Which contributes more to childhood adiposity-high levels of sedentarism or low levels of moderate-through-vigorous physical activity? The Iowa bone development study

Objective To examine the relative importance of sedentarism and moderate-to-vigorous physical activity for adiposity development in children and adolescents. Study design A total of 277 boys and 277 girls (95% white; two-thirds of parents with college graduation or higher education) from the Iowa Bone Development Cohort Study completed body fat and accelerometry measurement at examinations of 8, 11, 13, and/or 15 years of age (during 2000-2009). The main exposure was accelerometrymeasured sedentary time, frequency of breaks in sedentary time, and moderate- to vigorous-intensity physical activity time. The outcome was dual energy x-ray absorptiometry-measured body fat mass. Results Adjusted for age, height, physical maturity, and sedentary time, growth models showed that high moderate-to-vigorous physical activity time was associated with low body fat mass in both boys (coefficient b = - 0.10 ± 0.02) and girls (b = - 0.05 ± 0.01; P < .01). However, sedentary time and frequency of breaks in sedentary time were not associated with body fat mass. Conclusions This study does not support an independent effect of sedentarism on adiposity. The preventive effect of moderate- to vigorous-intensity physical activity on adiposity in children and adolescents remained strong after adjusting for the effect of sedentarism.