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An Average Seven Hours of Sleep is the Best The truism that all adults need at least eight hours of sleep a night for good health should be put to rest by mounting evidence that less may be better.
Three huge studies have found that people who sleep about seven hours a night live the longest. In the latest report from Japanese researchers,104,010 adults were followed for about 10 years. At the start, the participants answered questionnaires about their sleep patterns, and about their health, mental status and lifestyle habits, which also can affect survival.
After accounting for all of these factors, adults getting an average of seven hours had the lowest death rates. Surprisingly, less sleep, even as little as four hours a night, didn’t significantly increase deaths for men and only lowered survival for women if they averaged less than four hours. But adults who slept longer than seven hours, particularly women, were more likely to die during the 10 years.
Doctors shouldn’t tell all of their patients to get at least eight hours of sleep, says psychiatrist Daniel Kripke, a sleep researcher at the University of California--San Diego School of Medicine in an editorial in the journal Sleeping. Because hormonal changes triggered by darkness or other unknown biological effects from long sleep could be affecting survival.