Psychologists, sociologists, and epidemiologists have contributed a great deal to our understanding of how social processes influence physiological processes that help to explain the link between social ties and health. For example, supportive interactions with others benefit immune, endocrine, and cardiovascular functions and reduce allostatic load, which reflects wear and tear on the body due, in part, to chronically overworked physiological systems engaged in stress responses (McEwen 1998; Seeman et al. 2002; Uchino 2004). These processes unfold over the entire life course, with effects on health. Emotionally supportive childhood environments promote healthy development of regulatory systems, including immune, metabolic, and autonomic nervous systems, as well as the hypothalamic-pituitary-adrenal (HPA) axis, with long-term consequences for adult health (Taylor, Repetti, and Seeman 1997). Social support in adulthood reduces physiological responses such as cardiovascular reactivity to both anticipated and existing stressors (Glynn, Christenfeld, and Gerin 1999). Indeed, continuously married adults experience a lower risk of cardiovascular disease compared with those who have experienced a marital loss, in part due to the psychosocial supports conferred by marriage (Zhang and Hayward 2006).
