The Association of Physical Activity with Obesity Development during Adolescence:
NHLBI Growth and Health Study (NGHS)
The longitudinal data from NGHS show that physical activity (PA) fell by 35% in daily and 83% in weekly levels during adolescence, with greater decline for black (B) than white (W) girls. During these 10 years, the prevalence of obesity in NGHS doubled with higher rates in B girls than in W. The aim of this report is to examine the longitudinal association of PA and obesity development in 1213 B and 1166 W NGHS girls with annual followup from ages 9-10 to 18-19 years. Activity was assessed with a 3-day diary (AD) in tandem with a food diary and a habitual (past year) activity questionnaire (HAQ). Obesity was defined as ≥85 th percentile of the sum of skinfolds (at triceps, subscapular and suprailiac sites) using age-specific cutpoints. Longitudinal analysis (GEE) was done with the likelihood (odds ratio, OR) of obesity as the outcome measure. Predictor variables included race, visit, age of menarche, average daily energy intake, and activity (as average daily activity, AD score, in one model and average weekly activity, HAQ score, in another). Visit (age) and race were significant predictors (1.51 OR for black race) of obesity. Age of menarche, energy intake, and HAQ scores were significantly (p<0.001 for all) and inversely associated with obesity. There was no significant interaction between race and HAQ, p=0.27. However, interaction between visit and HAQ was significant (p=0.01), indicating lower OR with higher HAQ from age 15 onward. The above analyses were repeated for AD in place of HAQ. Daily activity was not significantly (p=0.37) associated with obesity risk. We conclude that habitual, rather than short-term (AD), activity exerted a significant protective effect on the risk of developing obesity during adolescence. This finding is consistent with our previously reported lack of association between daily PA and obesity development in the NGHS cohort. Habitual PA during mid- to late adolescence seems to confer a greater protective effect on obesity risk. Our study confirms the role of PA in the marked increase in obesity prevalence during adolescence. Hence, obesity prevention needs to aim at fostering habitual activity, especially for black girls.