Longitudinal associations between impairment in Activities of Daily Living (ADL) and depressive symptoms in older adults: the mediating role of internet use based on longitudinal lagged mediation analysis in a decade-long five-wave prospective cohort

Abstract Background The mental health of older adults has emerged as a critical public health concern. Older adults who experience limitations in activities of daily living (ADLs) are at an increased risk of developing depression. Internet use may offer a promising strategy for reducing mental health risks among older adults. Objective To examine the longitudinal association between ADL impairment and depressive symptoms among Chinese older adults, and to investigate whether Internet use mediates this relationship. Methods We analyzed data from the China Health and Retirement Longitudinal Study (CHARLS), including 4194 participants aged ≥ 60 years in five waves( 2011, 2013, 2015, 2018, and 2020). The Activities of Daily Living (ADLs) scales were employed to assess ADL disability, while the10-item Center for Epidemiologic Studies Depression Scale (CESD-10, range 0–30) was utilized to measure depressive symptoms. Internet use was defined as self-reported use in the past month. Weighted probit and ordinary least squares (OLS) regression models were used to estimate the associations, with bootstrap tests (500 replications) for mediation. Results Internet use among participants increased from 0.79% in 2011 to 10.59% in 2020, while ADL disability increased from 17.38% to 27.59% over the same period. In weighted regression models, ADL disability was significantly associated with higher CESD-10 scores (β = 2.35, 95% CI: 2.13 to 2.57, p < 0.001). However, the bootstrap test of the indirect effect via Internet use was not statistically significant in the weighted population-level estimates (a × b = 0.27, BCa 95% CI: -0.45 to 3.55). Year-stratified analyses showed no significant indirect effects in any single year (all BCa 95% CIs contained zero). Conclusion ADL disability is a robust predictor of depressive symptoms among Chinese older adults. The mediating role of Internet use was not statistically significant in the weighted estimates, suggesting a modest pathway that warrants further investigation. Our findings highlight the importance of functional health maintenance for mental health promotion in aging populations, while recognizing the need for cautious interpretation of digital health interventions.