A new study, “Sleep and adiposity in children from 2 to 6 years of age,” published in Pediatrics, found that no matter how much a child slept, going to bed late was associated with increased risk of obesity and higher body-mass index (BMI). Going to be late was defined by researchers as sleep onset after 9 pm.

Researchers followed 107 children, ages 2-6, from the Early Stockholm Obesity Prevention Project using a wrist-worn actigraphy, to record child’s sleep for seven consecutive days every year.

Forty-three had normal-weight parents and 64 had overweight and/or obese parents, which is linked to greater risk of obesity in children. While children of overweight and/or obese parents were more likely to be overweight, the study found that these children did not sleep differently than their peers.

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The study found that children, ages 2-6, who more frequently stayed up later at night (9 pm or later) had greater increases in both BMI and waist circumference, particularly in those children of overweight and/or obese parents.

Other concerning sleep-related issues, including short sleep duration, low sleep efficiency and irregular sleep, didn’t significantly increase the risk of gaining more weight. Researchers concluded that children, ages 2-6, who more frequently were awake after 9 pm had greater risk of gaining more weight, particularly in children at greater risk due to having obese parents. More research is needed to examine other potential impacts, including diet and exercise, due to the small sample size in this study, authors say.

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