Impact of delaying high school start times on weight and related behaviors - the START study

• Published in: Preventive medicine Vol. 172; p. 107548
• Main Authors: Widome, Rachel, Erickson, Darin J., Laska, Melissa N., Berger, Aaron T., Lenk, Kathleen M., Iber, Conrad, Kilian, Gudrun, Lammert, Sara, Wahlstrom, Kyla L.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.07.2023
• Subjects: Adolescent; Adolescents; BMI; Body Mass Index; Health Behavior; Humans; Natural experiment; Obesity; Overweight; School policy; School start time; Schools; Sleep; Time Factors; School policy; Obesity; School start time; Adolescents; Overweight; BMI; Natural experiment
• ISSN: 0091-7435; 1096-0260; 1096-0260
• DOI: 10.1016/j.ypmed.2023.107548

In the US, few adolescents get adequate school night sleep, largely due to early school start times. In the START study we aimed to test the following hypothesis: That following the implementation of later high school start times students have lesser longitudinal increases in body mass index (BMI) and shift to more healthful weight-related behaviors relative to students attending schools that retain early start times. The study enrolled a cohort of students (n = 2426) in five high schools in the Twin Cities, MN metro. Heights and weights were measured objectively, and surveys were administered annually from 9th through 11th grades (2016–2018). All study schools started early (either 7:30 am or 7:45 am) at baseline (2016). At follow-up 1 (2017) and continuing through follow-up 2 (2018), two schools delayed their start times by 50–65 min, while three comparison schools started at 7:30 am throughout the observation period. Using a difference-in-differences natural experiment design, we estimated differences in changes in BMI and weight-related behaviors over time between policy change and comparison schools. Students' BMIs increased in parallel in both policy change and comparison schools over time. However relative to changes in comparison schools after the start time shift, students in policy change schools had a modestly more healthful profile of weight-related behaviors – for instance they had a relatively greater probability of eating breakfast, having supper with their family, getting more activity, eating fast food less frequently, and eating vegetables daily. Later start times could be a durable, population-wide strategy that promotes healthful weight behaviors. •Later high school start times did not reduce risk of weight gain for adolescents.•Later start times led to more favorable trajectories of weight-related behaviors.•Population-wide strategies that promote healthful sleep among teens are needed.