A six-year study of nearly 24,000 Greek adults found those who regularly took midday naps lowered their risk of dying from heart disease by more than a third.

Those who made it a practice of napping at least three times a week for a minimum of 30 minutes had a 37 percent lower risk of dying from heart disease compared to non-nappers.

The relationship was even stronger among employed men as compared to unemployed men, with nappers apparently relieving some of the work-related stress that was bad for their hearts, researchers at the University of Athens Medical School and Harvard said.

The same conclusion could not be made for working women because of a limited number of subjects.

"We interpret our findings as indicating that among healthy adults, siesta, possibly on account of stress-releasing consequences, may reduce coronary mortality," lead author Androniki Naska wrote in 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," Naska wrote.

Occasional nappers were also less likely to die from heart problems than those who did not nap, but researchers said the benefit was not significant.

Out of 792 men and women who died during the follow-up period, 133 died from heart disease. Roughly half the subjects, who ranged in age from 20 to 86 and were not ill when the study began, took naps.

Unlike previous studies that have produced mixed findings on the heart benefits of napping, this study was based on people who died from heart problems, not on those who survived and would be more likely to nap.

DIET, EXERCISE, NAP

The latest study also controlled for the effect from smoking, diet and exercise. For example, Greeks are more likely to partake of a Mediterranean diet heavy in fish and nuts known to be healthy for the heart.

"If our results are valid, if they were to be confirmed, the benefit of naps would be comparable (to the benefits of the Mediterranean diet)," said the study's senior author, Dimitrios Trichopoulos of the Harvard School of Public Health.

"However, the effects of the Mediterranean diet, of red wine, and exercise are all proven. Whereas with the siesta, we only have this study," he said in a telephone interview.

"It would be foolish to claim that a nap was preferable to physical activity," he said.

Trichopoulos said another factor to consider is the so-called waking effect, where the risk of heart attack rises in the morning. Though not conclusive, some scientists believe the higher risk relates to awakening suddenly, triggering a surge in hormone secretions and blood pressure.

It was not known if waking suddenly from a nap posed a similar risk, but Trichopoulos downplayed it.

"I would say people who have been taking naps should continue to take them," he said.

"Here you have a benefit from an activity that has no side effects," he added, assuming an understanding boss.