Ecologic Association Of School Start Time With Physical Activity Amongst U.s. High School Students

The American Academy of Pediatrics recommends that middle and high schools start at 8:30 am or later to allow students time for sufficient sleep to support health, academic performance, and quality of life. Given the high and increasing prevalence of adolescent obesity, the potential impact of school start time on obesity-related behaviors such as physical activity (PA) needs to be understood. PURPOSE: To determine the association of school start time with adolescent physical activity. METHODS: Public high school start time data for each state was obtained from the National Center for Education Statistics and the School Questionnaire of the National Teacher and Principal Survey (NTPS) in 2011-2012 and 2017-2018. Adolescent PA data were obtained from the Youth Risk Behavior Surveillance Survey (YRBSS) State level data from the 2011-2012 and 2017-2018 cycles (NTPS and YRBSS data were jointly available from 41 states). Using an ecological study design, complex survey logistic regression was used to examine the association while controlling for sex, grade, race, obesity indicator and survey cycle year. RESULTS: Among included states, median school start time was 8:02 am (range: 7:30 - 8:50 am). Approximately 16% of high school students reported zero days with ≥60 minutes of PA and only 25% of students met PA guideline recommendations of ≥60 minutes of daily PA. In comparison to 8:00 am, both earlier and later school start times were associated with increased odds of zero days with 60-minutes of PA as well as reduced likelihood of meeting PA recommendations. Specifically, students from states with average school start times of 7:30 am and 8:30 am had, on average 1.48 (95% CI for OR: 1.27-1.74) and 1.36 (CI: 1.19-1.55) greater odds of reporting zero days of PA compared to students from states with 8:00 am average start times, respectively. Conversely, 7:30 am and 8:30 am average start times were associated with 26% (CI: 15% - 36%) and 20% (CI: 9 - 30%) lesser odds of meeting PA recommendations compared with an 8:00 am start time, respectively. CONCLUSIONS: While 8:30 am or later high school start time may be beneficial to student sleep and academic performance, start times both later and earlier than ~8:00 am may hinder students’ ability to obtain sufficient physical activity. This trade-off merits further investigation.