ScienceDaily (Oct. 1, 2010) -- A new study, derived from novel sleep research conducted by University of California, San Diego researchers 14 years earlier, suggests that the secret to a long life may come with just enough sleep. Less than five hours a night is probably not enough; eight hours is probably too much.
A team of scientists, headed by Daniel F. Kripke, MD, professor emeritus of psychiatry at UC San Diego School of Medicine, revisited original research conducted between 1995 and 1999. In that earlier study, part of the Women's Health Initiative, Kripke and colleagues had monitored 459 women living in San Diego (ranging in age from 50 to 81) to determine if sleep duration could be associated with mortality.
Fourteen years later, they returned to see who was still alive and well.
Of the original participants, 444 were located and evaluated. Eighty-six women had died. Previous studies, based upon questionnaires of people's sleep habits, had posited that sleeping 6.5 to 7.5 hours per night was associated with best survival. Kripke and colleagues, whose 1990s research had used wrist activity monitors to record sleep durations, essentially confirmed those findings, but with a twist.
"The surprise was that when sleep was measured objectively, the best survival was observed among women who slept 5 to 6.5 hours," Kripke said. "Women who slept less than five hours a night or more than 6.5 hours were less likely to be alive at the 14-year follow-up."