Children who do not get enough sleep are often irritable and unable to concentrate in school.  But now a new study suggests lack of sleep could also contribute to the epidemic of childhood obesity in many countries.  VOA's Carol Pearson has more on that study and other research connecting sleepiness with obesity.

If children got to bed earlier and woke up later, fewer kids would be overweight. That is the conclusion of a newly published study on children and sleep. 

The study was conducted at Northwestern University. It followed more than 2,000 children from three to 18 years of age.

Researchers weighed the participants then checked them again five years later. The children or their parents kept sleep journals.

The researchers found children who slept less weighed more than those who got more sleep. Children who had just one extra hour of sleep each night were 20 percent less likely to be overweight five years later.  Later bedtimes play a greater role in overweight children between 3 and 8 years of age, while earlier waking times play a greater role in the weight of children aged 8 to 13.

Experts recommend that children under five get 11 to 13 hours of sleep each night; that children five to 12 get 10 to 11 hours of sleep, and that teenagers get nine hours.

Other research shows a connection between lack of sleep and the hormone that causes hunger.  In this study, where volunteers had their sleep curtailed, the hunger hormone, ghrelin, rose 24 percent.

Professor Eve Van Cauter at the University of Chicago says, "You're more hungry, even if you have the same amount of food.  And so you're more likely to over-eat and thus gain weight."

Both studies agree with what sleep specialist Dr. Beth Malow at Vanderbilt University has found: "This research is consistent with prior studies, it's relatively new, and it's really applicable for people of all ages."

The studies suggest sleep, at least more of it, could reduce the risk of being overweight and the medical problems that accompany weighing too much.