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Research that reviewed 16 previous studies found that people who sleep more than eight or less than seven hours a night had a 30-percent greater risk of dying prematurely. While making sure you get enough sleep is a smart move, Knutson says people shouldn't get too worried about the health effects of oversleeping. In many cases, she says people who report sleeping for long periods have preexisting health problems or are saying they're sleeping when they're really just lying in bed.