Clocking your body: Sleep
We all have slightly different “time signatures”: some of us see ourselves as obvious early birds, others as night owls.
You can work out your own chronotype quite easily; you just need to calculate the mid-point of your sleep on a typical night when you can go bed and get up when you want (which is probably more likely to be at a weekend than in the week). The average mid-point is 4.15 am, and for most people it lies within an hour either side. If yours is outside this range, you’re a definite early or late type.
Why does it matter? Because the time at which we sleep is controlled by two clocks. One is our inner, biological clock, and that depends on our chronotype. The other are the clocks imposed by the outside world, such as the alarm clock or evening engagements. Both of these clocks are ticking continuously but they’re often not in synchrony. The result is what Till Roennenberg, a professor at the Munich Institute of Medical Psychology, has dubbed “social jet lag”.
And this has consequences. It often makes it difficult to get a good night’s sleep but, more importantly, it can have serious health effects. People who wake up too early or stay up too late are more likely to smoke, to be depressed and drink and eat more: it causes their metabolism to react in ways that lead to weight gain. Roennenberg says that for every hour of chronic social jet lag, the risk of being overweight or obese rises by about 33%.
About two-thirds of the population are reckoned to suffer from social jet lag. This is what typically happens…
At the weekend, you sleep in and go out late, and then your sleep schedule is closer to your body’s natural rhythm. Come Monday, the alarm-clock goes off and you’re forced into a pattern that’s out of synchrony with your body-clock. It’s just like travel jet lag – like flying Paris-New York on Friday and returning on Monday. Only worse. When travelling, you can re-set your biological clock using the daylight where you arrive (Our last blog demonstrated how to do this). With social jet lag, on the other hand, you stay in the same place but you’re effectively in a different time zone in comparison with your biological clock. In fact, many of us live in a state of chronic tiredness, and this is inevitably damaging for our health, performance and wellbeing.
What can we do about it, short of smashing the alarm-clock? One way is much like coping with travel jet lag: using daylight to help synchronise our internal clocks more closely with our social clocks.
If you feel your biological clock makes you sleepy too early – say, you want to enjoy more of the night – then seek outside light in the afternoon and evening. Even without sports or activity, evening light in particular can nudge your clock onto a later time. Conversely, if you feel your internal clock is not letting you sleep early enough – to get a decent sleep before the alarm goes off, for example – then spend as much time as you can outside in the morning light. Don’t forget that even bright artificial light is much less intense than sunlight outside, so it has to be full daylight.
Here’s a chart summarising what to do if you feel sleepy earlier or later than you’d like to:
|Mid-point of sleep on a ‘’natural” night||Before 3.15 am||3.15 am – 5.15 am||After 5.15 am|
|You are:||An early bird||Normal||A late owl|
|So, you have to:||Get all the
evening light you
|Just enjoy!||Get all the morning
light you can
Don’t forget, putting the clocks back is like inflicting an hour’s social jet lag on ourselves, and vice versa when we put them forward. In order to nudge your body-clock back to synchronise with the new time, you want to be getting as much late-day light as you can. So, walk everywhere you can in the afternoons – to the shops, to the park, to meetings or, of course, to your treatment or workout at Grace Belgravia.