Functional dependency level and later-life incident multimorbidity in older people: longitudinal evidence from 19 countries in China and Europe

Background: Population aging and increasing life expectancy raised concerns about functional dependency (FD) and multimorbidity. However, the impact of FD on later-life multimorbidity remains poorly understood. Method: Participants from the China Health and Retirement Longitudinal Study (CHARLS) and the Survey of Health, Ageing and Retirement in Europe (SHARE) with complete baseline FD and 7-year follow-up data on multimorbidity were included, excluding those with multimorbidity or missing specific chronic diseases at baseline. FD levels, measured by inability to perform basic activities of daily living (ADLs) and instrumental activities of daily living (IADLs) at baseline wave, were categorized into five cumulative-score groups. Multimorbidity was defined as the presence of two or more chronic diseases. Logistic regression was employed to analyze the association of FD with incident multimorbidity and individual chronic diseases in each cohort. Cohort-specific estimates were combined using random-effects meta-analysis. Stratified analyses and interaction tests assessed modifications of associations. Results: Compared to individuals without dependency, the risk of developing incident multimorbidity at 7-year follow-up with 2 FDs were significantly increased (2.13 [1.33–3.42] for ADL, 1.30 [1.02–1.66] for IADL), nearly doubling among patients with ≥ 4 FDs (1.52 [1.37–1.69] for ADL, 1.78 [1.18–2.69] for IADL). Significant associations between FDs and incident multimorbidity were observed across various subgroups, demonstrating dose-response relationships. Both cohorts exhibited positive interaction effects of age, gender, residential area, marital status, and social isolation on the associations between ADL dependency and incident multimorbidity. Conclusions: FD emerged as a significant risk factor for later-life multimorbidity, displaying interactions with demographic and social factors. This underscores the urgency for tailored interventions, integrated care models, and a reorientation of healthcare services to mitigate potential adverse health outcomes.