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This study evaluates whether school start times influence sleep patterns and obesity in adolescents.

June 19, 2026Open Access

Is School Schedule a Risk Factor for Obesity in Adolescents?

LGLM GoesUniversidade Tecnológica Federal do Paraná DMD MoserUniversidade Tecnológica Federal do Paraná AKAC KappUniversidade Tecnológica Federal do Paraná

Key Points

This study evaluates whether school start times influence sleep patterns and obesity in adolescents.
68 students aged 12-16 years from two public schools participated, 37 attended morning and 31 afternoon schedules.
Participants completed questionnaires regarding sleep habits, and measurements of waist circumference, height, and weight were taken.
Afternoon shift students had later sleep times and longer sleep duration than morning shift students.
No significant differences in body mass index (BMI) and waist circumference (WC) between the two groups.

Abstract

*Correspondence author e-mail; florliz goes@hotmail.com Introduction: Adolescents show a sleep phase delay. In contrast, schools from 5th grade often anticipates school starting times. As a result, there is a partial sleep deprivation, which has been associated with an increase in body mass index. One could suppose that morning school schedule might be a risk factor for obesity in adolescents. The aim of this study is to compare sleep-wake patterns, body mass index (BMI) and waist circumference (WC) of adolescents submitted to two school schedules, morning and afternoon. Methods: 68 students (29 boys and 39 girls) from two public schools in Curitiba (PR), aged from 12 to 16 years, participated in the study. 31 students attended afternoon schedules (1:00pm to 5:30pm) and 37 morning schedules (7:20am to 11:45am). They filled out a questionnaire about their sleep habits. Waist circumference (WC), height and weight were measured and body mass index (BMI) was calculated. Results: Sleep variables, BMI and WC were compared using the Kruskal-Wallis test, considering school schedule, morning or afternoon, the independent variable. Table 1 shows the results. Afternoon shift students showed later sleep times and had longer sleep duration when compared with morning shift students, although there were no differences in BMI and WC. Conclusion: The results confirm the role of school times in the partial sleep deprivation which adolescent attending earlier school starting times are submitted. The hyphotesis that school schedules are involved in body mass index gain was not confirmed. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil

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