Sleep deprived

"I'll sleep when I'm dead," sang Jon Bon Jovi and judging by the number of coffee shops on our high streets, most people feel the same way. We're a caffeine culture, bent on staying awake at all costs.

Sleeping when you're dead is all well and good but avoiding sleep when you're alive is not to be recommended. You won't be in much of a mood for whooping it up. You'll be tired, irritable and forgetful—and that's just from mild sleep deprivation. If you don't get enough sleep for months on end the health consequences are much worse.

Why do we need to sleep at all?

We spend about one-third of our lives asleep. What's the purpose of all that downtime?

"Humans have a great big brain which needs lots of attention," says Dr Russell Foster, director of the Sleep and Circadian Neuroscience Institute (SCNi) at the University of Oxford. "During the day, masses and masses of information is flooding in and that information cannot be processed while we're 'online'."

Professor Foster uses the analogy of a computer that performs a number of housekeeping functions when it's offline. The brain's housekeeping functions may include fixing memories in the brain and regulating the immune system, but no one knows for certain.

A recent study by the University of Rochester in New York found that the brain cells of mice shrink when they're asleep, allowing cerebrospinal fluid to flush out harmful proteins, which are by-products of the brain's activity. A build-up of these proteins is associated with Alzheimer's disease, dementia and other brain disorders.

However, different animals are likely to have evolved sleep for different purposes and scientists don't know if this flushing-out process occurs in humans. Even if it does, it is unlikely to be the sole purpose of sleep; merely another of the brain's many housekeeping functions.