Collective efficacy and obesity: the potential influence of social factors on health.

Social determinants have been identified as a fundamental cause of health and disease in most industrialized countries. However, much less is known about which characteristics of communities may lead to disparities in health outcomes. Collective efficacy--the willingness of community members to look out for each other and intervene when trouble arises--is a social factor shown to be associated with outcomes related to obesity, including premature mortality and cardiovascular disease. The objective of this study is to determine whether neighborhood collective efficacy is associated with individual measures of body mass index (BMI) in adolescents. We use a multi-level, cross-sectional survey in Los Angeles County, involving 807 adolescents in 684 households in 65 neighborhoods in addition to a sample of 3000 adult respondents. The main outcomes measures are BMI, at risk of overweight, and overweight status. Using a two-level model, we find significant relationships between collective efficacy and all three outcomes, net of levels of neighborhood disadvantage. The associations between BMI and collective efficacy could potentially be explained by several factors, including a metabolic pathway, neighborhood differences in the physical and social environments, or a combination of these two. If group-level collective efficacy is indeed important in the regulation of individual-level net energy balance, it suggests that future interventions to control weight by addressing the social environment at the community level may be promising.