Getting enough sleep is healthful, but getting too much might not be.
Researchers gathered health and lifestyle information, including self-reported sleep data, on 116,632 people in 21 countries. Over eight years of follow-up, they recorded 4,381 deaths and 4,365 major cardiovascular events.
The study, in the European Heart Journal, found that compared with people who slept six to eight hours a night, those who slept eight to nine hours had a 5 percent increased risk for cardiovascular disease or death. People who slept nine to 10 hours had a 17 percent increased risk, and those who slept more than 10 hours increased their risk by 41 percent. The researchers also found a 9 percent increased risk in people who slept less than six hours, but that difference was not statistically significant.
Daytime naps also increased the risk for cardiovascular events, but only in people who slept more than six hours a night.
The researchers controlled for age, body mass index, physical activity, diabetes, depression, smoking, alcohol consumption and many other health and behavioral characteristics.
“Get enough sleep — that is, six to eight hours a day,” said the lead author, Chuangshi Wang, a doctoral student at McMaster University in Hamilton, Ontario. “But if you sleep more than nine hours a day, you may want to visit a doctor to check your overall health.”
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