January 25, 2018
3 min read

Obesity may involve ‘social contagion’ component

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Parents and children are more likely to have overweight or obesity if they live in a county with a higher rate of obesity, according to findings published in JAMA Pediatrics.

“Disentangling the extent to which the clustering of obesity within networks is due to social contagion vs. the competing explanations of self-selection (ie, homophily and residential selection) and shared environment is crucial because of their different implications for public health policy-making,” Ashlesha Datar, PhD, of the Center for Economic and Social Research at the University of Southern California, and Nancy Nicosia, PhD, of the RAND Corporation in Boston, wrote in the study background. “A contagion effect would favor policies that target social networks, such as directing interventions toward well-connected individuals within networks to leverage their potential multiplier effect or interventions that seek to change norms and attitudes. A shared environment effect would favor interventions that target aspects of the built or policy environment. However, self-selection would suggest a more limited role for interventions focusing on social networks or built environments.”

The researchers analyzed data from 1,314 adults and 1,111 children participating in the Military Teenagers’ Environments, Exercise and Nutrition (M-TEEN) study, which recruited families of U.S. Army personnel located at 12 military installations from 35 counties across the United States (40% white; 22% black; 25% Hispanic; 44% lived on the installation). Families with a child aged 12 or 13 years were recruited between March 2013 and December 2014. Researchers assessed child height and weight via self-report and parent-report, and a subsample of children attended installation visits on specified days in which height and weight were measured (n = 458). Obesity exposure was measured using the adult obesity rate in the service member’s assigned county; county obesity rates were obtained from 2013-2014 Robert Wood Johnson Foundation County Health Rankings data. Researchers estimated the association between the military installation’s county obesity rate and body weight outcomes of children and parents using linear and logistic regression analyses. Additionally, researchers tested for evidence of “self-selection” by examining unadjusted models, by comparing the characteristics of families in counties with high vs. low obesity rates and through a falsification test, estimating the association between county obesity rate and both child and parent height.

Within the cohort, 75% of parents had overweight or obesity; overweight and obesity among children ranged from 25% from parent-reported figures to 28% from anthropometric measures. County obesity rates ranged from 21% (El Paso County, Colorado) to 38% (Vernon County, Louisiana). Most families (63%) had lived at their current installation for at least 2 years.

The researchers found that military families living in counties with a higher obesity rate had a higher BMI and were more likely to have overweight or obesity vs. military families living in counties with a lower obesity rate. Every 1 percentage point higher county obesity rate was associated with a 0.08 kg/m² higher BMI among parents (95% CI, 0.02-0.13) and 5% higher odds for obesity (adjusted OR = 1.05; 95% CI, 1.02-1.08). Additionally, every 1 percentage point higher county obesity rate was associated with 4% higher odds for overweight and obesity (aOR = 1.04; 95% CI, 1.01-1.06).

The associations persisted in both adjusted and unadjusted models, according to researchers, and there were no observed systematic differences in family characteristics by county obesity rate. A falsification test showed no association between child or parent height and county obesity rate.

“The natural experiment design of this study, whereby military families are exogenously assigned to different installations (and hence different counties) in the course of their service allowed us to address concerns about self-selection, which is one of the primary limitations of existing studies,” the researchers wrote. “We found no systematic pattern in the observed characteristics of families at installations located in counties with higher vs. lower obesity rates that could explain our findings.”

In commentary accompanying the study, Leonard H. Epstein, PhD, and Xiaozhong Wen, MD, PhD, both of the Jacobs School of Medicine and Biomedical Sciences at the University of Buffalo in New York, wrote that the idea of obesity being “contagious” provides a useful analogy for pediatricians to recognize the association of the social environment with obesity through social networks and social norms.

“It provides a stimulus to action to learn how to deactivate the ‘virus,’ preventing transmission to future generations,” Epstein and Wen wrote. – by Regina Schaffer

Disclosures: Epstein reports he has served as a consultant for Kurbo and owns an equity stake in the company. The other authors report no relevant financial disclosures.