Dynamic interplay between depressive symptoms, healthy lifestyle, and frailty in middle-aged and older adults: a cross-cohort longitudinal study

Frailty is influenced by psychological and behavioral factors. While depressive symptoms and unhealthy lifestyles are independent risk factors, their joint effects and population heterogeneity remain under-characterized. Using CHARLS (2011–2020) and ELSA (2010–2021) data, we employed time-varying Cox models, latent class growth analysis, and random intercept cross-lagged panel models (RI-CLPM) to examine the independent and joint associations of depressive symptoms and lifestyle with frailty. The baseline Cox analytic samples included 3,171 CHARLS and 6,402 ELSA non-frail participants. Depressive symptoms elevated frailty risk (CHARLS: HR = 1.117; ELSA: HR = 1.313), while healthy lifestyle scores reduced risk (HR = 0.865 and 0.735, respectively). Frailty hazards varied markedly across joint depression-lifestyle trajectory groups. RI-CLPM revealed substantial between-person variance (ICC = 0.30–0.70) and minimal cross-lagged effects, indicating that the observed associations were more consistent with stable between-person differences than with consistent within-person temporal associations over the observed follow-up period. Age and education were significant effect modifiers. Depressive symptoms and healthy lifestyle were independently and jointly associated with frailty. RI-CLPM findings indicated that these associations were more consistent with stable between-person differences, with no consistent bidirectional within-person temporal associations detected over the observed follow-up period.