Parents have long been told that poor sleep habits and obesity are linked, a new study that finds there is more to the story.

The recently published research followed more than 350 children and assessed sleep, body mass index, or BMI, and cortisol levels.

Purdue University researchers were part of a national team that wanted to look at how the factors are related.

Kristine Marceau, assistant professor of human development and family studies at Purdue, says the study finds it is unlikely that poor sleep causes higher BMI.

“It’s more likely that other stable or habitual factors, like family routines or caregivers regulations of child health and habits lead to both better sleep and lower BMI,” says Marceau.

Marceau says that means interventions to improve sleep habits may not be an effective way to reduce weight. She says they found cortisol wasn’t a reliable factor in either poor sleep or high BMI.

“It seems like cortisol production was still really variable during early childhood, which just means that the stress response system is still developing,” says Marceau.

The study tracked levels of the stress hormone cortisol that is related to metabolism.