Making sure kids get enough sleep may help them maintain a normal weight, a new study suggests.
Previous research had shown too little sleep may lead to changes in appetite and diet. In the new experiment, kids ate less and weighed less when they went to sleep earlier than usual, compared to when their bedtimes were pushed back.
But it was a small study - with only 37 kids ages eight to 11 - and lasted just three weeks.
"This is a small and brief study and the first experimental study that we are aware of with school-age children," Chantelle N. Hart said. She led the research at the Center for Obesity Research and Education at Temple University in Philadelphia.
"Additional studies need to be conducted prior to stating with certainty that sleeping more means eating less for kids," Hart said.
For the first week of her team's study, kids slept as usual - about nine and a half hours per night on most nights. That's below the recommended 10 to 11 hours for school-aged children, according to the National Sleep Foundation.
The researchers then split the kids into two randomly-selected groups. Children in one group went to sleep one and a half hours earlier than usual during the second week of the study. Those in the other group went to bed one and a half hours later than usual.
For the third week, those groups swapped routines.
During their week of extra sleep, kids ate an average of 134 fewer calories per day than during their shortened-sleep week, based on parents' reports.
They also weighed about half a pound less during the week they slept more, according to results published in Pediatrics.
It's hard to say how much of a difference 134 calories and half a pound really make, Hart said. The calorie estimates could have been biased, and every kid has unique energy needs and metabolism, she said.
Kids also had lower levels of the hormone leptin when they were getting more sleep. Leptin is produced by fatty tissue and believed to regulate fat storage in the body.
Some studies of adults have shown changing sleep duration can affect hormones that signal hunger or satiety. When people don't sleep as much, this would result in feeling hungrier and possibly eating more, Hart said.
This study begins to show sleep may directly affect weight, Dean W. Beebe said.
"And on one level that may be enough to take some real action, since we know that sleep is a behavior that can be changed," Beebe said.
He studies children, sleep and neuropsychology at Cincinnati Children's Hospital Medical Center in Ohio and wasn't involved in the new research.
"Even so, it would be good to know the mechanism, because it might help us to unravel the complicated puzzle of diet and weight management," he added.
It's exciting to think eating behaviors could be changed without dieting, he said.
"We can tell parents that we have even more evidence that sleep really is important," Beebe said. "Important enough to prioritize in the busy family schedule, to set and insist on a reasonable bedtime, to turn off the electronics like TV, video games, phones, iPads before bed, to push back against the onslaught of caffeinated products hitting the market, to reschedule activities so they don't run late into the evening - or reconsider if they are worth doing at all."
Parents might also lobby for sensible school schedules that don't start hours before adults - who need less sleep than children and teens - are expected to be at work, he said.
It will be important to do this study again with more kids over a longer period of time to see if the results are the same, Hart said. Researchers also need to figure out the best way to help kids sleep longer.
"A good night's sleep has been associated with a number of benefits for children across domains of functioning, including improvements in memory, learning and mood and decreased behavioral difficulties," she said. "The present study adds another potential benefit of a good night's sleep."