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

Joost Groeniger

Willem de Koster

Jeroen van der Waal

From the ^{Department of Public Health, Erasmus University Medical Centre Rotterdam, Rotterdam, The Netherlands}

^{Department of Public Administration and Sociology, Erasmus University Rotterdam, Rotterdam, The Netherlands.}

^{Corresponding author.}

Correspondence: Joost Oude Groeniger, Department of Public Health, Erasmus University Medical Centre, PO Box 2040, 3000 CA Rotterdam, The Netherlands. E-mail: ln.cmsumsare@regineorgeduo.j.

Received 2019 Sep 23; Accepted 2020 May 4.

This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal.

Background:

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.

Keywords: Causal mediation analysis, Childhood obesity, Health inequalities, Marginal structural model, Screen media exposure

Background:

The prevalence of excess weight among children has risen dramatically in the last 4 decades.¹,2 Childhood obesity is linked to a range of adverse outcomes across the life course, including greater risk of chronic diseases, more mental health problems, and lower socioeconomic attainment.³ Especially alarming is the differential distribution of childhood obesity across socioeconomic groups.⁴ Socioeconomically disadvantaged children are at a considerably higher risk to develop obesity, and recent evidence from the United Kingdom suggests that these inequalities will keep rising.⁴ Given the already disproportionate health disadvantage of children growing up in lower socioeconomic environments, and the need to intervene early in life to prevent obesity before it is established, tackling social inequalities in childhood obesity is listed as a vital public health strategy.⁵ Particularly for children, who have little control over the circumstances affecting their health, potentially avoidable health inequalities are considered unjust.⁶,7 Reducing these inequalities, however, requires evidence on the effect of intervening on modifiable mechanisms in the relationship between socioeconomic background and childhood obesity.

Screen media exposure is a major risk factor for childhood obesity and an increasingly common leisure activity of children.⁸–10 Many children spend hours per day behind television or computer screens, which substantially increases their obesity risk.¹¹ Screen media exposure may affect body weight by increasing food consumption and exposure to food and beverage advertisements, lowering energy expenditure, and reducing sleep duration.⁹,12 Moreover, screen media exposure is substantially higher among children from lower socioeconomic backgrounds than among children from higher socioeconomic backgrounds.¹³,14 Limited financial resources to engage in more expensive leisure activities are likely to be associated with increased screen media exposure among lower socioeconomic status families. Moreover, more disadvantageous neighborhood conditions may discourage playing outside.¹⁵ Differences in screen media habits may also result from other social determinants and transmit to children via socialization and social learning practices.¹⁶–19 First, norms in more-educated social environments have shifted to disapproval and stigmatization of sedentary activities, such as television, viewing in favor of a more active lifestyle.²⁰,21 Second, childrearing practices of more-educated parents are increasingly aimed at improving children’s development, resulting in more extracurricular activities and less screen media exposure.²² Third, greater cognitive abilities may result in a higher awareness of the negative health consequences of screen media exposure and a preference for other activities that require greater information processing capacities.²³

To examine to what extent screen media exposure contributes to social inequalities in childhood obesity, we used longitudinal data from the Millennium Cohort Study. We aimed to estimate to what extent social inequalities (measured by mother’s educational level) in childhood obesity at age 14 would be reduced if differences in screen media exposure (television viewing and computer use) at ages 7 and 11 were eliminated. To do so, we used mediation methods that are able to estimate the effect of time-varying mediators even in the presence of (time-varying) confounders that are also on the causal pathway from exposure to outcome.²⁴–27

Footnotes

The authors report no conflicts of interest.

Supplemental digital content is available through direct URL citations in the HTML and PDF versions of this article (www.epidem.com).

Replication of results: Due to data protection regulations, the data cannot be made available by the authors. Interested researchers may obtain the data via UK Data Archive. Annotated Stata code is provided in the eAppendix.

Footnotes

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