The START study: An evaluation to study the impact of a natural experiment in high school start times on adolescent weight and related behaviors

Background:

Research has shown that early high school start times, which are asynchronous with adolescent biology, are one of the most significant obstacles to youth being able to net sufficient sleep. Given that adolescence is a critical period that sets the stage for long-term obesity risk behavior patterns, there is an need to understand the obesity-related implications of increased sleep as a result of intervention and policy changes.

Methods:

We evaluated a community-based natural experiment in school start time policy modification when several Minneapolis-St. Paul, MN metro area school districts shifted to later school start times in Fall 2016. We collected data on student weight and related risks (via paper survey, objective weight and height measurement, dietary recall, and sleep actigraphy) before and after two districts (two high schools) shifted their start times later and in a comparison district (three high schools) which kept their start times early (7:30am) through the course of the study. Our specific aims were: 1) Determine how a shift to a later high school start time relates to objectively measured weight change over time. 2) Identify the relationship between school start times and obesity-related behaviors over time.

At baseline we had 2,133 returned surveys (93% participation) and 2,037 (86% participation) objective height/weight measurements from 9th grade students (class of 2019) in the five schools. The sample was 87.7% white, 12.8% reported qualifying for free/reduced price lunch (a measure of lower socio-economic status), and the mean age was 15.2 (SD=0.35) years.

Discussion:

The products of this research will clarify causal connections between sleep and obesity among adolescents as well as provide evidence for whether a school start time policy can minimize unhealthy weight gain.