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Social contagion refers to the spreading of a behaviour, idea, attitude, or even an emotion, across a social group due to imitation and conformity by its members. The idea that obesity may spread due to social contagion is based on its observed clustering across networks of individuals, who are joined by other types of social similarities (e.g. friendships and residences). However, previous analyses were based on observational data and are prone to confounding and self-selection into social networks. This study took a unique approach, leveraging the natural experiment of military assignment, which except in rare cases is beyond the control of the individual. The findings show that families who are assigned to US counties with higher rates of obesity are more likely to be overweight or obese. The effects strengthened with longer duration of residence. The findings were not explained by differences in the built environment that might influence outdoor physical activity. In our efforts to control overweight and obesity, we need to understand and tackle the 'social norms' held by populations and population subgroups, which can often foster unhealthy attitudes, beliefs and behaviours towards food, exercise, and weight status, even from very early ages (1).
Datar et al. (Tue,) studied this question.