Background The relationship between socioeconomic status and mortality has been well established; however, the extent to which biological factors mediate this relationship is less clear, and empirical evidence from non-Western settings is limited. Allostasis, a cumulative measure of physiological dysregulation, has been proposed as the underlying mechanism linking socioeconomic status to adverse health outcomes. The current study aimed to ascertain the contribution of allostatic load (AL) and health behaviours to socioeconomic inequalities in mortality among Korean adults.

Methods The sample comprised 70 713 middle-aged and older-aged adults, aged 40–79 years from the Korean Metabolic Syndrome Mortality Study. Using structural equation modelling (SEM), mediation analyses were performed to estimate the effects of socioeconomic position (SEP) on mortality over the follow-up and the extent to which AL, physical exercise and non-smoking status mediate the association between SEP and mortality.

Results A total of 5618 deaths (7.9%) occurred during the mean follow-up of 15.2 years (SD 2.9). SEM confirmed a direct significant effect of SEP on mortality, as well as significant indirect paths through AL, physical exercise and non-smoking status.

Conclusions Our findings provide support for the mediating role of AL and health behaviours in the link between SEP and mortality. Policies designed to reduce social disparities in mortality in the long term should primarily focus on reducing stress and promoting healthy lifestyles among the socially disadvantaged groups. Future studies should further assess the role of other mediators such as psychosocial factors, which may contribute to socioeconomic inequalities in mortality.