Age moderates the association between social integration and diurnal cortisol measures.

Social integration is defined as the degree to which an individual participates in a broad range of social relationships. Although measures of social integration vary across studies, it is often assessed as the number of social roles (e.g., parent, friend, student, volunteer) that an individual reports actively participating in. More socially integrated individuals tend to be healthier than those less socially integrated, but the biological mechanisms through which this occurs remain unclear. One possibility is that social integration might alter the function of the hypothalamic-pituitary-adrenal axis, of which cortisol is a key product, and in turn influence a broad range of health outcomes. This study examined the association between social integration and two indices of cortisol in a community sample of 680 healthy men and women aged 18-55. Because the social roles held by younger individuals may be more numerous yet superficial than those held by older individuals, this study also tested the hypothesis that these associations could be moderated by age such that lower levels of integration would be associated with cortisol dysregulation for older but not younger individuals in our sample. Participants provided salivary cortisol samples during waking hours on three days that were used to calculate diurnal cortisol levels and slopes. Increased social integration was associated with lower cortisol AUC among older (ages 35-55) but not younger (ages 18-34) individuals in our sample. Moreover, while increased social integration was associated with steeper diurnal cortisol slopes regardless of age, this association was strongest among older individuals. Differences in health behaviors, affect, and psychological stress did not mediate these associations. The results of this study support cortisol as a candidate biological mechanism through which increased social integration is associated with better physical health among older individuals.