Role of age in the association of chronic conditions and multimorbidity with incident ADL disability: multicohort analyses of 108,810 adults

Chronic conditions and multimorbidity are increasingly prevalent in ageing populations, and their impact on disability remains poorly understood. This study investigated the association of chronic conditions and multimorbidity at ages 50, 60, 70, and 80 years with the subsequent onset of disability. Data from 108,810 participants (54% women, mean age 61.2 ± 9.8 at baseline) from the Health and Retirement Study, the English Longitudinal Study of Ageing, and the Survey of Health, Ageing, and Retirement in Europe were used. The number of chronic conditions was determined from a list of eight conditions. Cox regression was used to examine the incidence of disability in activities of daily living (ADL). ADL disability per 1000 person-years was 14.2 (13.7, 14.7) at age 50, 22.4 (21.9, 22.9) at age 60, 34.3 (33.4, 35.1) at age 70, and 67.6 (65.6, 69.6) at age 80. Having one chronic condition at age 50 was associated with a hazard ratio (HR) for ADL disability of 1.50 (1.42, 1.58) and 1.22 (1.13, 1.42) at age 80. For individuals with three or more chronic conditions, the HRs were 3.05 (2.79, 3.33) at age 50 and 1.74 (1.61, 1.87) at age 80. Analysis of population attributable fraction suggests that between 5.0 and 29.4% of incident disability, depending on the intervention scenarios and age at onset of chronic diseases, could be reduced by acting on chronic diseases. Chronic conditions and multimorbidity demonstrated a strong association with the onset of ADL disability, highlighting the need for early intervention to mitigate future disability risks.