The researchers didn't calculate how many years earlier the subjects died if they had abnormal sleeping patterns. The study also doesn't make it clear if night owls or early birds are at risk, although that could explain why some of the men were active at early or late times of day, Paudel said.
Why would abnormal sleep patterns make death more likely? "We don't really know how this is related to mortality," Paudel said. "It could be that there is some other medical condition that wasn't accounted for."
Sleep researcher Dr. Daniel Kripke said early or late sleep patterns may disrupt the body's metabolism or reflect cases of Alzheimer's disease. It's also possible that unusual sleep patterns could reflect problems in the body's genes, said Kripke, a professor of psychiatry at the University of California at San Diego, who plans to collaborate on future research with one of the study's authors.
Kripke isn't ready to advise older men to adjust their sleep patterns. "As yet, there is no evidence in this type of person that changing a person's hours would improve survival," he said. "It means it is not a bad idea to have normal hours, but we cannot yet say that not having them is a willful mistake."
Learn more about sleep from the National Sleep Foundation.
SOURCES: Misti Paudel, M.P.H., research fellow, University of Minnesota-Twin Cities, Minneapolis; Daniel Kripke, M.D., professor, psychiatry, University of California, San Diego; June 11, 2008, presentation, Associated Professional Sleep Societies annual meeting, Baltimore
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