Ask anyone who's dealt with a crabby toddler at the end of the day: Little kids need a lot of sleep. The National Sleep Foundation says that 1- to 3-year-olds, for example, generally need 12 to 14 hours of shut-eye a day.
Coming up short does more than put the whole family in a bad mood. Studies have suggested that both adults and kids who don't get enough sleep are more likely to carry extra pounds than those who do.
Researchers in Boston wanted to know whether that finding would hold for kids who regularly got less-than-ideal amounts of sleep during their early years. So they studied more than a thousand between the ages of 6 months and 7 years, getting annual reports from parents on the amount of sleep both at night and from daytime naps the kids got.
They also collected information on height and weight. And when the kids turned 7, researchers measured their overall and abdominal fat. (That's important, because belly fat appears to be more dangerous than fat elsewhere in the body.) The researchers found that getting less-than-recommended amounts of sleep was associated with a higher BMI and higher amounts of overall and midsection fat.
For example, after adjusting for factors including parental income, education and TV habits, a 7-year-old who got less than 12 hours of sleep between the ages of 6 months and 2 years had 36 percent higher odds of being obese than a child who got more sleep as a small child.
The study is noteworthy because it tracks sleep issues over a period of several years, says Dean Beebe, a neuropsychologist at Cincinnati Children's Hospital Medical Center who has studied sleep and diet in adolescence and wasn't involved in this research.
The study can't tell whether the missed sleep actually caused the kids to put on fat. It's possible that some factor the authors didn't account for was the real culprit. But there are several theories that might tie curtailed sleep to obesity, including the ebb and flow of hormones that control hunger.
Much of the research on mechanisms depends on findings in adults, and additional factors may be at play in kids, says Elsie Taveras, a pediatrician at MassGeneral Hospital for Children and lead author of the study. For example, a poor sleep routine at home also means that "eating and meal patterns are probably also disrupted in those homes," she says.
Until the link between sleep and weight is more fully understood, "there's no harm in trying to work with parents and young children to improve sleep," says Taveras. That includes a consistent bedtime, removing high-tech toys from the bedroom at night and other good habits.
"It can't hurt," says Beebe. "Inadequate sleep has a whole host of negative consequences."
The results of the study were published online by the journal Pediatrics.