June 14, 2006 -- The largest study to track the effects of sleep habits on weight gain in women found that those who on average sleep less, gain weight at a faster rate than women who sleep more.
Every two years for 16 years, 68,183 women ages 30 to 55 were asked to report their weight and habitual sleep duration. By the end of the study, women who slept 5 hours or less per night were more likely to experience major weight gain (defined as an increase of 33 pounds or more) and 15 percent more likely to become obese than those who slept 7 hours a night.
Those who slept 6 hours were 12 percent more likely to experience major weight gain and 6 percent more likely to become obese. Adults are considered obese if they have a Body Mass Index (BMI) of 30 or more and overweight if their BMI is greater than 25.
On average, researchers found that compared to women who slept seven hours per night, those who slept 5 hours or less gained 2.3 pounds more, and those who slept 6 hours gained 1.6 pounds more.
"That may not sound like much," notes lead researcher Sanjay Patel, MD, assistant professor of medicine at Case Western Reserve University in Cleveland, Ohio, but "even a small difference in weight can increase a person's risk of health problems such as diabetes and hypertension."
Interestingly, diet and exercise had nothing to do with the weight gain, according to the study, which was presented at the 2006 American Thoracic Society International Conference in San Diego, Calif.
As far as diet, Dr. Patel says on average the study found that "women who slept less consumed fewer calories than women who slept more, suggesting that the increased rate of weight gain was not due to eating more, but more likely due to burning fewer calories. Perhaps, the fatigue resulting from decreased sleep results in less calories burned."
In terms of exercise, women who slept more hours did exercise more, but the differences in physical activity were not substantial enough to explain why women who slept less weight more.
Further research is needed to understand why sleep duration may affect weight, Dr. Patel notes. So far, other studies support his findings and raise cause for concern.
"Younger groups may be even more at risk for the effects of sleep deprivation than older populations," he warns.
He cites a study by Gregor Hasler in Switzerland, which observed individuals as young as 19. The results showed much larger effects of sleep deprivation on weight gain than in his study, Dr. Patel points out.
A Canadian study went even further. It looked at children between the ages of 5 and 10 and found that those who slept eight to 10 hours nightly were three times more likely to be overweight than kids who slept 12 to 13 hours. The theory in this study is that sleep deprivation may cause an imbalance in hormones that affect weight.
What do you think of Dr. Patel's study? As a busy parent, do you get more than seven hours of sleep a night? Do you think there's a link between how much sleep you get and weight gain? Share your concerns with other moms on the Your Health message board below.
Sources: Sanjay R. Patel MD, MS; American Thoracic Society International Conference, San Diego, Calif., May 19 -24, 2006; "Rx for Obesity: Eat Less, Exercise More, and -- Maybe -- Get More Sleep," JAMA, May 24/31, 2006 - Vol. 295, No. 20.