networks and the resources that flow through them to behaviors related to tobacco and alcohol consumption, physical activity, dietary patterns, and sexual behaviors. By establishing and enforcing normative behaviors, networks may influence work- and school-related behaviors, criminal behaviors, and other social behaviors. Networks may also influence patterns of self-esteem, efficacy, competence, and other conditions leading to mental health outcomes. Finally, increasing evidence suggests that social networks and related functions impact physiological processes directly by several pathways. Invoked most frequently is a stress pathway linked to neuroendocrine regulation, inflammation, and immune function (Gruenewald et al., 2009; Loucks et al., 2006a, 2006b; Uchino, 2006). Berkman (1988) hypothesizes that social isolation or the negative aspects of social ties influence health by accelerating the rate of aging. Social isolation, conflict, or lack of support may be viewed as a chronically stressful condition to which the organism responds by aging more rapidly. This acceleration would be especially evident in cardiometabolic functions that decline with age.

Social Networks and Mortality

Numerous studies from many industrialized countries in North America, Europe, and Asia have shown that aspects of social networks or social support are related to mortality, including mortality from all causes combined (Berkman et al., 2004; Blazer, 1982; Eng et al., 2002; Fuhrer and Stansfeld, 2002; Kaplan et al., 1988; Khang and Kim, 2005; Orth-Gomer and Johnson, 1987; Orth-Gomer et al., 1993, 1998; Penninx et al., 1998; Pinquart and Duberstein, 2010; Pinquart and Frohlich, 2009; Seeman, 1996; Sugisawa et al., 1994). Although all of these studies are longitudinal in the sense of including a mortality follow-up after baseline assessment of social networks, they vary widely in their ability to control for important covariates or to disentangle the extent to which such covariates are mediators along the pathway from social networks to increased mortality risk. Furthermore, networks themselves develop in the context of individual exposures over a life course, some of which may be related to health.

Focusing on some of the more salient aspects of the above-mentioned mortality studies helps identify areas for further work. For instance, it appears that different aspects of social networks may be more important at different ages, or for men or women, or in different countries. In a followup to the original Alameda study (Berkman and Syme, 1979), Seeman and colleagues (1987) report that over a 17-year period, the subjects with stronger social networks and community ties were significantly less likely to die. The types of social ties with the greatest effect on mortality differed by age. For adults 60 and younger, marital status had the greatest association with the risk of dying, while for those over 60, the most meaningful



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