Page last updated at 14:19 GMT, Wednesday, 13 February 2008

The science of sleep

By Clare Murphy
Health reporter, BBC News

Sleeping woman
The position you go to sleep in may also have health implications

Shakespeare waxed lyrical about it, and not getting enough of it remains a favourite national gripe.

But it is only relatively recently we have started to understand how sleep impacts upon our health, from where we do it to how we do it.

Latest research suggests that those who live under a flight path - or indeed share their bed with a heavy snorer - may suffer from raised blood pressure as a result.

It seems surprising that even when sleeping, our bodies can display such an adverse reaction to noise.

Yet sleep, we have increasingly come to realise, doesn't mean we turn off for the night when we turn off the light.

Parts of our brain remain incredibly active - and indeed alert to potential dangers in the world outside. They regulate our body accordingly, and if necessary tell us to wake up.

If that sounds bad, pity the dolphin, which always keeps half of its brain awake when asleep so it can continue to swim, come up for air, and of course, avoid predators.

Why do it

For a long time, the function of sleep seemed quite straight forward. It gave our bodies a chance to rest, and indeed conserve energy.

In fact, the amount of energy we save asleep is very small. At an average of 115 calories, it is the equivalent of a piece of toast with a smear of butter, or perhaps that milky bed time drink.

We spend a third of our lives on it
UK average is 7.75 hours per night
Napoleon and Margaret Thatcher averaged four hours a night
We conserve around 115 calories while we sleep

The growing body of research has illustrated that sleep is primarily about the brain, rather than the body.

Parts of it shut down almost completely, like those at the front which control rational thought, for instance, or our ability to make moral choice.

But other sections, notably those in the lower sections of the organ, remain very active.

Sleep may give this area a chance to exercise nerve cell connections that might otherwise deteriorate from lack of activity.

Crucially, it may give us a chance to order our memories, to consolidate the experiences of the day and clear the decks, as it were, for what is to come when we wake.

Not sleeping, so snacking?

But the body is not excluded from the benefits of sleep, and there is increasing evidence to suggest that our physical health is dependent on our brain getting a good night's sleep.

There is no optimum number of hours, it's whatever you need to be alert the next day
Chris Idzikowski
Edinburgh Sleep Centre.

The part of the brain which regulates our food intake, it seems, can only work effectively after proper sleep.

Several studies have now linked poor sleep to obesity - a connection which cannot simply be explained by the fact that if you are not sleeping, you may well be snacking in front of the television.

Shift workers, whose circadian rhythms - the main biological force behind our desire to sleep - may be disrupted by changing work and sleep times, appear more at risk of cardiovascular and gastrointestinal problems.

But while too little sleep may pose a problem, too much may also be undesirable.

There are studies which have shown that those who sleep longer than eight hours a night die younger than those who sleep less.

"It's not really clear why, but we know mortality increases between 4am and 9am in the deepest stage of sleep, so it could be that those who are already that much more vulnerable, are more likely to die if they are still asleep at these times," says Dr Chris Idzikowski, director of the Edinburgh Sleep Centre.

"In any event there is no optimum number of hours, it's whatever you need to be alert the next day."

Snuggling up

And while struggling to find that perfect balance between sleep and being awake, one apparently also needs to attend to the position adopted before nodding off.

The "freefall" position - when you lie on your front with your hands around the pillow and head turned to one side - is said to be the best for those keen to digest their dinner effectively overnight.

The self-explanatory "starfish" and "soldier" - when you lie on your back with both arms pinned to your sides - are believed to be more likely to cause you to snore.

This may not just mean a bad night's sleep for you, it may also, we now know, set your partner's pulse racing too.

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