The research showed a clear association between long duration sleep and high mortality rates. But at present, the United States scientists who conducted the investigation cannot explain their findings. Dr Daniel Kripke, a professor of psychiatry at the University of California in San Diego, said: "We don't know if long sleep periods lead to death. Additional studies are needed to determine if setting your alarm clock earlier will actually improve your health.
"Individuals who now average 6.5 hours of sleep a
night can be reassured that this is a safe amount of sleep. From a
health standpoint, there is no reason to sleep longer." Scientists were
discussing the findings today at the annual meeting of the American
Association for the Advancement of Science in Boston, Massachusetts.
The advice flies in the face of the popular belief that eight hours' sleep a night is necessary to stay alert and healthy. Former Prime Minister Margaret Thatcher was famous for getting by on only four hours a night. That may be too little for ordinary mortals, the findings suggest. But even people who slept as little as five hours a night lived longer than participants who got more than eight hours a night.
The best survival rates were among individuals who slept seven hours a night. The results showed that a group sleeping eight hours were 12% more likely to die within the six year period covered by the study than those sleeping seven hours. Between 1982 and 1988, a total of 5.1% of the women taking part and 9.4% of the men had died.
There was nothing out of the ordinary about the causes of death. The study, a collaboration between the University of California and the American Cancer Society, was published today in the Archives of General Psychiatry. With 1.1 million participants, it was the first large-scale population study of sleep to take into consideration variables such as age, diet, exercise, previous health problems and risk factors such as smoking.
The findings also showed that occasional bouts of insomnia were not linked to higher death rates. But people who took sleeping pills were more likely to die sooner. "Insomnia is not synonymous with short sleep," the authors wrote. "Patients commonly complain of insomnia when their sleep durations are well within the range of people without sleep problems."
The advice flies in the face of the popular belief that eight hours' sleep a night is necessary to stay alert and healthy. Former Prime Minister Margaret Thatcher was famous for getting by on only four hours a night. That may be too little for ordinary mortals, the findings suggest. But even people who slept as little as five hours a night lived longer than participants who got more than eight hours a night.
The best survival rates were among individuals who slept seven hours a night. The results showed that a group sleeping eight hours were 12% more likely to die within the six year period covered by the study than those sleeping seven hours. Between 1982 and 1988, a total of 5.1% of the women taking part and 9.4% of the men had died.
There was nothing out of the ordinary about the causes of death. The study, a collaboration between the University of California and the American Cancer Society, was published today in the Archives of General Psychiatry. With 1.1 million participants, it was the first large-scale population study of sleep to take into consideration variables such as age, diet, exercise, previous health problems and risk factors such as smoking.
The findings also showed that occasional bouts of insomnia were not linked to higher death rates. But people who took sleeping pills were more likely to die sooner. "Insomnia is not synonymous with short sleep," the authors wrote. "Patients commonly complain of insomnia when their sleep durations are well within the range of people without sleep problems."