The researchers harmonized data from the China Health and Retirement Longitudinal Study, the English Longitudinal Study of Ageing, the US Health and Retirement Study, the Korean Longitudinal Study of Ageing, the Mexican Health and Aging Study, and the Survey of Health, Ageing and Retirement in Europe. Socioeconomic position was represented by a four-level index combining baseline educational attainment and household wealth. Cohort-specific Cox proportional hazards models examined the incidence of limitations in activities of daily living, or ADLs, and instrumental activities of daily living, or IADLs. Continuous-time multistate Markov models estimated transitions among no, mild, moderate and severe dependency and, where mortality data were sufficiently reliable, death.

Compared with people in the highest socioeconomic group, those in the lowest group had a higher estimated hazard of incident ADL limitation in all six cohorts. For incident IADL limitation, positive associations were observed in most cohorts, while the low-versus-high estimate for the Mexican cohort was not statistically significant, with a hazard ratio of 1.31 and a 95% confidence interval of 0.84–2.06. Inequality measures across the full socioeconomic distribution pointed in the same direction. Distribution-standardised relative-index-of-inequality estimates ranged from 1.44 to 2.49 for ADL limitation and from 1.34 to 2.78 for IADL limitation across the cohort–outcome combinations.

The multistate models estimated how participants moved between different levels of functional dependency. Low socioeconomic position was associated with higher estimated transition intensities from no dependency to mild dependency and from mild to moderate dependency across all six cohorts, although the magnitude and precision of these estimates varied. Five-year model estimates showed a lower probability of remaining without dependency for the low socioeconomic group than for the high group: 0.641 versus 0.873 in CHARLS, 0.658 versus 0.841 in HRS, and 0.750 versus 0.890 in ELSA. These figures are cohort-specific model estimates rather than observed rates for every participant, and their differences show that the pattern was not uniform across settings.

Alternative specifications for socioeconomic position produced similar graded patterns in most cohorts. In a sensitivity analysis restricted to strict progression between dependency states, 46 of 54 deterioration-transition comparisons remained in the same direction as in the primary models. Some mortality estimates were imprecise, and confidence intervals were unavailable for the Korean cohort, limiting how confidently those findings could be interpreted. Taken together, the results link lower socioeconomic position with more frequent functional limitations and less favourable subsequent dependency patterns, but the magnitude and pattern of deterioration, recovery and mortality associations varied across cohorts and dependency states. The study therefore identifies a recurring association rather than a single universal trajectory of functional decline.

Subject of Research: Socioeconomic inequalities in functional dependency across six international ageing cohorts

Article Title: Socioeconomic position and functional dependency trajectories across six longitudinal ageing cohorts

Article References: Zhao, X., Gao, J., & Zou, W. (2026). Socioeconomic position and functional dependency trajectories across six longitudinal ageing cohorts. BMC Public Health. https://doi.org/10.1186/s12889-026-29665-3

Image Credits: AI Generated

DOI: 10.1186/s12889-026-29665-3

Keywords: socioeconomic inequality, functional dependency, healthy ageing, activities of daily living, instrumental activities of daily living, educational attainment, household wealth, longitudinal cohorts, Markov models, later-life health, Socioeconomic, position