A new study from Northwestern University shows that children who sleep less have a greater risk of being overweight, according to a new study. "Our study suggests that earlier bedtimes, later wake times, and later school start times could be an important and relatively low-cost strategy to help reduce childhood weight problems," said Emily Snell, co-author of the study.

In two waves of data collection approximately five years apart, researchers examined 2,182 children, using time diaries to record bedtime, time asleep, and wake time over the course of a weekday and weekend day.
The diaries helped researchers find troubling age-related trends in sleep behavior. By age seven, children were sleeping on average less than 10 hours on weekdays, and by age 14, weekday sleep time fell to 8.5 hours. A full 16% of adolescents (13-18) were found to sleep fewer than 7 hours on weekday nights. The National Sleep Foundation recommends children aged 5-12 years get 10-11 hours of sleep and adolescents get 8-9 hours of sleep.

The study's findings suggested that later bedtimes play a greater role in the overweight status of children aged from 3-8, while earlier wake times play a greater role in children 8-13. No significant differences in the effect of sleep on weight was found between boys and girls, nor was there evidence that children who slept more grew more in height. 

"We found even an hour of sleep makes a big difference in weight status," said Snell. "Sleeping an additional hour reduced young children's chance of being overweight from 36 percent to 30 percent, while it reduced older children's risk from 34 percent to 30 percent."

"Many American children are simply not getting the sleep they need. Parents, policymakers and health care providers all are concerned about the obesity epidemic among children," said Snell. " Our results suggest that something as simple as helping children sleep more at night could reduce their risk of being overweight."