Eight hours of sleep may not be so great

Doctors may recommend it for good health, but researchers now find that sleeping 8 to 9 hours a night doesn’t necessarily translate into a longer life.

Scientists came to that conclusion after analyzing medical and lifestyle data, including sleep reports, of 1.1 million people between ages 30 and 102 who had filled out questionnaires in 1982.

The researchers accounted for 32 factors, such as age, smoking, weight, economic status, exercise, and medications that might influence death rate in the group. When they assessed the volunteers’ status 6 years later, the scientists found a surprising trend.

People reporting 7 hours of sleep each night were the least likely to have died in the 6 intervening years, the researchers report in the February Archives of General Psychiatry. People sleeping 8 hours a night were 13 percent more likely to have died than the 7-hour sleepers. Volunteers getting 9 hours a night were 23 percent more likely to die than 7-hour sleepers were. On the other end of the sleep spectrum, people getting just 5 or 6 hours a night were 7 percent more likely than the 7-hours-a-night group to have died.

The study also found that people reporting insomnia were no more likely to have died during the 6 years of the study than those who didn’t, unless they were taking sleeping pills, says study coauthor Daniel S. Kripke, a psychiatrist at the University of California, San Diego, in La Jolla.

The findings should change the advice physicians give patients, Kripke says. If a person feels rested and alert after 5 or 6 hours of sleep, he says, doctors should tell that person that such a schedule poses little health risk.

The large number of people surveyed lends credibility to the findings, say Daniel J. Buysse and Mary Ganguli of the Western Psychiatric Institute and Clinic in Pittsburgh in the same journal.

However, they caution that the numbers don’t explain why some people slept more than others.

“And they certainly don’t tell us that it was the extra hour of sleep that killed them,” they say.

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