Objectively Measured Sedentary Behavior is Associated With Body Mass Index, Independently of Physical Activity Levels, in School-Aged Portuguese Youth

Aim Some studies have analyzed the relation between sedentary behavior (SB) and body composition in children and adolescents. However most of the studies have used self-reported measures of SB and/or did not consider the potential confounding effect of physical activity in their analysis. The aim of this study was to analyze the association between objectively measured SB and body mass index (BMI) in 2 506 Portuguese children and adolescents of both genders aged 10 to 18 years, accounting for physical activity levels.

Methods Physical activity and SB were assessed with accelerometry. Weight and height were measured with standardized protocols and BMI was calculated. Z-Scores by age and gender were constructed for BMI. Linear regression models were performed to analyze the relationship between SB and BMI.

Results Linear regression analysis showed that percentage of time spent in SB was positively associated with BMI Z-Scores (β=0.06; 95%CI: 0.001-0.010; p=0.008), after adjustments for age, gender, moderate-to-vigorous physical activity and accelerometer wear time.

Conclusions These findings suggest that PA levels may not overcome the deleterious association of sedentary time on BMI. Our data stress the importance of promoting physical activity and discouraging sedentary behavior in children and adolescents aged 10 to 1.8 years.