Higher social capital is associated with improved mental and physical health and reduced risk of premature mortality. We explored the relationship between five measures of structural social capital and 1) intermediate health outcomes (elevated C-reactive protein, cholesterol, blood pressure, and serum fibrinogen) and 2) distal outcomes (cardiovascular and all cause mortality). We did so using the National Health and Nutrition Examination Survey III 1988-1994 linked to the National Death Index with mortality follow-up through 2006. We employed ordinary least squares regression for the intermediate outcomes, seemingly unrelated regression (SUR) to consider combined effects, and Cox proportionate hazards models for mortality outcomes. We then performed extensive sensitivity analyses, exploring the contribution of various variables and reverse causality. We find that our measures of social capital did not predict statistically significant changes in the laboratory biomarkers we study. Nevertheless, belonging to organizations or attending church >12 times per year were associated with reduced all cause mortality (hazard ratio [HR] = 0.81, 95% confidence interval [CI] = 0.70-0.93 and HR = 0.72, 95% CI = 0.60-0.86, respectively). In SUR analyses, however, combined laboratory values were significant for all measures of social capital we study with the exception of visits to neighbors. This suggests that some forms of structural social capital improve survival through small changes in multiple measures of biological risk factors rather than moderate or large changes in any one measure.
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