Children who do not get enough sleep may increase their risk for obesity, a new study has found.

The researchers recorded sleep times and body mass index of 785 children in third grade and then again in sixth. Children slept an average of 9.45 hours a night in third grade and 8.78 in sixth.

After controlling for sex, race, maternal education, sleep problems like nightmares and other variables, the authors found that for every hour that sleep time declined over the three years, children were about 40 percent more likely to be overweight. The protective effect came mostly from earlier bedtimes rather than later wake times.

The authors concede that some unmeasured variables could have affected the results. For example, they write, parents may use food to pacify irritable sleep-deprived children, or sleep-deprived children may request and receive food more often.

Image Credit... Stuart Goldenberg

The reason for the association is unclear, but parents are apparently not to blame. “We examined lax parenting,” said Dr. Julie C. Lumeng, the lead author of the study, which appeared in the Nov. 5 issue of Pediatrics, “and lax parenting is not the explanation.”