Location: Children's Nutrition Research CenterTitle: Physical activity and metabolic risk among US youth: Mediation by obesity [abstract] Author
Submitted to: Pediatric Academic Society
Publication Type: Abstract Only
Publication Acceptance Date: 2/11/2011
Publication Date: 4/1/2011
Citation: Mendoza, J.A., Liu, Y., Stuff, J., Baranowski, T., Nicklas, T.A. 2011. Physical activity and metabolic risk among US youth: Mediation by obesity [abstract]. In: Program Guide of the Pediatric Academic Societies and Asian Society for Pediatric Research 2011 Joint Meeting, April 30-May 3, 2011, Denver, Colorado. p. 221. Interpretive Summary:
Technical Abstract: Physical activity has been inversely associated with metabolic risk, although pediatric studies are limited. It has been hypothesized that obesity mediates this relationship. Some studies reported that waist circumference (WC) is more highly related to metabolic risk than BMI, and may be a better mediator. The objective of this study was to examine whether obesity mediated the relationship between moderate-to-vigorous physical activity (MVPA) and metabolic risk among a large sample of US youth. We hypothesized that obesity would mediate the relationship between MVPA and metabolic risk and compared to BMI z-score, WC would be a stronger mediator between MVPA and metabolic risk. We conducted cross-sectional analyses using multiple linear regression models on participants aged 6-19 years from the National Health and Nutrition Examination Survey, 2003-2006. The main independent variable (MVPA) was assessed objectively by accelerometry. The mediators (BMI z-score and WC) were measured using standardized techniques. The main dependent variable was the metabolic syndrome risk score, e.g. the sum of the z-scores for blood pressure, HDL, triglycerides, and fasting glucose. Other dependent variables included total cholesterol, LDL, C-reactive protein, glycohemoglobin, and fasting insulin. Covariates included age, gender, race/ethnicity, income, total dietary energy intake, alcohol intake, saturated fatty acid intake, and smoking status. The product-of-coefficients method was used to test for mediation. WC alone was a significant (Sobel p=0.028) mediator of the relationship between MVPA and the metabolic syndrome risk score (% mediated = 94.1%). WC also mediated the following individual metabolic risk factors: systolic blood pressure (31.4%), HDL (51.2%), glycohemoglobin (21.1%) and C-reactive protein (59.6%) (p<0.005). BMI z-score mediated systolic blood pressure (22.7%), HDL (29.1%), and C-reactive protein (67.1%) (p<0.005). WC appears to be a more important mediator of the relationship between children's MVPA and clustered metabolic risk than BMI z-score. However, both WC and BMI z-score partially mediated several individual markers of metabolic risk. Interventions should target improving MVPA and reducing central obesity to reduce children's metabolic risk.