Frailty–depressive symptom transitions in relation to subsequent change in function-weighted multimorbidity burden: a longitudinal CHARLS study, 2011–2018

Abstract Background Frailty and depressive symptoms often coexist in middle-aged and older adults and may precede increasing multimorbidity burden. However, it remains unclear whether different frailty–depressive symptom transition patterns are associated with subsequent changes in function-weighted multimorbidity burden and whether high-risk patterns are disproportionately concentrated among socioeconomically disadvantaged groups. Methods We used four waves (2011–2018) of the China Health and Retirement Longitudinal Study. Joint frailty and depressive-symptom states in 2011 and 2013 were grouped into seven two-wave transition patterns. Outcomes during 2013–2018 were annualized change in the Chinese multimorbidity-weighted index (CMWI) and upper-quartile CMWI growth. Associations were estimated using multivariable linear regression and modified Poisson regression with community-clustered robust standard errors. Repeated CMWI measurements were examined with linear mixed-effects models. Concentration indices assessed socioeconomic inequalities in persistent dual vulnerability and upper-quartile CMWI growth. Results Among 8,133 participants, 2,016 (24.8%) had upper-quartile CMWI growth. In primary Model A, persistent dual vulnerability showed the largest mean difference in annualized CMWI change compared with stable low risk (0.203 points/year, 95% CI 0.155–0.252) and the highest risk ratio for upper-quartile growth (RR 2.15, 95% CI 1.88–2.46). In secondary baseline-conditional Model B, the corresponding estimates were 0.271 points/year (95% CI 0.222–0.321) and RR 2.19 (95% CI 1.91–2.51). Model A marginal standardization gave an adjusted absolute risk difference of 20.5 percentage points (95% CI 16.4–24.6). Associations remained positive after excluding the mental-health-related component of the CMWI. Persistent dual vulnerability was concentrated among participants with lower household consumption (Erreygers index − 0.0586, 95% CI − 0.0799 to − 0.0387). Upper-quartile CMWI growth showed no clear socioeconomic concentration, and there was no clear evidence of multiplicative interaction on the risk-ratio scale (joint Wald P = 0.706). Conclusions Persistent co-occurrence of frailty and depressive symptoms was associated with the largest estimated subsequent increase in function-weighted multimorbidity burden. This pattern was disproportionately concentrated among participants with lower socioeconomic status. Joint assessment of frailty and depressive symptoms may help identify individuals at higher risk of increasing multimorbidity burden, although intervention studies are needed to determine whether targeted management can improve subsequent outcomes.