Children who slept for fewer than nine hours a day were at increased risk of being overweight, indicated a study involving 3rd and 6th graders, reported in the journal Pediatrics. Gender, race, socioeconomic status or quality of the home environment did not alter the study results.

Strict Bed Time the Answer?

"Many children aren't getting enough sleep, and that lack of sleep may not only be making them moody or preventing them from being alert and ready to learn at school, it may also be leading to a higher risk of being overweight," says study lead author Julie C. Lumeng, MD, assistant research scientist at the U-M Center for Human Growth and Development.

"This study suggests that an increased risk for overweight is yet another potential consequence of short sleep duration, providing an additional reason to ensure that children are receiving adequate sleep, primarily through enforcing an age-appropriate bed time."

Even modest reductions in sleep duration are associated with significant increases in obesity risk among adults, according to recent studies.

The researchers reviewed data from the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development on reported sleep problems, sleep duration and BMI for 785 elementary school children, ages 9 to 12. Among those studied, 50 percent were male, 81 percent were white, and 18 percent were overweight in sixth grade.

The researchers found that overweight sixth-grade children slept fewer hours than children who were not overweight. Boys made up the majority of overweight sixth-grade children.

Boys, too, were reported to sleep fewer hours, while girls were found to have more sleep problems. Sleep problems, however, were not associated with a child being a risk for overweight.

One Hour Delivers Big Percentages

Most promising, these study results show that for every additional hour of sleep in sixth grade, a child was 20 percent less likely to be overweight in sixth grade; every additional hour of sleep in third grade resulted in a 40 percent decrease in the child's risk of being overweight in sixth grade.

Emerging research shows a connection between sleep disruption and the hormones that regulate fat storage, appetite and glucose metabolism. Short sleep duration alters carbohydrate metabolism and leads to impaired glucose tolerance, which can affect a person's weight. Circadian rhythms, too, affect the body's leptin, glucose and insulin levels.

"So weight gain may not be a result of sleep's effect on behavior, but rather sleep's effect on hormone secretion in the body, specifically, leptin and grehlin," says Lumeng, who notes that sleep and leptin secretion in children is an important area for future research.

The National Sleep Foundation recommends these basic daily sleep requirements for children, adolescents, pre-teens and teens: