Women who sleep five hours a night or less are more likely to pack on extra pounds, a recent American study shows.

    The study led by Dr. Sanjay Patel, professor of medicine at Case Western Reserve University in Cleveland, is the largest to date to follow the effects of sleep on weight over an extended period of time. He and his colleagues tracked more than 68,000 middle-aged women from 1986 to 2002.

    "This adds to growing evidence that it's important to allow yourself to get more sleep," said Patel, who presented the research Tuesday at the American Thoracic Society International Conference in San Diego.

    At the start of the study, the women who slept five hours or less already weighed 5.4 pounds more than those who slept longer.

    Although all the women gained weight over the 16 years, the women who slept five hours or less gained more, an average of 1.5 pounds, when the data were adjusted for various factors including caffeine intake, medication or alcohol use. Although this is a relatively small increase in weight, Patel said, the women's risk of developing obesity went up considerably.

    Sleep's possible contribution to obesity, an alarming worldwide pandemic, could add to rates of diabetes, hypertension and cancer.

    Some of the data also puzzled researchers: Women who slept less took in fewer calories than women who slept more. That means how many calories the women ate did not dictate how much they weighed. Similarly, the women's exercise patterns did not explain why the women who slept less weighed more.

    It could be the data was imperfectly measured, as it's hard to pinpoint exactly what people eat and exactly how many calories they expend, explained Dr. Emmanuel Mignot, Stanford's Howard Hughes Medical Institute investigator on sleep research. Enditem

    (Agencies)