Social capital and health: a study of adult twins in the U.S.

BACKGROUND A growing number of studies have suggested a link between social capital and health. However, the association may reflect confounding by factors, such as personality or early childhood environment, that are unmeasured prior common causes of both social capital and health outcomes. The purpose of this study was to investigate the impact of social capital on physical and mental health among adult twins in the U.S. METHODS A cross-sectional national survey of twins within the National Survey of Midlife Development in the U.S. (MIDUS), 1995--1996 was analyzed in 2007. The study population included 944 twin pairs (37.2% monozygotic [MZ] and 62.8% dizygotic [DZ]). Data were obtained on individual-level social capital variables (social trust, sense of belonging, volunteer activity, and community participation); health outcomes (perceived physical and mental health, depressive symptoms and major depression); and individual covariates (age, gender, race, education, working status, and marital status). A fixed-effects model was used to examine health status among twin pairs who were discordant on levels of social capital. RESULTS In the individual data analysis, social trust, sense of belonging, and community participation were each significantly associated with health outcomes. In the fixed-effects model, physical health remained significantly positively associated with social trust among MZ and DZ twins. However, major depression was not associated with social capital. CONCLUSIONS The present study is the first to find the independent positive effect of social trust on self-rated physical health using fixed-effects models of twin data. The results suggest that the association between social capital and physical health status is not explained by unobserved confounds, such as personality or early childhood environment.