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The influence of social relationships on aging and the development of cardiovascular disease--a review.

As little as ten years ago, there was virtually no information on the relationship of social networks or social isolation to mortality risk. In 1976, John Cassel in a widely cited paper on the contribution ofthe social environment to host resistance summarized information on disease risks associated with diverse social phenomena ranging from social disorganization to acculturation and psychosocial resources. He concluded that epidemiologists needed to recognize the importance of the social support provided to individuals by the primary groups of importance to them. This paper, coupled with several other seminal papers in the field (Antonovsky, 1972; Syme, 1974, Hinkle, 1973), led to the direct examination of social networks, social support, isolation, and social integration and their association with mortality risk. Now, almost ten years later, after this call for action, where do we stand? With regard to the association between social networks and coronary heart disease (CHD) morbidity, the amount of evidence is still not impressive. However, the association between social ties and mortality risk from all causes has been explored in at least seven large epidemiological studies including one focusing on mortality risk among men who have had at least one myocardial infarction (Berkman & Syme, 1979; House et al., 1982; Blazer, 1982; Schoenbach et al., 1985; Welin et al., 1985; Reed et al., 1983; Rubberman et al., 1984). Of the seven mortality studies published to date, social isolation or lack of support is consistently associated with increased mortality risk among white men. There are only three studies in which risks among men and women can be compared (Alameda County, Evans County and Tecumseh) and of these, only in Alameda County is social isolation associated with increased mortality risks for women. Three studies have explored social ties and mortality risks in nonwhite groups (e.g. blacks in Alameda and Evans County studies and Japanese-Americans in Hawaii). All three studies show markedly weaker effects among non-whites. The studies published to date have been thoughtprovoking and stimulating. Most importantly, when added to the studies on bereavement and marital status (Chandra et al., 1983; Parkes et al., 1969; Helsing et al., 1981; Carter et al., 1970), they convince us that something about human relationships influences physical health and especially longevity. However, we do not know (1) how they influence health or which relationships or what aspects of relationships are important or detrimental to well-being and (2) why they seem to carry greater mortality risks for some groups ofpeople than others (e.g. men versus women). It is these two questions that guide our comments. Social conditions and specifically social networks and support may lead to disease by altering known biological risk factors (e.g. blood pressure or serum cholesterol), health behaviour (e.g. cigarette smoking, alcohol consumption, or dietary practices), or they may have their impact on risk by altering some, as yet unidentified, physiological processes. Since most studies show a modest reduction in risk when controlling for biomedical risk factors, primarily risk factors for CHD, networks may influence mortality, in part, via these pathways. However, since the correlations between networks, support and these biomedical factors are small, and in some studies non-significant, it is equally clear that other pathways must be in place. We would like to propose something controversial for which there is little evidence at the present time that social networks and support influence health status and longevity by influencing what longevity is most obviously related to the rate of aging of the organism. Following this line of reasoning one would hypothesize that social isolation or lack ofsupport is a chronically stressful situation to which the organism responds by aging faster. What are the physiological alterations associated with aging that are capable of causing such fatal consequences? Certainly, the de-