Each extra hour of sleep cuts a child's risk of becoming overweight or obese by nine percent, according to an analysis of epidiomogical studies by researchers from Johns Hopkins Bloomberg school of public health.

By contrast, children who got the least sleep had a 92 percent higher change of being overweight or obese than children who slept enough, said the study published in the Journal Obesity.

"Our analysis of the data shows a clear association between sleep duration and the risk for overweight or obesity in children. The risk declined with more sleep," said Youfa Wang, a senior author of the study.

"Desirable sleep behavior may be an important low cost means for preventing childhood obesity and should be considered in future intervention studies," Wang said in a news release.

"Our findings may also have important implications in societies where children do not have adequate sleep due to the pressure for academic excellence and where the prevalence of obesity is rising, such as in many East Asian countries."

The researchers reviewed 17 published studies on sleep duration and childhood obesity.

Some research recommends that children under five years old sleep 11 hours or more a day, while children age five to ten should get 10 or more hours of sleep, and children older than ten should sleep at least 9 hours.