Impact of a year‐round school calendar on children's BMI and fitness: Final outcomes from a natural experiment

• Published in: Pediatric obesity 2021-10, Vol.16 (10), p.e12789-n/a
• Main Authors: Weaver, Robert Glenn, Hunt, Ethan, Armstrong, Bridget, Beets, Michael W., Brazendale, Keith, Turner‐McGrievy, Gabrielle, Pate, Russell R., Maydeu‐Olivares, Alberto, Saelens, Brian, Youngstedt, Shawn D., Dugger, Roddrick, Parker, Hannah, Klinggraeff, Lauren, Jones, Alexis, Burkhart, Sarah, Ressor‐Oyer, Layton
• Format: Article
• Language: English
• Subjects: Body Mass Index; Calendars; Cardiorespiratory Fitness; Child; children; Children & youth; Childrens health; Exercise; Growth models; Humans; Obesity; Pediatrics; policy; Recreation; Schools
• ISSN: 2047-6302; 2047-6310
• DOI: 10.1111/ijpo.12789

Summary 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.