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May 24 (foodconsumer.org) - Women who sleep less during the night tend to gain weight over the years, found a new study suggesting that having enough night's sleep may help women stay slim.

Women who sleep 5 hours or less per night gain more weight on average than those who sleep 7 hours, according to the study presented at the American Thoracic Society International Conference May 23.

Sanjay Patel, M.D., assistant professor of Medicine at Case Western Reserve University in Cleveland, Ohio and colleagues followed 68,000 middle-aged women who were enrolled in the Nurses Health Study for their night's sleep and weight gain every two years for 16 years.

At the end of study, women who slept for 5 hours per night were 32% more likely to experience major weight gain (defined as an increase of 33 pounds or more), compared to those who slept 7 hours per night.

Additionally, those light sleepers were 15% more likely to become obese over the course of the 16-year study, compared with women who have a habit of sleeping 7 hours per night.
Women who had 6-hour sleep per night still faced a risk. They were 12% more likely to have major weight gain and 6% more likely to become obese, compared with women who slept 7 hours a night.

The risk of weight gain elevated by reduced sleep remains after the influence of age and weight at the beginning of the study was considered.

With age and starting weight considered, women who slept 5 hours or less each night gained about 2.3 pounds more during the follow-up than those who had 7-hour night’s sleep. Women who got 6 hours of shut-eye each night gained 1.5 pounds more than those who slept 7 hours nightly.

In terms of weight gain, insufficient sleep may have a bigger impact on some women. Some gained much more weight than others in the same group of light sleepers.

On average, women who slept 5 hours or less per night weighed 5.4 pounds more at the beginning of the study than those sleeping 7 hours and gained an additional 1.6 pounds more over the next 10 years.

"Some women gained much more than that (1.6 pounds), and even a small difference in weight can increase a person's risk of health problems such as diabetes and hypertension," Patel said.

This is the largest study to track the effect of reduced sleep on weight gain over time, Dr. Patel noted. "There have been a number of studies that have shown that at one point in time, people who sleep less weigh more."

In an attempt to explain those light sleepers gained more weight, the researchers looked at the women's d iet and e xercise habits to see if they could account for part of the findings.

"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 that women who slept less might eat more. But in fact they ate less," Dr. Patel said.

"That suggests that a ppetite and d iet are not accounting for the weight gain in women who sleep less." Patel added.

Women were also surveyed for their e xercise activities. But the researchers didn't find any difference in physical activity that could explain why women who had less sleep had more weight gain.

A scientist affiliated with foodconsumer.org, who doesn't want to be named, suggests that the d iet and physical activity was self-reported and subject to bias and errors, meaning these factors can't be excluded.

Weight gain is affected by many factors and we are not even certain that reduced sleep is a cause, he says. Earlier studies have found deprived sleep results in altered endocrine physiology, which affects a person’s appetite and metabolism, which seems to offer a logical explanation.

"Sleeping less may affect changes in a person's basal metabolic rate (the number of calories you burn when you rest)," Dr. Patel acknowledged.

"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, too, and therefore burn up fewer calories," Patel added.

Regardless of the cause, the association between reduced sleep and weight seems to be real. It s only unknown whether being over weight shortens a sleep span or sleeping less causes weight gain. The current study did not address other factors such as social status determining different lifestyles, which in turn can affect weight.

An study presented in November, 2004 at a meeting of the North American Association found that people who sleep 2 to 4 hours a night were 73 percent more likely to be obese than normal sleepers.

Another study published in December 2004 in the journal Public Library of Science involved 1,000 people in the Wisconsin Sleep Cohort Study also found that the less people sleep, the more weight they weigh. The study was conducted by Dr. Emmanuel Mignot of Stanford University in California and colleagues.

Excess weight and sleep d eficiency per se can cause a series of health problems. 63 percent of Americans do not get eight hours of sleep a night, and 65 percent are over weight or o bese, a sign suggesting that both go side by side.

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