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.
How to Sleep Better
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.
This means the brain cannot detect how tired it is even when adenosine levels are raised.
But while the short-term use of caffeinated drinks can be useful in keeping us awake during long motorway journeys, for instance, you need to be careful, because as the effects of caffeine wear off we can experience a wave of profound and overwhelming tiredness that can cause us to fall asleep at the wheel.
This is why you need a steady infusion of caffeine if you are on a long trip. Either way, the bottom line is, don’t drive if you are tired. The body clock and sleep pressure do not act alone — additional factors, including our genes, our emotional state, and our age (see panel), combine to deliver the sleep and wake pattern that we get.
And any of these can also alter that pattern, leading to sleep problems. Today, I look at some of the most common sleep issues, in particular insomnia, and what you can do to tackle them.
YOU MAY NOT HAVE A PROBLEM
One of the main causes of sleep problems is a ‘faulty’ body clock and, typically, insomnia is the result. ‘Insomnia’ is the term we use medically to describe difficulties falling asleep or staying asleep as long as the individual would like. But what many people might regard as insomnia may, in fact, be a natural way of sleeping.
Some humans and other animals do not sleep in a single consolidated block of sleep — they have two episodes of sleep (known as biphasic sleep) or even multiple episodes (called polyphasic sleep), where the periods of sleep are separated by short periods of being awake.
People who sleep in this pattern are regarded as suffering from ‘insomnia’. Yet it may be that having a single period of sleep without waking (monophasic sleep) is not, in fact, the normal state of human sleep as many assume — it could be as a result of a shortened night and less opportunity to sleep.
Historical records and laboratory studies where individuals have been exposed to 12 hours of light and 12 hours of darkness support the idea that when we have the opportunity to sleep longer, we revert to polyphasic sleep, with several sleep episodes interrupted by short periods of wakefulness.
This raises the important point: if the natural state of human sleep is polyphasic, then we need to re-think our interpretation of disrupted sleep at night.