Invited Commentary: Cassel's "The Contribution of the Social Environment to Host Resistance"-A Modern Classic.

John Cassel's 1976 paper "The Contribution of the Social Environment to Host Resistance" (Am J Epidemiol. 1976;104(2):107-123) is widely regarded as a classic in epidemiology. He makes the compelling argument that the quality of a person's social relationships, that is, the degree to which her relationships are more stressful than supportive (or vice versa) influences her susceptibility to disease independent of genetic endowment, diet, physical activity, etc. Cassel's provocative thesis was anchored in a cogent synthesis of findings from animal experiments and observational studies on diverse human populations. Beginning in the late 1970s, the paper stimulated an explosion of epidemiologic research on social support and human health. Beyond advancing epidemiologic theory, Cassel showed how findings from various epidemiologic study designs could be marshalled to build a persuasive causal argument that impaired social bonds increase the risk of premature disease and death. The paper also foreshadowed core ideas of later theoretical constructs, such as weathering and allostatic load, regarding the power of chronic environmental stressors to accelerate biological aging across multiple organ systems. Cassel's assessment of the research and practice implications of his conclusions has remarkable contemporary resonance for the field of epidemiology.