Screen time, adiposity and cardiometabolic markers: mediation by physical activity, not snacking, among 11-year-old children

Abstract

Background:There is evidence for a relation of TV viewing with adiposity and increased cardiometabolic risk factors in children and adolescents. It is unclear to what extent this relation is mediated by snacking and lack of physical activity. We determined whether associations of screen time with adiposity and cardiometabolic markers were mediated by these behaviours.Methods:Children from a population-representative Dutch birth cohort (n=1447) reported screen time and other lifestyle factors by a questionnaire around the age of 11 years (range 10-14) and had anthropometry and cardiometabolic markers measured around the age of 12 years (range 12-14). Adjusted associations of screen time with snacking, physical activity, adiposity and cardiometabolic markers (total-to-high-density lipoprotein cholesterol (TC/HDLC) ratio, blood pressure, glycated haemoglobin) were assessed by using formal mediation analysis. We tested the hypothesized paths by structural equation modeling, which allows quantification of the indirect effects associated with potential mediators.Results:Children with ≥20 h screen time per week consumed more snacks (1.9 vs 1.3 portions per day) and were less physically active (4.3 vs 4.8 days per week) than children with maximum 6 h screen time. Screen time was directly associated with higher adiposity (standardized β=0.10-0.12 depending on the outcome, P<0.001), and indirectly through less physical activity. The association of screen time with TC/HDLC ratio was almost completely mediated by adiposity (β=0.39, P<0.0001), and to a minor extent by physical activity (β=-0.06, P=0.02). There was no direct association of screen time with TC/HDLC ratio.Conclusions:The adverse association of screen time with adiposity was partly mediated by physical activity, but not by snacking. The association of screen time with TC/HDLC ratio was almost completely mediated by adiposity. Our results may suggest that future efforts in society and public health should be directed to replace screen time with physical activity for reducing children's adiposity and cardiometabolic risk.International Journal of Obesity advance online publication, 22 July 2014; doi:10.1038/ijo.2014.110.