People who take short naps during the day cut their risk of dying of heart problems by at least a third, according to a recent study which adds weight to evidence that good sleep is crucial for a long life.

Researchers found that people who had a short sleep at midday - even if it was not regular - had a 34% lower chance of dying from heart disease than those who stayed awake all day. Those who were most serious about their siestas, sleeping at least three times a week and for 30 minutes or more a time, had a 37% lower risk of heart-related death.

"We interpret our findings as indicating that among healthy adults, siesta, possibly on account of stress-releasing consequences, may reduce coronary mortality," wrote the scientists in today's issue of the Archives of Internal Medicine.

"This is an important finding because the siesta habit is common in many parts of the world, including the Mediterranean region and Central America."

The effect was most pronounced among working men - regular midday sleepers in this group had a 64% lower risk of death from heart disease during the study than those who did not nap. In comparison, non-working men who took naps had a 36% reduction in risk.

Androniki Naska of the University of Athens medical school in Greece wrote that the stronger association found in working men could be because they were more likely to face job-related stress than non-working men.

In the project, researchers studied more than 23,000 men and women between the ages of 20 and 86 who did not have a history of heart disease or other severe conditions when they were recruited between 1994 and 1999. Participants were asked if they took midday naps and, if so, how often and for how long at a time.

They also reported their level of physical activity and dietary habits over the previous year.

In the years that the volunteers were followed up, 792 participants died, including 133 who died from heart disease.

Though he found a clear association between siesta and heart disease, Professor Naska's team did not try to explain the mechanism behind his results in his paper. But previous research on animals has shown a link between sleep deprivation and the working of the nervous system.

"There are various lines of work that suggest that if you sleep deprive people, then you get an increase in sympathetic nerve activity, one of the key controllers for blood pressure and cardiac output," said Mary Morrell, a physiologist at Imperial College, University of London. Lack of sleep can disrupt the blood flow around the body, leading to an increased risk of heart problems.

"An afternoon siesta in a healthy individual may act as a stress-releasing habit, and there is considerable evidence that stress has both short and long-term adverse effects on the incidence of and mortality from coronary heart disease," wrote Prof Naska.

Sleep deprivation has previously been linked to many problems. Several areas of the brain responsible for the regulation and control of sleep also influence appetite, leading bad sleepers to eat more; and irregular sleep can also cause brain degeneration.

"If you don't sleep properly, you can't encode memories properly," said Dr Morrell. "The most important thing is to regulate your sleep properly - go to bed at a regular time and get up at a regular time, which is something hardly any of us do.

"Sleep is such an under-recognised function. It has such a big impact on our ability to function during the day in terms of being able to encode memory and in terms of being alert. It's like being fit and doing exercise - it goes in the same bracket of health and wellbeing."