Time-varying Effects of Screen Media Exposure in the Relationship Between Socioeconomic Background and Childhood Obesity

We investigated to what extent social inequalities in childhood obesity could be reduced by eliminating differences in screen media exposure. METHODS: We used longitudinal data from the UK-wide Millennium Cohort Study (n = 11,413). The study measured mother’s educational level at child’s age 5. We calculated screen media exposure as a combination of television viewing and computer use at ages 7 and 11. We derived obesity at age 14 from anthropometric measures. We estimated a counterfactual disparity measure of the unmediated association between mother’s education and obesity by fitting an inverse probability-weighted marginal structural model, adjusting for mediator–outcome confounders. RESULTS: Compared with children of mothers with a university degree, children of mothers with education to age 16 were 1.9 (95% confidence interval [CI] = 1.5, 2.3) times as likely to be obese. Those whose mothers had no qualifications were 2.0 (95% CI = 1.5, 2.5) times as likely to be obese. Compared with mothers with university qualifications, the estimated counterfactual disparity in obesity at age 14, if educational differences in screen media exposure at age 7 and 11 were eliminated, was 1.8 (95% CI = 1.4, 2.2) for mothers with education to age 16 and 1.8 (95% CI = 1.4, 2.4) for mothers with no qualifications on the risk ratio scale. Hence, relative inequalities in childhood obesity would reduce by 13% (95% CI = 1%, 26%) and 17% (95% CI = 1%, 33%). Estimated reductions on the risk difference scale (absolute inequalities) were of similar magnitude. CONCLUSIONS: Our findings are consistent with the hypothesis that social inequalities in screen media exposure contribute substantially to social inequalities in childhood obesity.