Preschoolers Who Sleep Less Weigh More by Age 7

May 26, 2011 -- How much sleep a child gets may affect their weight and their body fat.

That's according to a new study, published in BMJ. 

The study shows that found that preschoolers who are sleep less are more likely to be overweight or obese by the time they’re 7 years old, even when diet and other lifestyle factors are taken into account. 

And most of that added weight is stored fat, not muscle.

Sleep appeared to influence a child’s body weight more than both diet and physical activity. Only maternal weight mattered more, in the researchers' final analysis.

“The magnitude of the sleep effect was bigger than I expected,” says study researcher Barry Taylor, MBChB, head of the department of women and children’s health in the Dunedin School of Medicine at the University of Otago in New Zealand.

Experts who were not involved in the study say the findings are an important contribution, and if anything, probably underestimate the effect of sleep on weight.

“I think it’s consistent with what’s been seen in some of the other research that’s been focused on this age group,” says Michelle Garrison, PhD, a research scientist at Seattle Children’s Research Institute. “Poor sleep during the preschool ages really does seem to be associated with subsequent increased BMI scores.”

The study didn’t account for periods of time that children might spend awake in the middle of the night in their beds, Garrison points out.

“Night wakings can be pretty common in kids this age," she says. For example, she says a child that has a "sleep duration" of 11 hours might really have only slept for 9.5 of those hours, after taking the child's night wakings into account.

But "that difference doesn’t discount their findings," Garrison tells WebMD. If anything, I think if they had looked at true total sleep, the findings would have been even stronger,” Garrison tells WebMD.