Researchers have long known that countries such as Greece, Italy and Spain, where people commonly take siestas, have lower rates of heart disease than would be expected. But previous studies that attempted to study the relationship between naps and heart disease have produced mixed results. The new study is first to try to fully account for factors that might confuse the findings, such as physical activity, diet and other illnesses.

"This study has a number of advantages," Trichopoulos said. He and colleagues at the University of Athens examined 23,681 Greek men and women ages 20 to 86 who had no history of heart disease or any other serious health problem when they enrolled in the study between 1994 and 1999. The researchers asked the participants whether they took midday naps and, if so, how often and for how long. They also asked detailed questions about their health and lifestyles, such as whether they had any illnesses that might make them sleep more, how much exercise they got and what they ate.

After an average of more than six years of follow-up, 792 of the study subjects died, including 133 who died of heart disease. Of that group, 94 were nappers. After the researchers accounted for factors that could confuse the issue, they found that those who took naps frequently were 34 per cent less likely to die of heart disease than those who did not. The biggest nappers -79 people who took a siesta for 30 minutes or more at least three times a week had a 37 per cent lower risk.