Children with inconsistent sleep schedules have higher body mass index (BMI) percentiles, according to research published in theĀ Annals of Behavioral Medicine.

“We’ve known for a while that physical activity and diet quality are very strong predictors of weight and BMI,” lead author Lauren Covington, an assistant professor in the University of Delaware School of Nursing, said in a statement.

“I think it’s really highlighting that sleep may be playing a bigger role here than it’s been given credit for.”

The study used data from an obesity prevention trial for mothers and their children living in Baltimore. All of the families were eligible for the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) and 70% were living at or below the poverty line. As part of the trial, 207 toddlers wore accelerometers that measured their sleep and physical activity for up to a week at a time. Mothers also completed a food diary that was compared with the Healthy Eating Index, a measure of diet quality based on the recommendations from the Dietary Guidelines for Americans.

Researchers wanted to examine the relationship between poverty and BMI, specifically looking at whether the consistency of when toddlers went to bed, their level of physical activity and diet quality could explain the association. They found that children from households with greater poverty had more overall inconsistent sleep onset times. And those with more inconsistent bedtimes had higher BMI percentages.

Covington said it is likely a bidirectional relationship. “There’s a lot of teasing out the relationships of the mechanisms that are at play here, which is really difficult to do because I think they’re all influencing each other,” she said.

Sleep recommendations suggest children go to bed within an hour of their usual bedtime on a nightly basis. But for families living in poverty, such scheduling may not be so easily done, Covington said, especially if a caregiver is the only parent, juggling multiple jobs, parenting multiple children or dealing with a tenuous housing situation.

“There’s so many factors that are at play and not necessarily controllable, especially in disadvantaged communities,” said Covington, who hopes in the future to develop interventions for families that support healthy routines.