Mediating role of depressive symptoms in the association between trajectories of instrumental activities of daily living and all-cause mortality in middle-aged or older adults: a cohort study in South Korea.

The ability to independently perform instrumental activities of daily living (IADL) is important for the quality of life and social activities among older adults. This study examined the association between IADL trajectories and all-cause mortality and the mediating role of depressive symptoms. A total of 6033 participants aged ≥ 45 years were included. Longitudinal trajectories of IADL limitation, assessed using the Korean Instrumental Activities of Daily Living from 2006 to 2014, were clustered through group-based trajectory modeling. Depressive symptoms were determined by the 10-item Center for Epidemiologic Studies-Depression Scale. The associations between IADL limitation trajectories and all-cause death until 2024 were determined using Cox regression analyses. A mediation analysis was performed to assess the mediating role of depressive symptoms in this association. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated. Two distinct trajectories of IADL limitation were identified: stable low (n = 5757; 95.4%) and increasing (n = 276; 4.6%). The trajectory of increasing IADL limitations was associated with elevated risk for all-cause mortality (adjusted HR = 2.13; 95% CI = 1.79-2.52) compared to the trajectory of stable-low IADL limitations. Mediation analysis indicated that depressive symptoms partially explained the association between the increasing IADL limitation trajectory and all-cause mortality (adjusted indirect HR = 1.09; 95% CI = 1.05-1.15), with a proportion mediated of 16.0% (95% CI = 9.7-23.8). This longitudinal mediation analysis revealed that individuals experiencing an increasing trajectory of IADL limitations exhibited a higher risk of all-cause mortality, with depressive symptoms partially accounting for this association.