Taking forty winks in the middle of the day may reduce the risk of death from heart disease, particularly in young healthy men, say researchers.

A six-year Greek study found that those who took a 30-minute siesta at least three times a week had a 37% lower risk of heart-related death.

The researchers took into account ill health, age, and whether people were physically active.

It is known that countries where siestas are common tend to have lower levels of heart disease, but studies have shown mixed results.

The researchers in the Greek study looked at 23,681 men and women aged between 20 and 86. The subjects did not have a history of heart disease or any other severe condition.

"This study has four advantages - it's large, prospective, limited to healthy people and we have been very careful to control for physical activity" said Dr Dimitrios Trichopoulos, from the Harvard School of Public Health

Participants were also asked if they took midday naps and how often, and were asked about dietary habits and physical activity.

The researchers found those who took naps of any frequency and duration had a 34% lower risk of dying from heart disease than those who did not take midday naps.

Those who took naps of more than 30 minutes three or more times a week had a 37% lower risk.

Among working men who took midday naps, there was a 64% reduced risk of death compared with 36% in non-working men, and researchers believe that this is due to the reduction in stress associated in taking a siesta.

Lead researcher Dr Dimitrios Trichopoulos, from the Harvard School of Public Health, said: "In countries where mortality from coronary diseases is low, siesta is quite prevalent."

"There have been other studies but with equivocal results."

"The thing we can say is that it's worth studying further."