Your body is a time machine. As Russell Foster, the professor of circadian neuroscience at the University of Oxford, says: “What our biology has evolved to do is to deliver the right materials, at the right concentration, to the right tissues and organs, at the right time of day. It’s the circadian system that provides this extraordinary time structure for this to all occur.”
Only, in the fast muddle of modern life it can go haywire. “Without this time structure everything begins to fall apart — not just the sleep-wake cycle, but our metabolism, our immune system, our vulnerability to infection. You name it, it begins to collapse,” says Foster, the author of Life Time: The New Science of the Body Clock, and How It Can Revolutionalize Your Sleep and Health. “It really is at the centre of our ability to function. And one key element of the circadian system and our 24-hour world is the sleep-wake rhythm.”
Fortunately for those of us whose body clock is keeping poor time, Foster’s work as director of the Sir Jules Thorn Sleep and Circadian Neuroscience Institute at Oxford has been primarily on how circadian rhythms are regulated. And if our body clock is to anticipate the changes of the day and the night, and co-ordinate and fine-tune our biology accordingly, he says, it needs to be appropriately set. Want to sleep better in 2023? The key is to reset that body clock. Here Foster explains how.
Get 30 minutes of outdoor light before 10 to set you right
Only 10 per cent of us are larks — who naturally feel tired early and rise early — while 25 per cent of us are night owls, which means that we naturally feel tired later and get up later, and 65 per cent are doves — in between. (In addition, our body clock’s day tends to be a little longer than 24 hours, meaning that under constant conditions “you get up a bit later, and later, and later.”) So to align our clock with our work and lifestyle, most of us need to shift our sleep phase forward.
We can do this by stepping outside and treating ourselves to a robust blast of early morning light. (In winter, when that’s tricky, you can use a light box.) “That will advance the clock and make you get up a bit earlier,” he says. Why? Because, as Foster and his team discovered, in addition to the rods and cones, “there’s a third light-sensitive system in the eye that detects the dawn-dusk cycle and sets the internal clock to the external world”.
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Better to get out at 7am or 8am than 10am, he says. “Light during the middle of the day doesn’t have much of an effect.” However, “shortly after dawn, natural light is 50 times brighter than internal light.” Half an hour outside first thing would be ideal. (He suspects dog owners tend to have a better sleep-wake pattern because they are forced out on early walks.)
For those of us cowering indoors, a brightly lit room won’t cut it. Because these new light-sensitive receptors are relatively insensitive to light, he says, “light that we encounter inside will have a very minor effect”. (One theory as to why we’ve evolved to be so insensitive to such light is so our clocks aren’t confused by the brightness of firelight.) Incidentally, a stroll at sunset isn’t wise if we’re hoping to train our body clock to an earlier bedtime. “Late afternoon or early evening light delays the clock and makes us go to bed later and get up later.”
A nap is better than a lie-in
If we do sleep badly, surely a weekend lie-in makes sense? We might feel better that day, but, alas, a lie-in is disruptive to the body clock because we miss that clock-syncing morning light exposure. So if you need to catch up on sleep at the weekend, a nap is the better option (with caveats), Foster says. “As long as the nap is relatively short — the recommended nap duration based on lab studies is about 20 minutes — and not too close to bedtime.” At lunchtime or early afternoon it will give you a boost, he says, and improve the second part of the day.
How much sleep do I need?
Foster wrote Life Time partly because he was “fed up of the sergeant majors of sleep screaming, ‘You must get eight hours of sleep.’” It’s not true, he says, it’s merely an average. The National Sleep Foundation — an American organisation whose advisory board he sits on — recommends between six hours and ten. So to know if you’re getting enough sleep for you, ask, “Are you able to perform at your peak during the day? Are you able to do what you need to do at optimum?” If yes, chances are that you’re sleeping easy.
Signs that you aren’t getting enough shut-eye, however, are if you answer yes to the following: “Do you oversleep extensively at the weekend, or on holidays? Are you dependent on an alarm clock or another person to wake you up in the morning?” If you’re sleep-deprived, you’ll take a long time to wake up and struggle with sleep inertia and grogginess. Short-term sleep loss causes changes in our mood, increased irritability, anxiety and loss of empathy. You’ll feel irritable and fatigued. You’ll crave daytime naps. It’s likely too, he says, that “your behaviour is overly impulsive — you find you’re doing stupid and unreflective things”. You might also crave caffeinated and sugar-rich drinks. (It’s a dangerous spiral, he says, especially if you try to reverse their stimulating effects with alcohol or sleeping tablets.)
Keep your hands and feet warm to help you nod off
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There’s a slight drop in core body temperature before you fall asleep and, according to Foster, “if you block it, it’s more difficult to get to sleep”. So if your bedroom is too hot you’ll struggle. However, if your hands and feet are cold (perhaps if you have Raynaud’s syndrome) you may have trouble dropping off since — counterintuitively — this will prevent the body cooling.
Foster says: “Part of the reason we have that one degree drop in core body temperature is that we’re losing heat through our hands and feet and other large surface areas.” But if those blood vessels are shut down, we can’t move blood to the extremities and it’s much harder to lose heat. He advises: “Get a good pair of socks and some mittens and that will keep your feet and hands warm and should increase blood flow from the core to the periphery, to lose that little bit of heat from the core that you need to get you to sleep.”
Make your bedroom a sleep haven (consider separate duvets)
People with different chronotypes have the longest-surviving relationships, apparently. Cynics might say this is because they barely see each other, Foster acknowledges, but he suspects that being able to accommodate your beloved’s sleep patterns “shows you’ve got the emotional flexibility to deal with all the crap being in a partnership throws at you”. Investing in a decent duvet, pillows and mattress can facilitate mutual toleration. But if you feel your partner moving at night, might separate mattresses and duvets be the answer? “Absolutely.” Furthermore, if your partner snores and you have a spare room, “it’s perfectly acceptable to have separate sleeping spaces”.
Meanwhile, he says, research suggests that “defining” your bedroom/s with a particular scent, such as lavender, can cue you up for restful sleep. “Because you then go into that space and it reinforces that fact: ‘OK, this is the space for sleep, and I associate it with that particular smell.’ ”
Don’t discuss your finances in bed
Step back from stressful or stimulating situations towards the end of the day, Foster says. No discussing your tax bill beneath the sheets. “In our household the topic of family finances or anything like that is completely banned just before we go to bed.” He also advises against watching the (sad) news or The Silence of the Lambs before turning in. I mention feeling sleepy at ten, rousing myself to watch Happy Valley — then being wide-eyed at 2am. “You activate the stress axis, which overrides the biological need to sleep,” he says. “Essentially, you’ve given yourself a big alerting dose. Our alerting systems are really good at keeping us awake if we activate them.”
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He notes too that it’s the brain-alerting content of your handheld screen keeping you awake rather than the light emitted from it. (“Studies exposed individuals to the brightest light setting on a Kindle for four hours on five consecutive nights just before bed.” It delayed sleep onset by a piffling two minutes a day.) It’s best to turn off screens at least 30 minutes before bed. He used to be snooty about mindfulness — he’s now humbled by the data, which shows it can improve sleep enormously. “That winding-down process before sleep is so important — turning everything off, maybe reading your favourite Jane Austen or listening to a relaxing piece of music — getting into the state of sleep.”
Stop obsessing about getting a “block” of sleep
Eight hours of uninterrupted sleep is the dream. In fact it’s normal to wake several times a night. “The natural sleep pattern of humans, like all mammals, is almost certainly biphasic or polyphasic — which means you go to sleep, you wake up, you go to sleep again, you wake up. It’s not a single consolidated block.” If people could understand that “it’s perfectly fine to wake” and relax about it — “keep the lights low, wait until they drift back off” — they would sleep better, he says. But we panic and clock-watch — “‘oh my God, I’ve only got two hours before the alarm goes off’ — that causes anxiety and they don’t fall back asleep.” Foster advises not thinking about your alarm until it goes off.
One man was so freaked out by his sleep app data, he informed Foster that he set his alarm at 3am to check how much slow wave sleep he was getting. No sleep app, to Foster’s knowledge, has been endorsed by a sleep federation. “The evidence base for their use and their accuracy is very thin,” he says. For broad information, sleep and waking times they can be useful, “but further drilling down into slow wave versus REM is deeply unhelpful”. He says: “So many people don’t have a sleep problem, they have an anxiety problem, which prevents them from getting the sleep that they as an individual need.”
Life Time: The New Science of the Body Clock, and How It Can Revolutionize Your Sleep and Health by Russell Foster is published in paperback tomorrow by Penguin, £10.99
