Associations of activities of daily living disability and instrumental activities of daily living disability with all-cause mortality: Evidence from Five Major Longitudinal Studies

Background
With the global aging of the population, it is increasingly crucial for older people to maintain their independence through activities of daily living (ADL) and instrumental activities of daily living (IADL). There is evidence that ADL/IADL disability is associated with increased mortality, but there is still limited evidence of this in middle-aged and old people globally.

Methods
We conducted a multi-cohort pooled study using data from five major longitudinal studies in the Global Aging Dataset: the Health and Retirement Study (HRS), China Health and Retirement Longitudinal Study (CHARLS), Survey of Health, Aging and Retirement in Europe (SHARE), English Longitudinal Study of Aging (ELSA), and Mexican Health and Aging Study (MHAS). We used Cox proportional hazard models to examine the associations of ADL and IADL disabilities with mortality. Furthermore, we conducted analysis to explore the interaction between ADL and IADL on mortality, and further mediation analysis to explore the roles of chronic diseases, depression, and socioeconomic status in the association.

Findings:
The final sample included 10,089 participants from CHARLS, 7,218 from ELSA, 20,702 from HRS, 12,411 from MHAS, and 33,650 from SHARE. The Cox proportional hazards model revealed that ADL/IADL disabilities were significantly associated with increased mortality across all cohorts. The pooled results showed that the hazard ratio (HR) for mortality with one disability in terms of ADL was 1.31 (95% CI: 1.13, 1.52) compared with those without disabilities, while it was 1.84 (1.41, 2.42) for two or more disabilities. Meanwhile, the HR was 1.44 (1.28, 1.62) for one disability in terms of IADL, but 2.11 (1.66, 2.69) for two or more disabilities. Significant mediating effects of chronic diseases and depression were found across all cohorts. The most pronounced additive interaction was observed in CHARLS, with relative excess risk due to interaction (RERI) of 2.29 (95% CI: 0.70, 3.89).

Interpretation:
This study provides evidence that ADL/IADL disabilities significantly elevate the long-term mortality risk among middle-aged and old people. Chronic diseases and depression substantially mediate this association. Our findings underscore the disproportionate health inequities faced by individuals with disabilities and highlight the urgent need for global health systems to adapt, ensuring that people with disabilities are better understood and included in health policies and services.