Middle-aged women may be able to sleep their way to a trimmer body, new study findings suggest.
In a study that followed more than 68,000 US women for 16 years, researchers found that those who caught more zzz's each night tended to put on less weight during middle-age.
What's more, women who typically clocked five hours of sleep were one-third more likely than those who slept for seven hours to have a substantial weight gain - 15kg or more - during the study period.
The findings, published in the American Journal of Epidemiology and presented this year at a medical conference, add to evidence that sleep habits affect a person's weight.
Although the reasons aren't clear, some research suggests that sleep deprivation alters hormones involved in appetite control and metabolism.
It's also possible that people who sleep fewer hours either eat more or, because of fatigue, exercise less often.
Whatever the reason, the new findings suggest that sleeping seven hours or more each night could help prevent middle-age spread, according to the study authors.
Dr Sanjay R. Patel of Case Western Reserve University in Cleveland led the research.
Dr Patel and his colleagues based their findings on data from the long-running Nurses' Health Study, which has followed the health of thousands of female nurses for the past 30 years.
On average, women who in 1986 said they usually slept five hours or less a night gained more weight over the next 16 years than those who slept for seven hours a night or longer.
Although the effect was modest, Dr Patel's team notes, even a relatively small weight gain can make a health difference; putting on an extra 5kg has been shown to double a person's risk of diabetes, for example.
And some of the weight gain was substantial. Sleep-deprived women were more likely to gain more than 14kg and were 15 per cent more likely to become obese as they grew older.
Consuming extra calories could not be blamed for the weight gain, the investigators add, because women who slept less also ate less.
