SAN DIEGO, Oct. 2 (UPI) -- The secret to a long life may be getting a good night's sleep -- less than 5 hours a night is not enough, but 8 hours may be too much, U.S. researchers say.
Study leader Dr. Daniel F. Kripke, a professor emeritus of psychiatry at University of California, San Diego School of Medicine, revisited original research conducted from 1995 to 1999 as part of the Women's Health Initiative. Kripke and colleagues had tracked 459 women ages 50-81 living in San Diego to determine whether sleep duration could be associated with mortality. Fourteen years later, they checked on who was still alive.
Of the original participants, 444 were located and evaluated, while 86 women had died.
"The surprise was that when sleep was measured objectively, the best survival was observed among women who slept 5-6.5 hours," Kripke says in a statement. "Women who slept less than 5 hours a night or more than 6.5 hours were less likely to be alive at the 14-year follow-up."
This means that women who sleep as little as 5 to 6.5 hours -- the average measured sleep duration for San Diego women -- have nothing to worry about, since that amount of sleep is evidently consistent with excellent survival, Kripke says.
The findings are published online in the journal Sleep Medicine.
