Reality television took an alarming new turn this week with a gameshow based on depriving people of sleep. Barry Nelson looks at why a good night's sleep is important for everyone.

THE heavily-criticised Channel 4 programme Shattered comes to a climax on Sunday after a week in which young contestants have vied with each other to stay awake. With the lure of a cash prize of £100,000, 12 contestants have been forced to do without sleep while being asked to perform a variety of tasks.

In the same spirit as the American dance marathons of the 1930s - famously captured by the cult Sixties film "They Shoot Horses Don't They? - the last man or woman standing when the gameshow ends this Sunday night scoops the loot. Predictably, the contestants have struggled and in some cases, have even begun to hallucinate.

Chris Wandel, 22, says he has seen objects flying around the set because he is so tired. Another contestant, Burke, 22, has talked of seeing "white flashes" because of lack of sleep.

Medical advisors have been on hand throughout the programme in case of health problems - and in some cases they have insisted that contestants should be allowed short naps - but that has not placated the critics.

Don Foster MP, the Liberal Democrat culture spokesman says: "This is reality TV gone mad, reminiscent of the degrading American dance marathons of the Depression. Pushing your body to breaking point in the hope of winning £100,000 is not courageous, it is dangerous and demeaning."

John Beyer, who runs the media pressure group Mediawatch UK, also attacks the concept of Shattered. "Sleep deprivation is one of the tools used in brainwashing. It concerns me what these contestants have laid themselves open to."

Shattered may be an extreme version of our 24/7 lifestyle, but in modern Britain millions of people don't spend enough time in bed, and suffer for it. A survey of more than 1,000 people, commissioned by Horlicks, revealed that one in five workers admits nodding off while at work - and yet Britons still work the longest hours in Europe.

More seriously, falling asleep at the wheel causes a number of fatal accidents every year, including the appalling tragedy near Selby, when ten rail passengers died after Gary Hart fell asleep at the wheel of his Land Rover.

So if we're forever dreaming of sleep, how much do we really need?

''You need to get what is right for you,'' says Neil Stanley, director of Sleep Research at the University of Surrey. ''Each person is individual. It's whatever you need to feel awake the next day. Anywhere from three to 11 hours is all right.''

Stanley, also the resident sleep scientist on Shattered, says: ''The idea of eight hours is probably an average. If you can get by with less, then fine - I'm about a nine hour man.''

The amount of sleep you need is largely governed by genes he says. If your parents hibernate for 11 hours every night, then it's likely you'll suffer (or rather enjoy) the same fate.

''A lot is to do with genetics. Some people are tall and some short. In the same way some people need longer and some shorter hours asleep.''

But Stanley concedes there are some who simply love their beds too much. ''Over 11 hours is abnormal, some people are just lazy - like some students.''

Professor Jim Horne, Director of the Sleep Research Centre at Loughborough University, believes it's not just a matter of how long you sleep, but also how well. ''It's a matter of quality not quantity. Six hours of quality sleep is better than ten hours, but most people in the UK seem quite satisfied with seven or seven-and-a-half hours. The function of sleep is for the brain. Below the neck, little goes wrong through lack of sleep. But without it you can become a robot.''

Sleep deprivation, a very effective method of torture for centuries, leaves us feeling quite simply more stupid. The thought process is severely impaired, giving some indication as to the dumbing effect. Some doctors even suggest that not getting enough sleep is bad for health, but mood swings and grumpiness are by far the earliest and most obvious symptoms.

''What is affected is reaction and judgment,'' says Stanley. ''Judgment is very important. The major effect is that performance reduces quite rapidly. It then gets progressively worse, like you're drunk - and it's not to be encouraged.''

Lack of sleep will also destroy concentration, and things we take for granted will gradually fail, such as speech. More dangerously, as we push the limits we can suffer from hallucinations. And if lack of concentration doesn't sound serious, Stanley points to the recent tragedy of the Selby train crash.

''As we saw with the Selby rail crash, 24 hours without sleep is dangerous,'' says Stanley. ''We think we can get through it, but we can't.''

Sleep is vital to our development, he says. ''Generally speaking, sleep has a lot to do with growth and regeneration.''

Although that applies more when you're young than old, it is also important for those recovering from surgery, for example. When you're young you have a lot to learn - the brain needs to file it away - therefore children need more sleep.

It is not known exactly how long we can survive without sleep. The longest period on record is 11 days, set in 1964 by Randy Gardner during his clinical trial into the effects of sleep deprivation. No doubt the Shattered stars will be glad to leave their trial after a week of little more than short naps.

Professor Chris Dodds, who runs the sleep investigation unit at James Cook University Hospital in Middlesbrough, says most sleep problems he sees are related to a condition called sleep apnoea, in which heavy snoring disrupts deep sleep.

"People suffering from sleep apnoea often do not realise they have the condition because they are not aware of waking up during the night. A positive diagnosis is usually made because their partner insists they see a doctor," says Prof Dodds. Disruption of deep sleep can have a devastating effect on people.

"You see people losing their jobs because they are seen as lazy and they can't make decisions. They can also be irritable, bad tempered and even aggressive."

In rare cases where a child has sleep apnoea, their growth is often impaired. "When the problem is sorted out they catch up very quickly."

Fortunately, in the great majority of sleep apnoea cases, the problem can be sorted out by providing the patient with a small air pump which prevents their soft palates from collapsing during sleep.

The Shattered test is extreme endurance, but how can we combat lack of sleep in everyday life?

Both Stanley and Horne are fans of 'power naps' - 20-30 minute sleeps, along the lines of 40 winks, rather than hour-long siestas.

''Naps are wonderful things and should be encouraged,'' says Stanley. ''A nap is the answer to tiredness, coffee is not. We're trying to have a 24-hour society, but without the siestas, it won't work."