Associations of accelerometer measured school‑ and non‑school based physical activity and sedentary time with body mass index: IPEN Adolescent study

Background: This study examined the strength, shape and direction of associations of accelerometer-assessed overall, school- and non-school-based moderate-to-vigorous physical activity (MVPA) and sedentary time (ST) with BMI among adolescents across the world. Second, we examined whether these associations differed by study site and sex. Methods: Cross-sectional data from the IPEN Adolescent study, an observational multi-country study, were used. Participants wore an accelerometer for seven days, reported height and weight, and completed a socio-demographic survey. In total, 4852 adolescents (46.6% boys), aged 11–19 years (mean age = 14.6, SD = 1.7 years) were included in the analyses, using generalized additive mixed models. Results: Adolescents accumulated on average 41.3 (SD = 22.6) min/day of MVPA and 531.8 (SD = 81.1) min/day of ST, and the prevalence of overweight and obesity was 17.2% (IOTF), but these mean values differed by country. Linear negative associations of accelerometer-based MVPA and ST with standardized BMI scores and the likelihood of being overweight/obese were found. School-based ST and non-school-based MVPA were more strongly negatively associated to the outcomes than non-school based ST and school-based MVPA. Study site moderated the associations; adolescent sex did not. No curvilinear associations were found. Conclusions: This multi-country study confirmed the importance of MVPA as a potential protective factor against overweight/obesity in adolescents. Non-school-based MVPA seemed to be the main driver of these associations. Unexpected results were found for ST, calling for further examination in methodologically sound international studies but using inclinometers or pressure sensors to provide more precise ST measures.United States Department of Health & Human ServicesNational Institutes of Health (NIH) - USA R01 HL111378 FWO FWO12/ASP/102Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPQ) 306836/2011-4Grant Agency of the Czech Republic GA14-26896S GA17-24378SUniversity of Southern DenmarkHealth and Medical Research Fund (Food and Health Bureau, Government of the Hong Kong SAR, PR of China) 10111501Madras Diabetes Research Foundation (MDRF), ChennaiIsrael Science Foundation 916/12Universiti Sains Malaysia International Research Collaboration GrantHealth Research Council of New Zealand HRC12/329Portuguese Foundation for Science and TechnologyCenter for Forestry Research & Experimentation (CIEF) GV-2013-087United States Department of Health & Human ServicesNational Institutes of Health (NIH) - USA R01 HL083454Future Leader Fellowship from the National Health Foundation of Australia ID100046Australian Research Council FT140100085National Health and Medical Research Council (NHMRC) of Australia APP 1176885United States Department of Health & Human ServicesNational Institutes of Health (NIH) - USA R01 HL11137