Background Although several studies have reported rather consistent associations between socioeconomic status (SES) and allostatic load (AL), so far no study has examined the influence of SES over the life course on AL. The aim of the present study was to investigate the association between SES over the life course and AL in mid-adulthood, guided by the conceptual models of cumulative risk, critical period and social chain of risk.

Methods The sample comprises a 27-year prospective cohort (n=1071) from northern Sweden. Participants (n=855, 79.8%) completed questionnaires at the ages of 16, 21, 30 and 43 years. A health examination was performed at age 43 years after an overnight fast, including physical examination and blood sampling, and participants completed 1-day salivary cortisol sampling (four samples). SES was based on parental occupation at age 16 years and participants' own occupation at ages 21, 30 and 43 years. Information on daily smoking, snuff use, high alcohol consumption and physical inactivity was reported by the participants. An AL index was constructed from tertiles of 12 biological parameters.

Results Cumulative socioeconomic disadvantage was related to AL in both women and men. The association was largely explained by health behaviours in men, but was independent of health behaviours in women. In women, an association was observed between AL and SES in adolescence, whereas in men only current SES was related to AL, independently of current health behaviours.

Conclusions SES over the life course influences the level of multi-systemic dysregulation in mid-adulthood, with the strongest support for the cumulative risk model.