*The following is excerpted from an online article posted on MedicalXpress.
Little ones who stay up late may have a higher risk of becoming overweight by the time they are school-age, a new study suggests.
Researchers found that young children who routinely got to sleep after 9 p.m. tended to gain more body fat between the ages of 2 and 6. Compared with kids who had earlier bedtimes, they had bigger increases in both waist size and body mass index (BMI)—an estimate of body fat based on height and weight.
The findings do not prove that later bedtimes cause excess weight gain, said Dr. Nicole Glaser, who wrote a commentary accompanying the study, which was published online Feb. 18 in Pediatrics.
But the report adds to evidence linking sleep habits to kids’ weight, according to Glaser, a pediatric endocrinologist at the University of California, Davis.
Specifically, studies have found higher rates of obesity among kids who either get too little sleep or have trouble falling or staying asleep.
“At this point, I think it’s clear that there is a relationship between [sleep quality and obesity risk],” Glaser said. “The big question is whether the relationship is a causal one.”
The findings are based on 107 young children who were part of an obesity prevention project. Sixty-four had overweight or obese parents, so they were considered at high risk for excessive weight gain.
Between the ages of 2 and 6, kids’ sleep habits were recorded for one week each year, with the help of a wrist device that monitors activity.
On average, the study found, children who routinely went to bed after 9 p.m. showed somewhat greater gains in BMI and waist size over the years. The link was independent of total time asleep, and it remained even after the researchers accounted for factors like kids’ exercise habits and “screen time,” and parents’ education levels.
The connection was stronger among children whose parents were obese. Their waist size grew by an average of 3.5 centimeters (1.4 inches) more, compared to kids with earlier bedtimes and average-weight parents, the findings showed.