Putting children to bed earlier may be a simple way to keep their weight down, research has shown.
Childhood obesity is not only caused by fast food, sugary drinks and lack of exercise, the new findings suggest. Lack of sleep also appears to be an important factor.
Scientists made the discovery after adjusting the sleep patterns of 37 children aged eight to 11, more than a quarter of whom were overweight or obese.
For the first week of the study, children were asked to sleep their typical amount. During the second week the children randomly had their sleep time either reduced or lengthened. Over the course of the third week, they were given the opposite sleep schedule.
When children increased their sleep, they reported consuming an average 134 fewer calories per day and lost half a pound in weight.
Tests showed they had lower fasting levels of the hunger-regulating hormone leptin.
"Findings from this study suggest that enhancing school-age children's sleep at night could have important implications for prevention and treatment of obesity," said Dr Chantelle Hart, from Temple University in Philadelphia. "The potential role of sleep should be further explored."
The findings are published in the journal Pediatrics.
Dr Hart is now working on a follow-up study to determine whether increased sleep produces significant changes in eating patterns, activity, and weight.
"Given all of its documented benefits, in many ways, you can't lose in promoting a good night's sleep," she added.