years now, I've been working on how circadian rhythms and sleep are generated, and particularly how they're regulated by light. And more recently, it's been taking that fundamental science and placing it into a sort of a translational context.

1:23So the fundamental science is now being applied to the health sector and a variety of other sectors too. And we should also mention you've written an incredibly interesting book about the subject. And given that not just business owners or founders sleep, everyone sleeps and everyone breathes and everyone needs to drink water. But sleep is such an important part. Is it even possible to explain why sleep is so important to us? Well, I think for so long we've marginalised sleep. We've sort of thought of it as this luxury or indulgence. And in fact, those of us who remember the 80s, people would bounce in and say, oh, I've done another all night, you know, aren't I great?

2:03As if sleep was some sort of an illness that needs a cure. And what's really happened, I suppose, over the past 20, 30 years is we've realized that sleep is an absolutely fundamental and essential part of our biology. The quality of our sleep defines the quality of our wake and our consciousness. It defines how we interact with other people. It defines our sense of humour. There's so much that it does. And it is not an indulgence or a luxury, and we need to embrace it and find ways of embracing sleep. I think this is something I've learned the hard way that when you start a business and you're doing something for the very first time, in fact, 90 % of your day is inaugural.

2:41It's the first time you've ever built a website or worked out your payment terms or tried to invoice somebody or find a client. Time is precious. There are 24 hours in our day that have been talked to us that 24 hours is the day in the seven days in the week. You, as a new founder, tend to go and go and go and go and go until things are done, but then realizing things are never done. Why should we factor in a time allowance for sleep in that working day? Yeah, I think it's so important, particularly when setting up a business. So I think we've kind of defined sleep on the basis of what happens to you if you don't get it.

3:18And perhaps that's a good way of thinking about it. So short term, loss of sleep leads to sort of fluctuations in mood. And what's called a negative salience, I think this is so fascinating, wonderful experiments have shown that the tired brain remembers negative experiences, but forgets the positive ones. So your whole decision making machinery is going to be biased towards the negative rather than the positive. You show increased irritability and anxiety. You have a loss of empathy. So you fail to pick up the social signals from friends, colleagues, potential clients, and you show high levels of frustration and you exhibit that frustration, which of course is not good within the business sector.

4:02Very importantly, you tend to indulge in more risk-taking and impulsivity. One level it's, oh, I think I can make that red traffic light, whereas in fact, you would never do it if you weren't tired. But of course, in the business sector, it means that you may expose yourself to situations because you've done stupid and unreflective things. You tend to use stimulants and then sedatives. So you can drive the waking day overriding the effects of tiredness by endless cups of caffeinated drinks. You get to the evening and think, oh God, I ought to get some sleep at this point. And then you'll try and use a sedative.

4:38and that may be alcohol. And so many people fall into this stimulant-driven and sedative, alcohol-driven sort of sleep-wake cycle. And the key thing about sedatives, like alcohol, like sleeping tablets, is that they're sedatives. They do not provide a biological mimic for sleep. So some of the important stuff going on, memory formation, our ability to come with novel solutions to complex problems are actually impeded by taking sedatives. You can also find with more than just a few days, you start to build up some problems. And that can, of course, build up over weeks and months. So you can have daytime sleepiness, and that's not great.

5:21Microsleeps, I think, is really important because there's uncontrollable falling asleep. Now, if you're driving, that can be literally fatal. 100 ,000 to 300 ,000 crashes on the American freeway have been linked to people just simply falling asleep at the wheel. Then with months of sleep deprivation, then you begin to be more vulnerable to cardiovascular disease, altered stress responses, altered immune responses. And of course, metabolic abnormalities, I think, are so well described. So the slide into type 2 diabetes, the distortion of the metabolic axis, if you're tired, you're throwing the hunger hormone into the circulation.

6:03And so you're eating more sugars and carbohydrates. One study looked at healthy young males with only four hours of sleep versus others who were allowed to sleep up to 10 hours. And after just one week, the hunger hormone ghrelin had gone up by, I think, something like 97%. The satiation hormone leptin had gone down by something like 14%. But carbohydrate consumption just after a week had gone up by 35 to 40%. So not getting the sleep that you need can distort the whole metabolic axis. So it's a vicious circle and you're doing more and more and more and more damage and it's cumulative. Yeah. And if you're vulnerable, then the slide into depression and psychosis can occur.

6:48Some work that we've done here in Oxford has shown that the clear links between sleep-wake disruption, sleep and circadian rhythm disruption, something I might use the shorthand scarred. I know it sounds like Bond villain. And if you have scarred, then the severity of your mental, we studied paranoia and illicitory experiences had gone up. So I think the key point would be that if you don't get sleep, there are the short-term sort of consequences in our cognitive and our emotional responses, longer term, you're really opening up some potential health issues. And I think it illustrates the fact that not getting the sleep that you need, and we should talk about that, is so much more than feeling tired at an inconvenient time.

7:30It has a big effect upon our global health and our ability to function. So really, it's mandatory in anybody's life. But when you're starting a business, you will be a better business person if you look after your sleep. I think that's right. Now, clearly, short term, the need to get that paper written or that report done, sure, we all distort the system, but it's where it's sustained that's so problematic. And I think one needs to be aware that, okay, right, I've done that sort of near all nighter because I had to get that project done. That was the deadline. The next day, I'm going to be really careful about my interactions, what I'm going to take on, and I'm going to try and actually step back.

8:12So it's all about checks and balances. And given we're all different, you say how much sleep you need, how does one find out their personal sleep allowance? I think this is so important, really a fundamentally important point. And it's part of the reason I wrote the book, because I was absolutely fed up with the sort of sergeant majors of sleep screaming, you must get eight hours. And it was terrifying people. I had one chap who came up to me and said, I don't get eight hours of sleep. Am I going to die? And I said, well, we all are. Yeah, I can guarantee you're going to die, but it may not be linked to that.

8:48And so people have become very, very anxious about it. Doesn't help you get a good night's sleep. It really doesn't. In fact, most people don't have a sleep problem. They actually have an anxiety and a stress problem, which prevents them getting the sleep they need. So how much sleep do you need? Well, it's not rocket science. If you're feeling as though you're able to function and you're working optimally during the day, you probably have the sleep that you need. But if you're dependent upon an alarm clock or somebody else to get you out of bed in the morning, that probably means you're not getting enough sleep.

9:20If you oversleep extensively on free days, and particularly when you go away on holiday, and in fact, even though you are setting up a new business, it is important to step back and go away on holiday. But you can see that your sleep will expand hugely. And people often use the weekend, for example, for catch-up sleep. It's not a good strategy. It can partially help, but it can actually distort your sleep-wake cycle. It means that the Monday is actually sort of disrupted. We talk about circadian rhythms, and I was reading that it's about a day, dia being day and saika being about. Should we be in sync with our environment?

9:57So if the sun's coming up and we're waking up naturally with the sun and the sun's going down and we're going to bed naturally with the sun going down. Is that a good rule of thumb? So we have this internal clock, these circadian rhythms, and they run in humans on average. About 90 % of us are a little bit longer than 24 hours. So if we went to a deep dark cave, no light and constant temperature, we get up with respect to the outside a bit later and later and later each day. And what that means is the internal clock needs to be aligned to the external world. And for most of us, the exposure to the light-dark cycle is so critically important.

10:35But light has different effects at different times. So morning light advances the clock, makes us get up a bit earlier and go to bed a bit earlier, whereas dusk light means we'll go to bed a bit later and get up a bit later. And so if you have a clock which is drifting later and later and later, it needs a daily advance. That's why morning light is so important because it's the morning light that advances the clock and the evening light that delays the clock. So just to recap, you should really, as an individual, keep an eye on your sleep patterns. And I know in your book, you have an amazing appendix that will do a survey as to find out who you are and how you operate.

11:15And then really sort of, I guess, agreed with yourself that I am a nine hour person and it's mandatory, I will operate better and more efficiently and my business will be stronger for it if I do that throughout the week and not stockpile at the weekends. Yeah, absolutely. And of course, by trying to override this sort of really fundamental deep biology, we set up all of our health problems. Amazing. And talk a little bit more about naps because you mentioned that they are a thing or should not be a thing. Maybe I'm not sure. I have mixed views about naps. So first of all, if you need a nap, it means that you probably didn't get all the sleep that you needed the night before.

11:53But the occasional nap I don't think is a problem. The data suggests that a short nap of 20 minutes is good and it can improve midday, for example, improve your cognitive abilities and your efficiency later in the day. If you sleep for longer than 20 minutes, you might go into a deeper state of sleep and recovery from that can leave you sort of a bit sort of muggy. So if you're going to have a nap, then, you know, set an alarm for 20 minutes or so. Where it becomes problematic is that if you get very short nighttime sleep, you then get up or you're driven out of bed and then you struggle and then you fall asleep later in the day.

12:37And that's fairly close to bedtime, which then pushes back the pressure for sleep, which means you're not having a nap, you're having a one or two hour sleep, which means you're delaying sleep that night, which means that the opportunity for sleep is diminished, which means you're going to feel tired the next day, and you might fall into the trap of longer naps and shorter nighttime sleep. And that should be avoided. Now, one of the things that's turned out to be very interesting is that the default pattern of human sleep is not a single eight hour or nine hour or six hour block. But it can be called polyphasic, which means or biphasic, which is you fall asleep, you then wake up, sometimes you're aware you've woken up, sometimes you won't be you fall back to sleep again.

13:24And you can have several episodes of waking and falling back to sleep across the night. Now, the problem that many of us have is that if you're anxious or stressed, and if you're setting up a new business, this is sort of embedded in your what you know, your thoughts. Then you wake up and you think, oh, what all the stuff and you can't then fall back to sleep. And I think it's very important that people know that it's fine. If you wake up, you just need not be the end of sleep. Stay calm. You may want to leave the sleeping space, leave the bed, keep the lights low, maybe read a favorite novel.

14:01I remember saying to somebody, you know, well, a few pages of Jane Austen or something. And they came back to me at the end of the talk and they said, does it have to be Jane Austen? I said, no, no, no, just something that you find relaxing. And then you will feel tired to get in and go back to sleep. So not a screen, not a phone. Don't read on a phone. Well, the data there are mixed. You'll read sort of in the media, there's some banner headlines that looking at a Kindle before you go to sleep, for example, will shift your biological clock. Well, they don't have blue lights, do they? Blue light is, there's almost no data at all saying blue lights are having an impact upon sleep versus, it's all about the light intensity that's the most important.

14:44Because what the receptors do, they have a bell-shaped response. So it's not that they won't absorb other colors, other wavelengths. It's just that they're less likely to do it. They're maximally sensitive, these receptors that regulate our sleep-week cycle and our circadian rhythms. in the blue part of the spectrum. These are the receptors we discovered. But they also will absorb other wavelengths as well. And if it's bright enough, it really doesn't matter what. So, you know, these screens that shift from blue light to red light, the evidence that they actually have any impact is almost non-existent.

15:19So just if you're waking up and read something with a dull light. Yeah, exactly. And so the Kindle study, which I think is so interesting, they got people to look at a Kindle on its brightest intensity for four hours before sleep over five days. And at the end of that period, it delayed sleep onset just statistically significantly by 10 minutes. And as one of my colleagues said, well, it might be statistically significant, but that's biologically meaningless. Waking up in the middle of the night, you're like, no, I need my sleep. I've got to get up early because I've got a big day ahead. try not to panic read something that will send you back to sleep and are there any other techniques that you advise oh yes most people will have some sort of an alarm clock by the bed if it's an illuminated one what's the first thing you do you look to the side you think oh my goodness i've only got two hours before the alarm clock goes off and then you say oh my god just start drinking coffee you know doing emails and of course it doesn't matter that you've only got two hours Actually, you know, people get huge advantages of a 20-minute nap.

16:23So why are we dismissing that two hours of additional sleep that you could have before the alarm clock goes off? So what I suggest is actually just cover the face. Don't look at the time. Don't look at the time. It's when the alarm clock goes off that's important, not how long before it goes off. So you can get completely stressed out by it. I always try and set an alarm. I have to fess up to that. But to get to the gym, to be in a bit more of a structured day and try and have as many days I get up at the same time. every day. I try. If I have a late night for work or I wake up in the middle of the night, should I then let myself sleep in or should I stick to my schedule and then try and get back on?

16:59Try and stick to your schedule. Yeah, try and get stick to your schedule, particularly if it's things like the gym. And try not to exercise too late in the day though, because part of sleep initiation is a small drop in core body temperature. And if you block that drop in core body temperature, it could be more difficult to get off to sleep. And so if you're exercising very vigorously prior to bed, that can actually delay sleep onset. And also you're going to be, you know, releasing all of those neurochemicals, which have an alerting effect upon the brain. So evening is fine, but just not too close to bedtime.

17:34And diet, does that have an effect on sleep? Yeah, it's really fascinating. And some new data coming out on this. So in 1100, the main meal of the day was breakfast. That's when the big meal. But by we get to Tudor times, it's the main meal of the day has moved a bit later. So it's about noon. But with advanced industrialization, where people were commuting from their home to the workplace, and then back again, it meant that they didn't have much time in the morning for a decent breakfast. And they probably were pressurized at work. So they didn't have time for a decent lunch, particularly in the last few decades, where the big lunches sort of evaporated.

18:16And then you'd finally get home, and you'd stuff something in the microwave, which would be your main meal of the day. Now, what's been shown is that the circadian system really regulates our metabolism. And the same meal at breakfast time, lunchtime in the evening, the levels of blood glucose, which of course, can be a predisposer to metabolic abnormalities, metabolic syndrome, type 2 diabetes, and indeed obesity, is cleared effectively in the morning at lunchtime, but not cleared later in the day. And if you think about it, our metabolism is profoundly different. We're taking in calories during the day, and we're burning those up to be alive.

19:01And then, of course, at At nighttime, we're not taking in calories, we're mobilizing the calories that we've stored. And so our metabolism is completely different. And so the closer we eat to bedtime, the more likely we're going to take those calories and store them and not burn them up. So you're more prone to, as I say, metabolic syndrome, type 2 diabetes and obesity. And, of course, all of the health consequences of that. so if you can we should be defaulting back to a more sort of breakfast lunchtime main meal of the day really a light a light supper i notice if i go to bed earlier and get up earlier so it could be in bed by half past 10 and up at 5 30 i'm a very much improved human being my team notices it i notice it i get a lot out of my day i feel more efficient even if i get the same amount of sleep if I go to bed at midnight and get up later.

19:56Why is there a difference there? Oh, it's because of our fundamental biology. It's basically the way our clock works, the way we respond to sleep pressure. There are two factors regulating our sleep. One is the clock, which basically says, now is the time to be awake, now is the time to be asleep. But then from the moment we wake in the morning, chemicals build up in the brain, substances like adenosine build up in the brain, and they provide what's called sleep pressure. So what happens is that the sleep pressure builds up and up and up and up and up during the day. You don't fall asleep, ideally, because the clock is saying, stay awake, stay awake, stay awake.

20:32And the clock's drive for wakefulness, ironically, is at its highest just before we fall asleep. Because you've got the sleep pressure, which is really high. The clock is saying, stay awake, stay awake. And it says, okay, now it's time for sleep. The clock kicks in for going to sleep. The sleep pressure is really high and then you fall asleep. So you've got these two systems interacting and they're very variable between individuals. We've talked about your chronotype. I'm guessing that you are probably more of a lark than an owl and therefore going to bed early and getting up early works for you and you should protect that.

21:08Yeah, protecting it. That's the key. And what we're doing with this season about health and wellness with all founders and experts, the previous guest has a question for the next guest. And so the previous question was, what was your biggest leadership challenge? I remember one case where we had a PhD student and this individual just wasn't up to it. And of course, what we do is, I think as mentors, you know, you want to get the best out of people, you want to support them. And it was quite clear that this person was not going to get their PhD. and I remember having to sit them down and say, look, this is not for you.

21:49And I just don't think it's going to work out. And I felt terrible. And I liked them. We got on, but they just weren't going to hack it. But do you know what? They said to me, thank you so much because I know I'm not going to do it. This is not what I want to do. And now I can go on and do the thing that I will be better at. And so I think it was one of the most difficult things I had to do. And I've had another situation like that. But actually, I do think you need to confront it because if it means then you liberate that person to do something that they're really good at. And of course, again, how many times have we said this?

22:25One size does not fit all. And not everybody's up to doing a PhD. They will be brilliant at something else. And that's what they need to go off and find. Amazing. And is there a question you'd like to ask for the next guest who would have also been a founder at some point? Yes, I suppose if you have a partner and a family, how do you balance the demands of a new business and the immense emotional input that you have to put into that with maintaining the relationship and your contact with potentially your children? And I've been in that space and I know that it's really tricky and I would be fascinated to hear how other people deal with that.

23:13Every guest that we've interviewed so far this season has said, yes, mobility is important, but sleep is more important. And yes, nutrition is important, but sleep is the most important. So thank you. I mean, this will be very, very welcomed by many people. Thank you for your time. It's been great to chat. Delighted to chat. It's been great fun. Thank you. Thank you for listening to our 12 Days of Christmas from How to Start Up. If you have enjoyed this episode, please rate and review the show because it honestly makes a massive difference to the podcast being found by other people. And to me as your host, it's nice to know you're there.

23:43Our normal scheduling will resume in January 2026 and we wish you a very, very merry festive season and hope you get some rest.