Socioeconomic inequalities in biological age: multidimensional gradients and cross-national heterogeneity in SHARE

Background: Associations between individual socioeconomic indicators and biological aging leave open whether the pattern extends across social origin, attained education, and economic resources. I examined these aspects of socioeconomic position and educational mobility in relation to Klemera-Doubal method (KDM) age acceleration across 12 countries in the Survey of Health, Ageing and Retirement in Europe (SHARE), and whether cross-country variation in these associations followed a welfare-state or economic-development pattern. Methods: Using SHARE Wave 6 (2015), I constructed three sex-specific KDM measures from overlapping biomarker panels in 10,043-14,015 adults aged 50-75 years and followed outcomes through Wave 9. Predictive validity was assessed for ADL/IADL limitations, cognition, and mortality. Survey-weighted models estimated pooled SES associations and tested country heterogeneity; exploratory analyses summarized multidimensional country profiles and examined six national indicators. Results: All three KDM measures were prospectively associated with incident functional limitation, lower cognition, and mortality; ADL/IADL odds ratios ranged from 1.29-1.61 and mortality hazard ratios from 1.44-1.92. Across all 21 pooled coefficients, greater socioeconomic advantage was associated with lower KDM age acceleration; each of the six specification-level tests had a false-discovery-rate-adjusted P<0.05 for every KDM outcome. KDM age acceleration was 0.076-0.107 SD lower per 1-SD higher respondent education and 0.060-0.076 SD lower per 10-percentile higher wealth or income rank. In joint origin-destination models, higher respondent-destination rank was consistently associated with lower KDM acceleration, whereas conditional parental-origin coefficients were smaller and compatible with zero. 11 of 18 country-heterogeneity tests had adjusted P<0.05; KDM9 respondent-education slopes ranged from -0.213 to 0.054 SD, with negative point estimates in 11 of 12 countries. Ordered country profiles showed no obvious welfare-state or economic-development hierarchy, and none of six contemporaneous national indicators robustly accounted for the variation after multiplicity adjustment. Conclusions: Across indicators of social origin, attained education, and current and accumulated economic resources, greater socioeconomic advantage was consistently associated with lower KDM age acceleration. The magnitudes of these associations also varied materially across affluent national settings and did not reduce to a welfare-state or economic-development ordering. Thus, pooled estimates capture a common pattern of socioeconomic stratification while potentially obscuring meaningful national variation in its strength; the absence of a simple contextual ordering adds a biological-aging dimension to the broader welfare-state puzzle.