Ask An Expert: Your Sleep Questions Answered by a Circadian Neuroscientist

Do we all need eight hours of sleep?

This is the message we get from the sergeant majors of sleep. It's one of the reasons I wrote Lifetime because it's nonsense. Healthy sleep can range from six hours to ten or more.

It's like shoe size, trying to make everybody wear the same shoe size is like everybody having to have the same sleep pattern. It's very, very different.

Is blue light before bed really a problem?

Well, the sort of light and levels of light you get from computer screens or tablets or phones and things that isn't really bright enough to have much of an effect. So I don't think we should be worrying too much about blue light.

Clearly, if the light is bright, actually whatever colour or wavelength, it can increase alertness and delay sleep. But the sorts of levels you're getting from most devices, there's no real evidence that it will impact upon our sleep or circadian rhythms.

Is it bad to wake up in the night?

It looks like the default pattern for human sleep is very much to wake up and then go back to sleep again. Most of us are unaware that we've woken up. But if you do wake up in the middle of the night, it's nothing to worry about. If you stay relaxed and calm, you will get back to sleep.

What should you do if you can’t get back to sleep?

It's about staying calm. You may want to stay in bed and just relax. Other people are very keen to sort of get out of bed, have a few pages of Jane Austen on their Kindle or whatever, and then as soon as you feel tired, you can go back.

I will listen to some BBC Radio 4 Extra. And I have to say that Melvyn Bragg’s In Our Time does it for me. I love the programmes; it's so relaxing and gentle that it helps me get back to sleep.

Should we eat more, earlier in the day?

So the overwhelming evidence is to concentrate one's calorie intake during the first half of the day – breakfast and lunch – and have a light supper.

Circadian rhythms are sort of geared up to process food during the first part of the day. And so what you see is if you give somebody a constant infusion of glucose, you see that glucose is taken out of circulation quickly during the first half of the day, but before bed it can hang around a long time and of course it's not being used up.

And so it's led to deposits such as glycogen in the liver or fat. So very much concentrate your calorie intake during the first half of the day.

Does alcohol help you sleep?

A drink before you go to bed can be relaxing but if you're using alcohol to get to sleep, you're not getting sleep. You're getting sedation. And it can actually be harmful to some of the important things going on within the brain whilst you sleep, like memory formation and the processing of information to come up with novel solutions to complex ideas. So don't use alcohol as a sedative. It's a really bad idea.

Is it okay to nap?

I think sleep is a very complicated behaviour, so I wouldn't put any strong rules of do and don’t. An occasional nap of less than 20 or 30 minutes is probably fine.

The danger about naps is if they become longer and if they're close to bedtime. If they're longer, you can fall into a deeper sleep. And so recovery from that deeper sleep can leave you groggy. But if you're also close to bedtime, that can be a problem because it pushes back the sleep pressure.

Occasional nap? Fine. If you become dependent on them to get through the day, that's when I start to get a little uneasy.

How do I know if I’m not getting enough sleep?

People around you are often the first to notice. Are they saying you seem to be overly impulsive? You don't seem to be as reflective? You don't seem to have the same sense of humour? You're not as empathetic? That you are showing higher degrees of anger? These are absolutely characteristic of not getting enough sleep.

Also try to notice in yourself if you're doing stupid, impulsive things – things you wouldn't do if you were fully rested. It's about listening to others and also having the courage to listen to yourself.

What’s the best way to relax before bed?

De-stressing comes in a whole variety of different ways. There's some beautiful data showing that mindfulness for some people can be a fantastic relaxation technique.

For others it's going to the gym, not too close to bedtime. It may be listening to a wonderful piece of music. My own sleep patterns improve enormously when The Proms are on.

It may be just winding down and reading a few pages of your favourite novel. It's finding those relaxation techniques that work for you.

What is chronotype and why is it important?

So chronotype is really fascinating. So there genuinely are morning types called larks, intermediate types called doves and night owls. It's about 5% larks, 65% doves, and about 25% owls.

There are three components that add to our chronotype. One is our genetics. The second area would be age. The third area that contributes to our chronotype is when we see light.

How should we use light to improve sleep?

Morning light advances the clock. It makes you get up earlier and go to bed earlier. Evening light delays the clock.

If you're a late type and you need to get up early for your work, then go outside and that morning light will advance the clock. And so it'll be easier to get up in the morning. But you've got to stick to it.

When should we stop drinking caffeine?

Caffeine is really interesting. So what caffeine does is block the receptors in the brain which detect adenosine. Now, adenosine is one of those substances in the brain that builds up the longer we've been awake.

Some people are exquisitely sensitive, and a coffee in the mid-afternoon can delay sleep onset many hours later. Other people can drink several espressos before going to bed and it won't affect them.

Avoiding, by and large, coffee no later than 2 or 3:00 in the afternoon. That's my rule of thumb.

When are we cognitively at our best?

There is a circadian rhythm in our cognitive abilities. Numerical accuracy rises sharply from the point we wake in adults, it peaks at around about noon and then will decline as we go throughout the day.

Peak performance in an adult will be around about noon. The best cognitive enhancer on the planet is a good night of sleep.

Across the mental health spectrum, sleep is now recognised as being critically important.

How important is routine to sleep quality?

The more stable your lifestyle, the more stable the circadian system and the sleep wake cycle. So stability is really important both on workdays and on free days.

What makes a good bedroom?

They should be a place of tranquillity, of calm. And that's where you go to sleep. You make sure that it's not too warm. It's not too hot. You should make sure it's dark. You should make sure that the bedding is good and that it’s this cocoon where you can relax and sleep.

We spend 30% of our lives in bed so why not enjoy it? Why not invest in a pillow that feels wonderful or a duvet that's the right temperature for you and a decent mattress?

How has your own routine changed?

I will now go to bed between 11 and 12. Whereas I think the rule was 2:00 in the morning. And that wasn't great.

As a student, I was working through, sometimes until dawn. And so I was doing all the things as a young person I am now telling people not to do.

I actively avoid any sort of stressful, anxiety-making situations. I think it's called doom scrolling. I don't doom scroll.

Russell Foster is Professor of Circadian Neuroscience at The University of Oxford