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 النوم ! دراسة علمية هدية للنوامات
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You Can't Fight Biological Clock
Internal Biological Clock Helps Explain a Wide Reaction to Alarm Clock
By Sid Kirchheimer
Reviewed By Michael Smith, MD
on Thursday, January 30, 2003
WebMD Medical News
Jan. 30, 2003 -- Your alarm clock may dictate how much sleep you get, but how much you need is determined by your internal biological clock. And despite the common notion that eight hours should translate to a quality 40 winks for the masses new research suggests that an individual's need for sleep is... well, individual.
While we all function on a 24-hour body clock, apparently some of us have longer "biological nights" -- the period in which hormonal and other changes occur that influence sleep, according to a study in the January issue of the Journal of Clinical Endocrinology & Metabolism. That may help explain why some people wrestle with the snooze button each weekday morning and even weekend afternoons, while others never even need it.
"Different people have different internal signals that dictate the amount of sleep they need," says study researcher Daniel Aeschbach, PhD, sleep specialist at Harvard Medical School and Brigham & Women's Hospital. "And once these signals are present, it is very difficult to change current sleep habits."
Researchers have long suspected that the need for sleep was driven by an internal signal, coupled with influence by "outside" factors such as daylight and meals. However, they really didn't understand why some people were natural "long" sleepers who seem to require nine or more hours a night, while other "short" sleepers function fine on fewer than six.
However, even when sleep-influenced factors such as daylight and meals are removed, Aeschbach says that "long sleepers" continue to have a longer biological night, an extended period in which melatonin and other hormones are secreted, body temperature lowers, and other physiologic changes occur. He learned this by measuring biological changes occurring in 10 "long" sleepers and 14 "short" sleepers who stayed awake for 40 continuous hours in a room in which they couldn't tell time or be influenced by other sleep "tip-offs."
"Since we can see that people who have an extended biological night need to sleep longer, we can see why it is difficult for them to change their sleep habits," he tells WebMD. Unfortunately, he says scientists only know that there are differences in individual sleep needs -- and don't know how to influence them so you can get away with getting less sleep.
Still, the finding raises an intriguing point, says Scott A. Rivkees, MD, pediatric endocrinologist at Yale University School of Medicine who wrote an editorial on Aeschbach's study. "If sleep needs vary individually, some people having more sleep may have health problems, just as having less sleep cause more problems," he tells WebMD.
Just last week, a study showed that women who got nine or more hours of sleep a night faced a greater risk of heart disease. In addition, the study showed that sleep deprivation can cause health problems as well.
"It is unhealthy in certain circumstances to oversleep on weekends in an effort to catch up on lost sleep," says Rivkees. "Basically, you need to listen to what your body is telling you. If you're waking up refreshed and not feeling tired during the day that suggests you are getting enough sleep. But if you have difficulty waking up, feeling tired, having to take naps, common sense tells you that you need more sleep at night. However, it is difficult to willfully change sleep habits and the hands of the circadian clock."
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SOURCES: Journal of Clinical Endocrinology & Metabolism, January, 2003 • Daniel Aeschbach, PhD, assistant professor of medicine, Harvard Medical School; division of sleep medicine, Brigham & Women's Hospital, Boston • Scott A. Rivkees, MD, associate professor of pediatric endocrinology and Director of Yale Child Health Research Center, Yale University School of Medicine, New Haven, Conn.
© 2003 WebMD Inc. All rights reserved.
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