Something You Should Know - SYSK TRENDING-How Your Circadian Rhythm Runs Your Life

Episode Date: July 7, 2026

Can you train yourself to become a night owl—or an early bird? Millions of people try. They force themselves to stay up later, wake up earlier, or work overnight because that's what life demands. But can your body really adapt? Or is there a biological clock inside you that simply refuses to cooperate? Scientists now know that your circadian rhythm governs much more than when you feel sleepy. It helps regulate your energy, mood, memory, metabolism, immune system, hormones, and even your risk for a surprising number of chronic diseases. When that internal clock falls out of sync with the schedule you keep, the consequences can range from feeling groggy and unfocused to serious long-term health problems. So how much control do you really have over your body clock? Why do some people naturally spring out of bed at dawn while others come alive after dark? What actually happens when you regularly ignore your body's signals? And what are the simple changes that can help you work with your circadian rhythm instead of constantly fighting it? Russell Foster joins me to explain the remarkable science of the body's internal clock and why understanding it may be one of the most important—and overlooked—keys to better sleep, better health, and better performance. Russell is Professor of Circadian Neuroscience and Director of the Sleep and Circadian Neuroscience Institute at the University of Oxford. He is author of Life Time: Your Body Clock and Its Essential Roles in Good Health and Sleep (https://amzn.to/3QQGZ6v). Whether you think of yourself as an early bird, a night owl, or somewhere in between, this conversation may completely change the way you think about sleep—and about time itself. PLEASE SUPPORT OUR SPONSORS WAYFAIR: Ready to upgrade your home for way less? Head to ⁠https://Wayfair.com⁠ right now to shop all things home and get your space ready for less.  RULA: Thousands of people are already using Rula to get affordable, high-quality therapy that’s actually covered by insurance. Visit ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠https://Rula.com/sysk⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ to get started. QUINCE: Elevate your summer wardrobe. Go to ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠https://Quince.com/sysk⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ for free shipping on your order and 365-day returns. Now available in Canada, too! SHOPIFY: It's time to turn those "what ifs" into CHA CHING with Shopify Today! Sign up for your $1 per month trail and start selling today at ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠https://Shopify.com/sysk⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ Learn more about your ad choices. Visit megaphone.fm/adchoices

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Wayfair, every style, every home. Have you ever wondered why some days you feel sharp and energetic, while other days it's a struggle just to think clearly, even if you got the same amount of sleep? It turns out there's an internal clock, quietly running your life. Your circadian rhythm doesn't just determine when you feel sleepy. It influences your mood, your memory, your metabolism, your immune system, and even when you're most likely to make your best decisions. That's why today's SYSK trending topic is how your

circadian rhythm runs your life. So how does this biological clock actually work and what happens when we ignore it? In my conversation with Russell Foster, one of the world's leading experts on sleep and circadian biology, we're going to explore the fascinating science behind your body's master timekeeper and how to make it work to your advantage right after this. This episode is brought to you by Accenture. When your advertising operations fall out of sync, everything else follows. Spotify and Accenture are working together to reinvent the rhythm of ad sales,

using automation, analytics, and smarter workflows to simplify campaign delivery and access better data across the business. The result? Less time spent on operations, more time connecting brands with the moments and fandoms that matter most. Learn more at Accenture.com slash Spotify. I'm sure you've heard that you have a body clock,

that your body works naturally to get you up in the morning and to go to bed at night. It's your circadian rhythm. It's the way humans are wired. Just as some other creatures are wired to be nocturnal and awake at night, humans are wired to be awake during the day. And that creates problems because a lot of us work nights or we're up late or we're out at night. And all of this impacts your health, physical and mental.

How does that work? Well, meet Russell Foster. He's a professor of circadian neuroscience and director of the Sleep and Circadian Neuroscience Institute at the University of Oxford. He's also author of a book called Lifetime, Your Body Clock and Its Essential Roels in Good Health and Sleep. Hi, Russell, welcome to something you should know. Great to join you, Mike. So let's start by you explaining what this body clock is that we have. You can think of it as sort of an internal biological representation of a day.

And the exciting thing over the past, I suppose, 20, 30 years is we've got a real understanding. of what actually is a biological clock. And a whole bunch of genes are identified, and the fact that they can be turned on, make a bunch of proteins, those proteins can form a complex, and then go into the nucleus of the cell and turn those genes off.

Those proteins are then degraded, and then you have a whole cycle of protein production and degradation. And that's in essence what the clock is, and it's all within a cell. We thought we sort of kind of understood the organization, because there's a structure in the brain called the supra-chaismatic nuclei. And that was identified as, as it were, the master clock in the brain. And we thought that what happened is that this master clock would force 24-hour rhythms or near-24-hour

rhythms in hormone release, in behavior, you name it, on the rest of the body. And then it was discovered that every cell in the body has the capability of generating a circadian rhythm. It has its own clock. And so what you've got is this incredible sort of network of time, coordinated by a master clock in the brain. But actually at the delivery end, in the organs of the liver, the muscles, the gut, they're actually driving the physiological and behavioral changes. So we have, in fact, a circadian system, a circadian network in time. And so what's the purpose of it? It's a really important question. And basically, why we have a clock is that we sit on a planet that revolves once every 24 hours. And this produces profound differences in our environment. So we, of course,

you have a light, dark cycle, we have temperature, we have, you know, cold, we have availability of food and all the rest of it. And these are profound changes. And what the clock can do is allow us to anticipate this predictable change, 24-hour change in the environment, and fine-tune our biology in advance of the change conditions. So before we actually wake up, body temperature is rising, metabolic rate is rising, oxygen efficiency is all rising so that we can deal with the demands of being active. And then at the other end of the day, as we settle down towards sleep, lots of important things are going on whilst we sleep, but we're not active.

And therefore, our oxygen usage goes down, our activity levels go down. These are decreasing in anticipation of sleep. So what you've got a clock for is to anticipate these really profound and predictable changes in the environment. There's also another explanation, which is in addition to aligning our biology to the external world, what a clock can do is also align our internal biology so that the muscles, the nervous system, the gut, are all working at the correct. time relative to each other. And that's another, often forgotten, really important role of our circadian system. So does everybody's clock start out the same, more or less, and then maybe it adapts, or we adapt to it, perhaps, and some people maybe are more morning people, or some people are

late night people, or is the clock set and the clock is set? So we have sort of a bunch of genes, which of course we inherit from our parents. And subtle changes in those genes can tend to make us a morning person or an evening person or somewhere in between. So there's a genetic element to whether we want to get up early or get up late. There's a second element, which is as we age, the hormonal changes associated with puberty also seem to interact with the circadian system. So from the age of 10, we tend to want to get up later.

and later and later and later. And this peaks in our late teens, early 20s. And women tend to peak a little bit earlier than men, and men are peaking later, and they tend to, on average, have longer body clocks. They like to go to bed later and get up later. But after the late teens, early 20s, we move slowly to a more morning chronotype, morningness versus eveningness. So by the time we're in our late 50s, early 60s, we're getting up and going to bed at about the time. We got up and went to bed when we were 10, 11 years of age. There's also a third really important influence on our sleep wake, our circadian timing. And that's when we see light.

So dusk light delays the clock, whereas morning light advances the clock, makes us get up earlier and go to bed earlier. And so when we're all agricultural workers, we got symmetrical exposure to more. morning light and dust light. So we stayed on cue. We did a study a few years ago on university students showing that those who wanted to go to bed the latest, the more owl-like chronotypes, were the ones that were missing out on the morning light, which would advance the clock, make them get up earlier, and got lots of evening, late evening and late afternoon light, which would want to make those individuals get up later. So you've got three things interacting.

You've got your genetics, you've got how old you are, and you've got whether you see light at dawn and dusk. And then I guess you can add into that all the other things from social media, whether you're staying up half the night, you know, looking at your smartphone or doing gaming, which will, in a sense, override those biological drivers of when we want to go to sleep. So when you are staying up all night, Maybe you're a shift worker and you work the graveyard shift.

Are you fighting your clock or does your clock adapt to that shift? No, that's a really important point, Mike. And the assumption was that if you're working on the night shift, you adapt to the demands of working at night. And studies have shown that 97% of night shift workers, long-term night shift workers, have never adapted to the demands of working at night. And so what's happening is your entire biology is saying, you should be asleep when you're forcing yourself to work. And that leads to a bunch of problems. One of the ways we can stay awake whilst, you know, trying to work at night and override this

endogenous biology is by activating the stress system. And long-term activation of the stress system is associated with a whole bunch of problems such as infection and load immunity, the hormone cortisol, the stress hormone cortisol. We know that that suppresses, the immune system and that predisposes individuals to infection and indeed higher rates of cancer. What's so interesting is that the World Health Organization has, you know, on the basis of the data, has said that night shift work is a probable carcinogen because all the studies showing increased cancer rates in night shift workers. You also get increased metabolic abnormalities such as obesity, type 2 diabetes. And indeed,

mental health issues such as depression and psychosis. So long-term disruption of our, you know, trying to work while our bodies are trying to make us go to sleep can lead to some serious health issues. That's the long-term stuff. Short-term we see and the sorts of things that we've all experienced because we've done a few all-nighters, for example, would be fluctuations in mood. The tired brain, interestingly, forgets its positive experiences. but remembers its negative ones. And so our entire worldview, if you're tired, is biased towards negative. And that's the basis of what we're making our decisions.

Irritability, anxiety, risk-taking and impulsivity. We do stupid and unreflective things. We tend to show lower levels of empathy. You know, we don't pick up the social signals from friends, family, and indeed work colleagues. And that can lead, of course, to problems. Poor memory, impaired decision-making, poor communication skills, and a general reduced social connectivity. And those sorts of problems can kick in after relatively short periods of time, you know, a few days. A few days.

Yeah, oh, yes. I mean, you get noticeable differences in what your memory, ability to consolidate memory, after just one day. It's quite remarkable. We're talking about Your Body Clock, what it does how it works, and we're talking with Russell Foster. He is author of the book, Your Body Clock, and its essential role in good health and sleep. In Toronto, every arrival is a statement,

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and I've heard the stories about how working nights or working overnights can cause certain health problems. And I've always thought that part of the problem is that when you work nights and you try to sleep during the day, it's hard to sleep during the day because the doorbell rings, the phone rings, the lawnmowers are going. There's a lot of, there's a lot of disturbances that make, make it difficult to sleep during the day. So that messes up your sleep, which messes up your health.

Yeah, you're right. There are additional disturbances. So when you finish the night shift, you're overwhelmingly tired. And so you've built up a huge sleep pressure. The problem is the body clock has not shifted to the demands of working at night. night. It thinks it's daytime. So whilst this massive sleep pressure is inducing some sleep, the clock is saying, hang on, it's daytime. You should be up. So the quality and the depth of the sleep that you get whilst trying to sleep during the day is never as good. And of course,

you're much more vulnerable to being disturbed because of noises or light coming in through the windows or indeed, you know, cars outside. So yeah, it's a real problem. And I guess we have to answer the question. Well, why don't night shifters adapt? You know, if you're flying across multiple time zones, you will adapt to the multiple, you know, to the new time zone. And again, we have to come back to light. And what's happening is that in the workplace, whether it be the factory or the office at night, you're working under relatively dim artificial light. And then on the journey home, you're experiencing bright natural light or later in the day or indeed on the journey back into work. And what happens is that the clock always defers to the brighter light signal as being daytime

and therefore can never shift the clock. There are a few examples where the clock has been shifted. There's some experiments were done which exposed night shift workers to bright light in the workplace, you know, 2,000 Lux or so, and Lux is a measure of brightness, and then hid them from natural light during the day. And just like getting over jet lag, they adapted to the demands of working at night, because they'd been shifted by the light dark cycle. The problem is that's just not a practical solution for most people. Well, it's always interested me and kind of gives credence to what you're saying is when people work days and they're done with work, they typically

don't come home and go right to bed. But when people work nights, they come home and they go right to bed because they've been fighting this all night long and finally they get home and they just crash. Yeah, absolutely. And the sleep pressure is absolutely overwhelming. But the trouble is it can't fully kick in because the clock is saying, no, it's daytime. You should be awake. This idea, this theory that the light determines when we should get up and when we go to bed or should go to bed, then shouldn't we change the time we get up and go to bed based on the seasons because, you know, the day is longer in the summer, shorter in the winter. So shouldn't that alter our bedtime and wake up time? Yes. In fact, there are very clear evidence showing that as the

seasons expand and contract, the length of sleep would change. Now, today we're somewhat buffered from the seasonal changes because of course we have indoor light. But in the pre-industrial era, I mean, during the winter times, the period of sleep extended and then it contracted during the summer. So yes, we do adapt to the changing day length over the seasons. And we see differences in how long we sleep. But many of us cannot. We have to get up at the same time and go to bed at the same, roughly the same time. There's no adapting going on. We have our schedule in the season doesn't make any difference. That's right. And we're so detached from most seasonal variables anyway. So, yeah, we just have to suck it up and get on with it. What's quite interesting is that some beautiful

studies by Roger Eekirk has shown that historically the sleep at night wasn't a single consolidated episode of, as we're often told, it should be eight hours. There's lots of discussion of, I had a wonderful first sleep, or I had a lovely second sleep. And sleep seemed to have occurred in a series of episodes. And this is called bifasic sleep, waking up once or twice at night, or polyphasic sleep, which is waking up and then going back to sleep again several times during the night. And most of us are unaware that this seems to be the default and natural state of human sleep, as in all mammals. And so one of the great problems is that people will wake up in the middle of the night, think, oh my goodness, you know, I'm never going to get back to sleep,

start to be anxious, and then, you know, just get up, start doing emails, drinking coffee. Whereas if they would stay calm, maybe stay in bed, but if they're not immediately falling back to sleep, then move to a quiet place where the lights are dim, do something relaxing, they're feel tired again, and then return to sleep. And, you know, one of the points of writing lifetime was really to try and get bust some of those myths that you must have eight hours of uninterrupted sleep. That's not true. So sleep can be, you can wake up and go back to sleep many times across the night. And of course, sleep duration, the length of time we sleep varies enormously between individuals and as we age. The healthy range, as defined by the National Sleep Foundation,

it can be from six hours to 10 or 11 hours, depending upon how old you are. So, you know, sleep is like shoe size. One size does not fit all. And the key thing is to try and work out what works best for our particular needs and demands at our particular stage of life. Well, we've been talking as if this is like two things. It's daytime, in nighttime, but what about people, like my wife does this, she has to work really early, so she gets up at four. It's pitch black. Does she then suffer some of what you're talking about? Because she's not getting up with the light. And a lot of people, you know, work really early. Farmers, certain shift workers, get up way before the sun comes up. That's right. And that is a

problem. I don't know how your wife copes with it, but if you're not getting that morning light and and you're commuting off to work and then you're sitting in an office building or inside for the rest of the day, you're not getting that morning light exposure, which is so important to set the body clock. And what might happen is that individuals who are missing morning light might then finally get home whilst it's light and get that evening light. And of course, the evening light will shift their clock to a later time, making it even more difficult for them to get up early in the morning. And so what I think many of us would advise is that, you know, once you've got up, if you've got to get up at 4 o'clock in the morning, then have your breakfast in front of a light box or some other bright light source to try and balance your light exposure to get that morning light. In the Scandinavian countries, for example, you know, it's even worse where for two months of the year in Tromso, for example, it's complete darkness. And many of the families there, they actually have a light box room.

So the whole family, when they've got up, goes into this room, sits in front of a light box, and they get artificial morning light, which sets the clock and helps them function to adapt to the varied demands of rest and activity. And, of course, importantly, keep those varied 24-hour clocks in the organ systems of the body appropriately aligned. So you had talked about earlier about working nights short-term versus long-term. Where's the line between short term and long term? Yeah, I think that's a really good question. We don't precisely know. I mean, we do know that after 20 years, you're really sort of likely to have high risks of cancer,

metabolic abnormalities type two. But some people will be more vulnerable than others, and it may kick in much, much earlier. You can certainly get those signs, certainly for metabolic abnormalities after a relatively short period of of time, just a few years. There was a study, though, that published a few years ago, which showed that long-term shift workers can reduce the risks of cancer and diabetes too if they maintain a rigorously healthy lifestyle. So they're eating really healthy food, so low fat, low sugar, and they're doing lots and lots of exercise. The study was really fascinating because, you know, looked at people over time and you know really high rates of diabetes too with a with a poor

lifestyle but with a healthy lifestyle you know 20 years of night shift work was still a significant problem but it was much lower than those who didn't lead a healthy lifestyle so it's not as though we can't do something about it we can when we talk about night shift I mean I tend to think of overnights but what about people that work like four to midnight does this same apply It'll depend. It's a good point. It depends on their chronotype. So if you're a late person, then working from 4 o'clock in the afternoon until midnight won't be a problem. Whereas, of course, if you're a morning person, that will be bad. And I think one other thing that employers could do is to chronotype the workers. So, for example, it's easy to do. And you could work out whether you're a morning or evening person. And the thing you want to avoid, of course, is putting a morning person. person on a 4 p.m. to midnight shift, that's where the late types would probably do okay. And you wouldn't get some of the severe problems accumulating. And in the same way, if you're a morning type, then having a shift from 4 a.m. to later in the

day wouldn't be so bad for you. But for a night person like myself, that would be a real problem. Well, I think most people know that there is this circadian rhythm, this body clock. but I don't think people have any idea how, well, they do now from listening to you, but people don't have an idea of how important it is and how much control it has over your life and your health. So I think it's really interesting and important to understand it. Russell Foster has been my guest.

He's a professor of circadian neuroscience, director of the Sleep and Circadian Neuroscience Institute at the University of Oxford. And the name of his book is Lifetime, Your Body Clock, and its essential role in good health and sleep. And there's a link to that book in the show notes. It was good to have you here, Russell. It's been really great, Mike. I've really enjoyed talking to you.

And that's it for this week's SYSK trending episode, Sweet Dreams. I'm Mikeer Rothers. Thanks for listening today to Something You Should Know.