The study included nearly 2,200 kids in 20 U.S. cities. One-third of them had consistent, age-appropriate bedtimes between ages 5 and 9, according to their mothers.
Compared to that group, those who had no bedtime routine at age 9 got less sleep and had a higher body mass index (an estimate of body fat based on height and weight) at age 15, according to the Penn State study.
“Parenting practices in childhood affect physical health and BMI in the teenage years. Developing a proper routine in childhood is crucial for the future health of the child,” study co-author Orfeu Buxton said in a university news release.