That was the finding of a study presented at a meeting of the American College of Chest Physicians in Chicago.

The study, carried out at the National Naval Medical Centre in Bethesda, Maryland, looked at 29 men and women with sleep apnoea - which causes the airway to become temporarily blocked several times during sleep - who were receiving treatment for the condition.

They were asked to rate their sex lives before and after treatment - and found that afterwards they experienced better orgasms and improved sexual drive.

Hormone effects

Janet Myers, who led the study, said: "In men, sexual dysfunction may be related to suppression of reproductive or hormonal functioning."

She said that men may also have diminished oxygen levels in their bloodstream that could hinder erection.

She treated the volunteers by placing a special mask over their face as they slept. This was attached to an air compressor that forced air through the nasal passages.

Altogether patients were asked about five categories of sexual performance. Apart form the two in which they showed improvement, these were sexual cognition or fantasy, sexual arousal, and sexual behaviour.

"If patients are more alert, they're less fatigued, and they're more likely to have better sexual functioning," Ms Myers said.

Many of those taking part in the study were moderately obese - a recognised risk factor for sleep apnoea - and the mean age was 45.

Common problem

Obstructive sleep apnoea is thought to affect approximately four per cent of women and nine percent of men between the ages of 30 and 60 years.

Studies have shown that people with the condition are so fatigued during the day that when driving, their performance is similar to that of a drunk driver.

Surgery for sleep apnoea is not generally effective, although the use of masks is becoming commonplace in those who need treatment.