The amount of sleep a child gets may vary according to the day or season, but those who are regularly sleep-deprived may have a higher risk of becoming overweight, new research suggests.

In a study that followed 591 children to the age of 7, researchers found that in general, children tended to sleep a little less on weekends than on weekdays, and during the summer compared with other months.

Those who were particularly “short sleepers” at age 7 were at greater risk of being overweight or having behavioral problems, the researchers report in the medical journal Sleep.

They found that children who slept less than 9 hours per night were three times as likely as longer sleepers to be overweight or obese.

Similarly, short sleepers were more likely to have behavioral issues and symptoms of attention-deficit/hyperactivity disorder, based on questionnaires given to parents and teachers.

The findings suggest that inadequate sleep may contribute to both weight and behavioral problems in young children, according to the researchers, led by Dr. Edwin A. Mitchell of the University of Auckland in New Zealand.

Past studies have hinted that insufficient sleep can encourage weight gain. Though the reasons aren’t clear, one theory is that sleep deprivation alters hormones involved in appetite control and metabolism.

In the current study, Mitchell pointed out, the link between sleep deprivation and weight remained when the researchers accounted for the children’s exercise habits and TV watching - two key factors in children’s risk of becoming overweight.

This suggests that there is a “real” effect of sleep deprivation on weight, he told Reuters Health.

In general, experts recommend that school-age children get 10 to 11 hours of sleep per night, while preschoolers should get 11 to 13 hours. On average, the 7-year-olds in the current study got 10 hours of sleep.

The findings, according to Mitchell’s team, underscore the importance of children getting the recommended amount of sleep.

“Our findings,” they conclude, “suggest that sleep duration may be at least in part a modifiable risk factor for other poor health outcomes in childhood, including obesity.”

SOURCE: Sleep, January 1, 2008.