Impact of a year‐round school calendar on children's <scp>BMI</scp> and fitness: Final outcomes from a natural experiment
R. Glenn Weaver, Ethan T. Hunt, Bridget Armstrong, Michael W. Beets, Keith Brazendale, Gabrielle Turner‐McGrievy, Russell R. Pate, Alberto Maydeu‐Olivares, Brian E. Saelens, Shawn D. Youngstedt, Roddrick Dugger, Hannah Parker, Lauren von Klinggraeff, Alexis Jones, Sarah Burkhart, Layton Ressor‐Oyer
Abstract
BACKGROUND: Structure may mitigate children's accelerated summer BMI gain and cardiorespiratory-fitness (CRF) loss. OBJECTIVES: Examine BMI and CRF change during school and summer for year-round and traditional calendar school children. METHODS: Three schools (N = 2279, 1 year-round) participated in this natural experiment. Children's BMI z-score (zBMI) and CRF (PACER laps) were measured from 2017 to 2019 each May/August. Mixed effects regression estimated monthly zBMI and CRF change during school/summer. Secondary analyses examined differences by weight status and race. Spline regression models estimated zBMI and CRF growth from kindergarten-sixth grade. RESULTS: Compared to traditional school, children attending a year-round school gained more zBMI (difference = 0.015; 95CI = 0.002, 0.028) during school, and less zBMI (difference = -0.029; 95CI = -0.041, -0.018), and more CRF (difference = 0.834; 95CI = 0.575, 1.093) monthly during summer. Differences by weight status and race were observed during summer and school. Growth models demonstrated that the magnitude of overall zBMI and CRF change from kindergarten-sixth grade was similar for year-round or traditional school children. CONCLUSIONS: Contrary to traditional school children zBMI increased during the traditional 9-month school calendar and zBMI decreased during the traditional summer vacation for year-round school children. Structured summer programming may mitigate accelerated summer BMI gain and CRF loss especially for overweight or obese, and/or Black children.