Background: The present study aimed to analyse the effect of an intervention for increasing physical activity (PA) and reducing sedentary time on adolescents' total sleep time (TST) and to examine whether the effect on adolescents' TST was mediated by the intervention changes on screen-based sedentary time.
Methods: This study was a school-based cluster-randomized controlled trial conducted with Brazilian adolescents in Grades 7 to 9 (in 2017). Three schools participated in each of the intervention group (IG) and control group (CG). The intervention involved the following three strategies designed to increase PA and reduce sedentary time: (a) teacher training, (b) environmental improvements, and (c) health educational component. TST and screen-based sedentary time (television use, cell phone use, playing on computer/video game, and computer use that is not for gaming purposes) on weekdays and weekends were assessed using a standardized questionnaire. Generalized linear mixed models were conducted to verify the effect of the intervention on TST. Mediation analyses were used to examine the mediator role of changes in screen-based sedentary time in the relationship between the intervention and TST.
Results: Overall, 597 students participated in this study (mean age: 13.0 ± 1.0 years; IG: n = 351; CG: n = 246). The intervention had no effect on TST on weekdays and weekends. Adolescents in the IG were more likely to report ≤2 hr of television viewing per day on weekdays at follow-up. Mediated effects by screen media use were not significant.
Conclusions: The school-based intervention for increasing PA and reducing sedentary time had no effect on adolescents' TST.
Trial registration: ClinicalTrials.gov NCT02944318.
Keywords: adolescent; randomized controlled trial; school; sedentary behaviour; sleep; student.
© 2020 John Wiley & Sons Ltd.