It is widely recognized that social relationships and affiliations have powerful effects on physical and mental health. Although many social scientists from Emile Durkheim on have written about the critical role of social relationships in health outcomes, it was not until the 1970s that epidemiologists turned their attention to this issue.
In the first of these studies, in Alameda County, California (Berkman et al., 1979), men and women who lacked ties to others were 1.9 to 3.1 times more likely to die than those who had many contacts. A 1982 study in Tecumseh, Michigan (House et al., 1982), showed a similar association for men, but not for women, between social connectedness and participation and mortality risk. In the same year, D. Blazer reported similar results from a sample of elderly men and women in Durham County, North Carolina.
Schoenbach et al. (1986), in a study in Evans County, Georgia, used a measure of contacts modified from the Alameda County study and found risks to be significant in older white men and women even when controlling for risk factors, although some racial and gender differences were observed. In Sweden, the Goteborg study (Welin et al., 1985) showed that, in different cohorts of men, social isolation proved to be a risk factor for dying, independent of biomedical risk factors. A 1987 report by Orth-Gomér and Johnson reported significantly increased risks for men and women who have been socially isolated. Finally, in a study of men and women in eastern Finland, Kaplan and associates (1988) demonstrated that an index of social connections predicts mortality risk for men but not for women, independent of cardiovascular risk factors.
Several more recent studies, including the Established Populations for the Epidemiologic Study of the Elderly (EPESE) studies, confirm the continued importance of social relationships into late life. Furthermore, studies of large cohorts of men and women in a large health maintenance organization (Vogt et al., 1992) and male health professionals (Kawachi et al., 1996) suggest that social networks are, in general, more strongly related to mortality than to the incidence of disease. Studies in Danish men (Pennix et al., 1997) and Japanese men and women (Sugisawa et al., 1994) also indicate that social isolation and social support are related to mortality. Social networks and support have been found to predict a broad array of health outcomes, from survival after heart attacks to disease progression, functioning, and the onset and course of infectious diseases.
UPSTREAM AND DOWNSTREAM APPROACHES
Conceptually, social networks are embedded in a macrosocial environment in which large-scale social forces may influence network structure, which in turn influences a cascading causal process. Serious consideration of the larger macrosocial context in which networks form and are sustained is almost completely absent, and such consideration is needed in studies of social network influences on health.
Networks may operate through at least five primary pathways: (1) provision of social support, (2) social influence, (3) social engagement, (4) person-to-person contact, and (5) access to resources and material goods. These psychosocial and behavioral processes may influence even more proximate pathways to health status, including direct physiological stress responses, psychological states and traits, health-damaging or healthpromoting behaviors such as tobacco consumption or physical activity, and exposure to infectious disease agents.
Most obviously, the structure of network ties influences health via the provision of social support. This framework immediately acknowledges that not all ties are supportive. Social support is typically divided into subtypes, including emotional, instrumental, appraisal, and informational support.
Perhaps even more important than social support are the ways in which social relationships provide a basis for intimacy and attachment. Intimacy and attachment have meaning not only for relationships that traditionally are thought of as intimate (e.g., between partners, between parents and children) but for more extended ties. For instance, when relationships are solid at a community level, individuals feel strong bonds and attachment to places (e.g., a neighborhood) and organizations (e.g., voluntary and religious organizations).
Social networks may also influence health via social influence. Shared norms about health behaviors (e.g., alcohol and cigarette consumption, treatment adherence) might be powerful sources of social influence with direct consequences for the behaviors of network members.
A third, and more difficult to define, pathway by which networks may influence health status is by promoting social participation and social engagement. Getting together with friends, attending social functions, group recreation, and church attendance are all instances of social engagement. Several studies suggest that social engagement is critical in maintaining cognitive ability (Bassuk et al., 1999) and reducing mortality (Glass et al., 2000).
Another pathway by which networks influence disease is by restricting or promoting exposure to infectious disease agents through person-to-person contact. What is perhaps most remarkable is that the same network characteristics that can be healthpromoting can at the same time be health-damaging if they serve as vectors for the spread of infectious disease.
Little research has sought to examine differential access to material goods, resources, and services as a mechanism through which social networks might operate. This is unfortunate, given the existing work showing that social networks operate by regulating an individual's access to life opportunities by virtue of the extent to which networks overlap with other networks. In this way, networks operate to provide access, or to restrict opportunities, in much the same way that social status does.
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