By LEE BOWMAN
Scripps Howard News Service
May 23, 2006
The research was presented Tuesday at the American Thoracic Society's international conference being held in San Diego this week. It found that, on average, women who only got the five hours of shut-eye weighed 5.4 pounds more at the beginning of the study than those who slept seven hours. Additionally, the women getting fewer z's gained 1.6 pounds more than the others did over the next 10 years.
"That may not sound like much, but it is an average amount. Some women gained much more than that, and even a small difference in weight can increase a person's risk of health problems such as diabetes and hypertension," said Dr. Sanjay Patel, leader of the study and an assistant professor of medicine at Case Western Reserve University in Cleveland.
The study included 68,183 middle-aged women who were part of the Nurses Health Study, a 16-year tracking effort run by researchers at Harvard Medical School. During an initial survey in 1986, the women were asked about their typical night's sleep and then asked to report their weight every two years for the next 16 years.
Over the course of the 16 years, the researchers found that the women sleeping five hours a night or less were 32 percent more likely to experience major weight gain (adding 33 pounds or more) and 15 percent more likely to become obese than the women who got the seven hours of sleep.
Women getting only six hours nightly were 12 percent more likely to have major weight gain and 6 percent more likely to become obese than the seven-hour group.
Patel noted that "there have been a number of studies that have shown that, at one point in time, people who sleep less weigh more, but this is one of the first to show reduced sleep increases the risk of gaining weight over time."
The researchers say it's not clear why getting an extra hour or two of sleep matters so much in the weight-gain equation. They looked at diet and exercise habits for clues.
"Prior studies have shown that after just a few days of sleep restriction, the hormones that control appetite cause people to become hungrier, so we thought women who slept less might eat more. But in fact, they ate less,'' Patel said.
The researchers also checked women's responses to questions about exercise habits, but found no difference in the amount of jogging, running or other activity between the two groups that could explain why the women who slept less weighed more.
Patel said there are other possibilities that deserve further study.
"Sleeping less may cause changes in a person's basal metabolic rate (the number of calories you burn when you're at rest)," he suggested.
"Another contributor to weight regulation that has recently been discovered is called non-exercise-associated thermogenesis, or NEAT, which refers to involuntary activity, such as fidgeting or standing instead of sitting. It may be that if you sleep less, you move around less when you're awake, too, and therefore burn up fewer calories."
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