Independent and joint associations of depressive symptoms and social isolation on trajectories of functional disability among middle-aged and older adults

With accelerating population aging in China, functional disability has become a major health problem among middle-aged and older adults. Previous research has shown that depressive symptoms and social isolation are associated with the occurrence and development of functional disability. However, less is known about the independent and joint associations of depressive symptoms, social isolation, and functional disability trajectories among middle-aged and older Chinese adults. A total of 5639 participants aged 45 + were obtained from the China Health and Retirement Longitudinal Study (CHARLS). In 2011 (baseline), depressive symptoms were measured using the 10-item Center for Epidemiologic Studies Depression Scale (CESD-10); social isolation was assessed via four dimensions (marital status, residence, social engagement, frequency of contact with children). Functional disability was measured using the activities of daily living and instrumental activities of daily living. Participants with 2011 (baseline) data and at least 1 reassessment of functional disability during follow-ups (2013, 2015, 2018, and 2020) were included. Group-Based Trajectory Modeling (GBTM) identified trajectories of functional disability over 9 years of follow-up (2011–2020). Multinomial logistic regression models explored the independent and joint associations of depressive symptoms and social isolation with these trajectories. Four trajectories of functional disability were identified: low (56.04%), moderate (33.82%), high (6.30%), and worsening (3.85%). Independent effects of depressive symptoms and social isolation were significant across all trajectories, with the strongest impacts observed in the high trajectory group: depressive symptoms (Relative Risk [RR] = 3.99, 95% confidence intervals [CI] = 2.92–5.47) and social isolation (RR = 2.11, 95%CI = 1.54–2.89). Participants with both depressive symptoms and social isolation had higher risks for the moderate (RR = 2.85, 95%CI = 2.25–3.62) and the high trajectory groups (RR = 7.52, 95%CI = 4.79–11.81) compared to those without depressive symptoms and social isolation. This study found that participants with depressive symptoms and social isolation were at a higher risk of experiencing trajectories of moderate and high functional disability, providing new insights into prevention strategies.