The impact of delayed school start time on adolescent beverage consumption, findings from the START study.

Objectives: We sought to examine the effects of high school start time delay, a proven sleep-promoting intervention, on sugary beverage (SB) consumption among U.S. adolescents.

Methods: In the Spring of 2016 (baseline), the START study recruited 2134 ninth grade students who were enrolled high schools in the Twin Cities, MN metropolitan area. These participants were surveyed again in their 10th and 11th grade years, in Spring 2017 and 2018 (follow-ups 1 and 2). All five high schools started early (7:30 or 7:45 a.m.) at baseline. By follow-up 1, two "policy change" schools shifted their start times later (8:20 or 8:50 a.m.) and maintained these later start times through follow-up 2 while three "comparison schools" retained an early start time at all time points. Generalized estimating equations using a negative binomial distribution were used to obtain estimates of the number of sugary beverages consumed per day at each wave as well as the difference in difference (DiD) estimates between baseline and each follow-up period comparing policy change to comparison schools.

Results: Mean baseline sugary beverage consumption was 0.9 (1.5) beverages per day in policy change schools and 1.2 (1.7) beverages per day in the comparison schools. While there was no evidence of impact of start time change on total SB consumption, DiD estimates revealed a small decrease in the number of caffeinated sugary beverages consumed between baseline and the second follow-up period in students attending the policy change schools relative to comparison schools in both crude (0.11/day reduction, p-value = 0.048) and adjusted analyses (0.11/day reduction, p-value = 0.028).

Conclusion: Although the differences in this study were quite modest, a population-wide reduction in sugary beverage consumption could have public health benefit.