New research from a Singapore - U.S. team provides more evidence that sleeping too little - or too much - may be bad for your heart. The investigators also noted that diabetes and hypertension may contribute to this relationship.

Among 58,044 men and women 45 years of age or older without heart disease at study entry, those who slept 5 hours or less or 9 hours or more, were significantly more likely to die from cardiovascular disease over the next several years than people who logged 7 hours a night, Dr. Anoop Shankar of the West Virginia School of Medicine in Morgantown and colleagues found.

These findings back the results of other studies that have suggested how long people sleep may be a key predictor of their heart disease risk, Shankar and his team report in the American Journal of Epidemiology.

Most research on sleep duration and heart disease has been in Western populations, aside from three studies in Japan, the researchers note. Asian populations may have lower average body weights, different lifestyles, and different dietary exposures, compared with those in Western populations, that may affect their risk of cardiovascular disease, they add.

To investigate, the researchers looked at people participating in the Singapore Chinese Health Study. The study participants, who were ethnic Chinese living in Singapore, were enrolled between 1993 and 1998, and followed through the end of 2006. During that time, 1,416 people died of heart disease.

Thirty-three of the study participants said they got 7 hours of sleep a night. People who slept for 5 or less or 9 or more hours were more likely to have several different heart disease risk factors than those who slept for 7 hours, such as smoking and eating fewer fruits and vegetables and more fat and cholesterol.

But even after the researchers adjusted the data to account for these risk factors, they found that people who slept 5 hours or less were 57 percent more likely to die of heart disease, while people who slept 9 hours or more were at 79 percent greater risk.

Some investigators have suggested that sleeping longer may indicate underlying poor health, Shankar and his colleagues note. They attempted to address this fact by eliminating the first 4 years of follow-up from their analysis, as well as excluding people with diabetes or hypertension. In both cases the results were about the same, suggesting that sleep duration, not ill health, was behind the relationship with heart disease.

But when they included people with diabetes and hypertension in their analysis, treating these conditions as risk factors, the researchers found the link between sleep duration and heart disease mortality weakened. This suggests, they say, that diabetes and hypertension - both of which have been tied to sleep duration as well as heart disease death risk - may help explain the relationship between sleep duration and heart disease mortality.

SOURCE: American Journal of Epidemiology, December 15, 2008.