Dr. Sanjay Patel of Case Western Reserve University reported at a San Diego medical conference today that women who fail to get enough sleep at night risk gaining weight.

In a long-term study of middle-aged women, those getting 5 hours of sleep or less per night were 32% more likely to gain a significant amount of weight (33 lbs or more) and 15% more likely to become obese during 16 years of follow-up than women sleeping 7 hours each night.

This level of weight gain is “very clinically significant in terms of risk of diabetes and heart disease,” Patel told Reuters Health.

The study also found that women sleeping 6 hours a night were 12% more likely to experience a significant amount of weight gain and 6% more likely to become obese compared to those getting at least 7 hours of sleep a night.

The study observed 68,183 women in 1986 who reported their typical night’s sleep and reported their weight every 2 years for 16 years. The findings were presented at the American Thoracic Society’s International Conference.

Women reporting 5 hours or less sleep each night, on average, weighed 5.4 lbs more at the beginning of the study than those sleeping 7 hours or more.

After accounting for the influence of age and weight at the study’s induction, women who slept 5 hours or less per night gained about 2.3 lbs more during the follow-up than those sleeping 7 hours nightly. Women getting 6 hours of slumber per night gained about 1.5 lbs more than the 7-hour sleepers.

Patel and his research team analyzed the diets and physical activity levels of the women, but failed to find any differences that could explain why women getting less sleep weighed more. He explained, “We actually found that women who slept less, ate less.”

He concluded that it seems diet and exercise are not accounting for the weight gain in women who get less sleep.

He goes on to say that it’s possible that sleeping less may affect changes in a person’s basic metabolic rate – the number of calories burned when at rest.

Another possibility that’s recently surfaced is called “non-exercise associated thermogenesis” or NEAT, referring to involuntary activity such as fidgeting or standing instead of sitting. It could be, Patel noted, that if people who sleep less, also move around or “fidget” less.

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