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The latest study regarding the amount of sleep needed for adults confirms earlier research. The study, reported in Sleep (February 2004), found that individuals who sleep an average of 7 hours a night live the longest. For this particular study, Japanese researchers followed 104,010 adults for a decade. At the beginning of the study, the participants were asked to complete questionnaires about their sleep patterns and about their health, mental health, and lifestyle habits, which also can affect survival.
Yet, the ideal amount of sleep for each individual varies due to factors that are not completely understood, noted Daniel Kripke, MD, a sleep researcher at the University of California-San Diego School of Medicine. There is no evidence that shortening sleep from 8 to 7 hours will lengthen any specific individual's life. Genetics and other factors that also influence life span may play a role in an individual's sleep, he said.