外刊文章来源——《时代周刊》
　　Older people need less sleep 'a myth'
　　The popular notion that older people need less sleep than younger adults is a myth, scientists said yesterday.
　　While elderly people tend to sleep for fewer hours than they did when they were younger, this has a negative effect on their brain's performance and they would benefit from getting more, according to research.
　　Sean Drummond, a psychiatrist at the University of California, San Diego, said that older people are more likely to suffer from broken sleep, while younger people are better at sleeping efficiently straight through the night.
　　More sleep in old age, however, is associated with better health, and most older people would feel better and more alert if they slept for longer periods, he said.
　　"The ability to sleep in one chunk overnight goes down as we age but the amount of sleep we need to function well does not change," Dr Drummond told the American Association for the Advancement of Science conference in San Diego.
　　"It's definitely a myth that older people need less sleep. The more healthy an older adult is, the more they sleep like they did when they were younger. Our data suggests that older adults would benefit from continuing to get as much sleep as they did in their 30s. That's different from person to person, but the amount of sleep we had at 35 is probably the same amount we need at 75."
　　In his research, Dr Drummond has compared the sleep patterns of 33 adults with an average age of 68 with 29 younger people with an average age of 27. They had their brains scanned with functional magnetic resonance imaging, while they memorised a list of nouns.
　　"Older people who got less than six hours were the ones whose brains could not turn on the areas needed to memorise things," he said. "Older brains look sleep deprived and the question is, are they really sleep-deprived. Our data suggests that yes, sleep does impact performance and brain function."
　　The absolute number of hours spent asleep matters more for older people, while for younger people sleep quality is more important, Dr Drummond said. "If you were to fall asleep, never wake up until the alarm goes off and then jump out of bed, you have 100 per cent sleep efficiency. In older adults that happens less and less frequently. The most common characteristic of sleep as we age is that you wake up in the middle of the night.
　　"There's data to suggest that what breaks down as we age is not the need to sleep but the ability to sleep in a solid chunk. As we age the strength of our circadian rhythms breaks down. It's harder to be awake during the day and to be asleep at night."

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