If you had to guess whether watching too much television, not exercising, or sleeping too little is most likely to contribute to childhood overweight, what would you answer? Few people guess that those children who don't get enough sleep may be more at risk for overweight than if they watch too much television or forgo exercise.

A recent study reported in the International Journal of Obesity studied a group of 422 children between the ages of 5 and 10. Researchers questioned parents about lifestyle habits, such as average amount of time spent sleeping, watching television, and exercising. The study concluded that those who slept only 8-10 hours per night were much more likely to be overweight or obese than those who slept 12 or more hours per night. Children who watched television more than three hours daily were twice as likely to be overweight or obese than those who watched less TV and those who didn't exercise were only somewhat more likely to be overweight - but neither of these had as significant of an impact on body weight as skimping on sleep.

Why is this? Previous research has shown that a lack of sleep is associated with a lower level of leptin, a hormone that helps to reduce hunger, and increased levels of ghrelin, a hormone that increases hunger.

The study authors point out that more research is needed to confirm their findings, since this study was based upon interviews with parents rather than scientific measurements, such as electroencephalograms (EEGs) to measure actual time spent sleeping. That is, parents may have reported time of going to bed rather than time of falling asleep.

The amount of sleep time recommended by the American Academy of Pediatrics varies by age, but in general, 5-6 year olds need 10-12 hours sleep per night. Sleep needs decrease slightly with age; teens need an average of about 9 hours sleep nightly.