Reviewer Youfa Wang, MD, PhD, an associate professor in the Center for Human Nutrition at Johns Hopkins University's Bloomberg School of Public Health, offers these tips for parents:
- Remove the TV, computer, and video games from kids' bedrooms. "Therefore, children can have more time to sleep rather than be tempted to engage in these activities," Wang tells WebMD.
- Set earlier bedtimes for kids. Wang suggests reading to young kids to help them get to sleep earlier.
- Beat the morning rush by preparing the night before. That way, the whole family can sleep a little bit later.
- Be a good role model for diet and exercise -- childhood obesity isn't just about sleep.
The review appears in February's edition of Obesity.
Children's Sleep: How Much Is Enough?
The new review used the following benchmarks for kids' sleep, including naps and nightly sleep, during a typical day:
- Younger than 5: at least 11 hours
- Ages 5-10: at least 10 hours
- Ages 10 and older: at least 9 hours
Those thresholds, which are based on previous research, may not apply to everyone.
"Some people, because of their own biological differences or their quality of sleep, may need fewer hours of sleep than others," Wang tells WebMD.
Studying Childhood Obesity and Sleep
In the reviewed studies, parents reported how long their young kids slept. Adolescents reported their own sleep habits.
Wang's team pooled all that data and compared it to the children's BMI ( body mass index), which relates height to weight.
Compared with kids who got enough sleep, those who fell at least two hours short of the sleep benchmarks were almost twice as likely to be overweight or obese.
Children who missed the sleep benchmark by an hour were 58% more likely to be overweight or obese than kids who got enough sleep.
"For each hour increase in sleep, the risk of overweight/obesity was reduced on average by 9%," the researchers write.
Why the Findings?
The reviewed studies were observational, so it's not clear which came first: extra pounds or less sleep.
It's also not clear how sleep affects children's weight. But Wang notes several theories:
- More time awake means more time to eat.
- Less sleep at night makes for drowsier, less-active days (and fewer calories burned).
- Sleep shortfalls may affect certain hormones. "This may increase people's feelings of hunger and also affect their energy expenditure," Wang says.
The links between sleep and BMI were stronger for boys than girls. The reason for that isn't clear, Wang says.
What About Genes?
"I think people should be aware of all the important potential risk factors," Wang says.
He points out that genes may only have their full effect when the conditions are right -- and in the case of obesity genes, that might mean being in a setting ripe with opportunities to overeat.
"It's a coin; which side do you want to pay more attention to?" Wang asks, putting genes on one side of the coin and environmental factors on the flip side.
"I think from a public health perspective, people should pay more attention to environmental and behavioral factors," Wang says. He notes that gene tests and gene therapy aren't yet available for obesity. And though you can't change your genes, behavior can bend.