Explaining variations in allostatic load in later life: a longitudinal cohort study of socioeconomic life course mechanisms in Germany

Different life course models explain variations in allostatic load (AL) as the accumulation, sensitive period, path, and social mobility models. This study investigates which life course models are most instrumental in explaining AL in later life. Three waves of the longitudinal German Heinz Nixdorf Recall cohort study were used considering 11,959 observations of 4,814 individuals aged 45-75 years at baseline. AL was derived from 13 biomarkers and socioeconomic status (SES) was measured by life course and current SES. Random-effects linear regression models were employed to test for the sensitive period and path models. An interaction effect between life course and current SES was considered to test for the accumulation and social mobility models. The path model was tested by mediation modeling using the g-formula approach. Both life course and current SES were significantly and negatively associated with AL across all models, with current SES showing stronger effect. A significant positive interaction between the two SES measures supported the accumulation and social mobility models. Mediation analysis confirmed the path model, showing that current SES significantly mediated a substantial portion (49.0-73.4%) of the life course SES effect on AL, while the remaining direct effect offers partial support for the sensitive period model. The results indicate that the biological embedding of socioeconomic disadvantage is driven by the simultaneous operation of multiple life course mechanisms. Strongest empirical evidence supports the path model, supplemented by partial evidence for the sensitive period model, and further nuanced by processes of accumulation and social mobility.