ARS | Publication request: Physical activity as a mediator of the relationship between active commuting to school and adiposity

Submitted to: International Society for Behavioral Nutrition and Physical Activity
Publication Type: Abstract Only
Publication Acceptance Date: March 1, 2009
Publication Date: June 1, 2009
Citation: Watson, K., Mendoza, J., Nguyen, N., Cerin, E., Baranowski, T., Nicklas, T. 2009. Physical activity as a mediator of the relationship between active commuting to school and adiposity [abstract]. In: The International Society for Behavioral Nutrition and Physical Activity Abstract Book, June 17-20, 2009, Lisbon, Portugal. p. 327.

Technical Abstract: Active commuting to school (ACS) has been associated with more moderate-to vigorous physical activity (MVPA) and decreased adiposity among youth. However, no studies have examined if MVPA mediates the relationship between ACS and adiposity. We hypothesized that ACS would be inversely associated with adiposity and that MVPA would mediate that relationship. Cross-sectional survey analysis using multiple linear regression models on a nationally representative sample of participants aged 12-19 years from the National Health and Nutrition Examination Survey, 2003-2004 (n=789 unweighted). The main exposure variables, ACS, were assessed by participant recall. BMI z-score, waist circumference, and skin folds were obtained using standardized techniques. MVPA was objectively measured by accelerometers. Covariates included age, gender, race/ethnicity, poverty-to-income ratio, and dietary energy intake. The product-of-coefficients method was used to test for mediation. In multivariate models, ACS was inversely associated with skin folds (std. beta=-0.06, p=0.029, R**2=0.12), BMI z-score (std. beta=-0.07, p=0.046, R**2=0.05), and waist circumference (std. beta -0.06, p=0.093, R**2=0.08). ACS was positively associated with overall daily MVPA (std. beta=0.12, p=0.024, R**2=0.31) and with before- and after-school MVPA (std. beta=0.20, p<0.001, R**2=0.20). Before- and after-school MVPA mediated the relationship between ACS and waist circumference (Sobel p=0.048), skin folds (Sobel p=0.070), and BMI-z score (Sobel p=0.093). Greater ACS among US youth was associated with indicators of lower adiposity. Greater ACS contributed to greater before- and after-school MVPA, which in turn, contributed to lower adiposity. This mediation relationship was most apparent for central obesity and warrants further study.