How well we sleep — and when — is very much determined by our body clock. And the body clock, as I explained in yesterday’s Mail, is regulated by sunrise and sunset: our exposure to light and darkness ‘tells’ the clock in the brain when it is the best time for sleep and wake.Problems with sleep, such as insomnia, are often down to problems with the body clock — typically as a result of the wrong light exposure linked to our 24/7 culture where we try to squeeze more into our days and nights.
But the body clock is not the only driver of sleep. The second key driver is called ‘sleep pressure’. This builds from the moment we wake and rises throughout the day and reaches its highest level in the evening prior to sleep.
We fall asleep naturally when the body clock drive for us to be awake drops, and the sleep pressure is high. Then, as we sleep, sleep pressure declines — and the body clock instructs the brain, and the rest of the body, that it is time to wake up.
THE PERILS OF COFFEE ON THE GO
So what drives sleep pressure? One theory is that it’s down to the build-up of chemicals in the brain. The most likely contender is a molecule called adenosine, which animal studies have shown increases during periods of wakefulness and is then broken down during sleep.
The brain seems to use adenosine levels as a minute-to-minute measure of how long you have been awake. The reason caffeine — in the form of coffee, tea or chocolate — keeps us awake and alert is that it blocks the mechanisms in the brain that detect adenosine.
