Kids today tend to sleep less and weigh more than their peers growing up just a few decades ago. Now intriguing new research suggests this is no coincidence.

The survey of grade-schoolers in Quebec showed that the less the children slept the more likely they were to become overweight.

Children who routinely got 10 hours or less of sleep a night had almost 3.5 times the risk than those who got 12 hours or more. Lack of sleep was a bigger risk factor for overweight and obesity in the study than any other known contributor, including parental obesity, family income, or time spent in front of the television or computer.

Although the observational findings must be confirmed in clinical trials, study co-author Angelo Tremblay, PhD, says the evidence that sleep deprivation plays a role in obesity is mounting.

“It is ironic that part of the solution to obesity might lie in sleep, the most sedentary of all human activities,” he says. “In light of this study’s results, my best prescription against obesity in children would be to encourage them to move more and to make sure they get enough sleep.”

Twice as Many Overweight Kids

The rise in childhood obesity has been identified as a major public health concern in the industrialized world. There are twice as many overweight kids between the ages of 6 and 11 in the United States today than there were 20 years ago, and the number of teens who are overweight or obese has more than tripled.

At the same time, studies suggest that sleep deprivation is an increasing problem among children and adolescents.

While research also suggests that sleep deprivation may contribute to obesity among adults, few studies have investigated sleep patterns and weight in children.

The study by Tremblay and colleagues from Quebec’s Laval University included 422 grade-school students in Quebec. There were equal numbers of boys and girls with an average age of 6.5 for the girls and 6.6 for the boys. Researchers measured the children’s weight, height, and waist size, and information on sleep patterns and lifestyle was obtained through phone interviews with parents.

One in five boys in the study and about one in four girls were found to be overweight.

When compared with children reporting 12 to 13 hours of sleep a night, those that got 10.5 to 11.5 hours were more than 40% more likely to be overweight or obese, and those that got eight to 10 hours were almost 3.5 times as likely to be above normal weight.

The findings are reported in the latest online issue of the International Journal of Obesity.

Hormones May Hold the Key

If there is a link between sleep and weight regulation, many researchers now say that hormones may explain it. University of Chicago researchers have shown that sleep and lack of sleep affect production of two hormones that regulate appetite.

Their studies suggest that sleep deprivation was linked to lower levels of the hormone leptin, which decreases hunger, and higher levels of the hunger-producing hormone ghrelin.

Robert D. Vorona, MD, who has also studied sleep patterns and obesity in adults, says the research is fairly consistent but still inconclusive. He notes, for example, that there is no consensus on how much sleep people actually need to lower their risk of becoming overweight or to help them lose weight.

“What we can say is that the studies to date show an association between restricted sleep and obesity,” Vorona, who is the Eastern Virginia Medical School associate professor of medicine, tells WebMD. “What we can’t say is that these studies definitely prove a causal relationship.”

In a poll conducted in 2000, the National Sleep Foundation reported that the average American gets just under seven hours of sleep each night -- about an hour less than is optimal for most people and about 90 minutes less than most Americans slept in the 1900s.

Vorona says chronic sleep deprivation alters mood, affects performance, and is a major risk factor for automobile and work-related accidents.

“There are plenty of reasons to get a good night’s sleep,” he says. “And it is very possible that [weight control] is yet another one.”

By Salynn Boyles, reviewed by Louise Chang, MD

SOURCES: Chaput, J.P. International Journal of Obesity, online edition, March 14, 2006. Angelo Tremblay, PhD, professor, division of kinesiology, Laval University, Quebec, Canada; Canada research chairman in physical activity, nutrition and energy balance. Robert D. Vorona, MD, associate professor of internal medicine, Eastern Virginia Medical School, Virginia Beach, Va. WebMD Medical News: “Less Sleep Could Mean More Weight.” WebMD Medical News: “Sleep More and You May Control Eating More.” Weight statistics for children and adolescents, CDC.