A research team from Burgos, Spain, says that people with sleep apnoea - a condition that causes snoring and irregular breathing - are seven times more likely to crash than other drivers.

Previous reports have shown that sufferers are only twice or three times as likely to have road accidents.

The research comes as a UK poll shows that up to 11% of drivers admit to having fallen asleep at the wheel.

Sleep apnoea is caused by the throat temporarily closing during sleep.

The sleeper wakes violently because of a lack of oxygen.

The condition, which is more common in overweight people, can cause extreme fatigue because many hours of sleep are lost.

It can be identified only through monitoring the way people sleep.

Screening

The Spanish researchers studied 102 drivers who had been given emergency treatment for traffic accidents between April and December 1995.

A random group of 152 patients was chosen as a control.

The patients were screened for sleep apnoea at home.

Other factors such as alcohol consumption, age, driving experience and use of drugs which cause drowsiness were taken into account.

The researchers found that 4% of men and 2% of women in their study suffered from sleep apnoea.

Writing in the New England Journal of Medicine, the researchers concluded: "There is a strong association between sleep apnoea...and the risk of traffic accidents."

A 1988 study by the US National Commission on Sleep Disorders found that drowsiness was a factor in about half of all traffic accidents and 36% of fatal accidents.

Tougher action

In an accompanying editorial, Dr Paul Suratt of the University of Virginia Medical Centre and Dr Larry Findley of the Sleep Disorders Center of Northern Colorado call for tougher action on sleep disorders.