A-35 Free Communication/Poster - Epidemiology - Disease Prevention/Treament - Youth: JUNE 1, 2011 7:30 AM - 12:30 PM: ROOM: Hall B
The role of physical activity in the development adolescent obesity is uncertain as the evidence has come mainly from cross sectional studies and studies with self-report measures.
PURPOSE: To examine the prospective associations between physical activity and fat mass in a contemporary cohort of adolescents.
METHODS: Physical activity, by accelerometry, and fat mass, by DXA, were measured at ages 12, 14 and 16 in the Avon Longitudinal Study of Parents and Children. The outcome was fat mass and the exposure was minutes/day of moderate to vigorous physical activity (MVPA). The trajectories of these variables across the three time points were modelled using a separate multilevel model for each variable. Fat mass was adjusted for height, height squared and age, while MVPA was adjusted for accelerometer wear time. Residuals from the multilevel models were regressed on one another to give estimates of the prospective associations between MVPA and fat mass. Missing residuals for MVPA, fat mass and confounders were imputed using multivariate imputation by chained equations. Models were adjusted for maternal education, smoking during pregnancy and pre-pregnancy obesity. Boys and girls were modelled separately.
RESULTS: Overall, 3373 girls and 3066 boys provided accelerometer data and DXA data on at least one occasion. An additional 15 mins/day of MVPA at age 12 was associated with 14.2% (95% CI 11.6%, 16.6%) lower fat mass at age 16 for boys and 7.5% (95% CI 5.1%, 9.8%) for girls. A 15 mins/day greater change in MVPA between ages 12 and 16 was associated with a change in fat mass between these two ages that was 5.2% (95% CI 2.6%, 7.7%) lower for boys and 6.3% (95% CI 4.3%, 8.2%) lower for girls. Each additional 5% fat mass at age 12 was associated with 0.14 (95% CI 0.04, 0.24) and 0.01 (95% CI -0.06, 0.05) fewer minutes of MVPA at age 16 in boys and girls, respectively.
CONCLUSIONS: We have shown a strong, negative association between MVPA at age 12 and fat mass at age 16. This association was stronger in boys than girls, with some evidence of the gender difference increasing over time when compared to previous analyses in this cohort with two time points analysed. Conversely, the association between change in MVPA and change in fat mass was stronger in girls than boys. There was little evidence to suggest an association between fat mass and later MVPA.