Monday, 15 July, 2002, 12:54 GMT 13:54 UK - Neil Stanley

Sleep 'key to longer life'

Scientists believe they may have uncovered the reason why women live longer than men - they are better sleepers. A team from the US has found that women tend to sleep more soundly than men. They are also less affected by the effects of sleep deprivation.

It is wrong to perceive sleep as a passive state of unconsciousness

The researchers, from Pennsylvania State University, found that missing sleep can affect hormone levels and generate harmful chemicals in the body.

Lead researcher Dr Alexandros Vgontzas believes women's sleeping habits may have evolved to help them cope with crying babies and disturbed nights. He thought it could help explain why women live, on average, several years longer than men.

The scientists studied the effects of missing two hours' sleep per night on 25 men and women aged in their 20s.

After a week, the volunteers had become drowsier and did not perform as well in vigilance tests.

Both sexes showed increased levels of inflammatory chemicals called cytokines but only men had raised levels of a chemical called tumour necrosis factor alpha (TNF), which may contribute to the development of obesity and diabetes.

Dr Vgontzas said: "Women are sleeping better, so can this be one of the reasons they are living longer? Greater increases in TNF-alpha levels put men at greater health risks from lack of sleep."

The study showed that women had 70 minutes of deep sleep per night compared with 40 minutes for men.

In the UK, the life expectancy of women is 81 years and for men 75.

Dr Vgontzas said it was possible the seven year gap could be closed if men were able to sleep more like women.

Body clock

Neil Stanley, of the Human Psychopharmacology Research Unit at Surrey University, told BBC that it was difficult to draw general conclusions about the effect of sleep because each person varied from the next.

But he said: "We know good sleep is central to good health. It is wrong to perceive sleep as a passive state of unconsciousness, the body is doing an awful lot while we sleep."

Mr Stanley said the human body relied on a regular rhythm. For instance, the production of many hormones was closely related to the 24-hour body clock.

For this reason, shift work and the 24/7 culture was likely to have a negative impact on health because it disrupted natural body rhythms.

"We are going against nature, and if we do that, then we are always likely to have to pay a price."

The research is published in the journal Chemistry and Industry.