The bidirectional relationships among multimorbidity, depression, and catastrophic health expenditures in middle-aged and older Chinese adults: random-intercept, cross-lagged panel model

BACKGROUND: The evolving global disease landscape, in conjunction with the significant impact of an aging population, has led to mental‒physical multimorbidity, imposing unprecedented pressures on healthcare systems and economies. This study aimed to investigate the interrelationships among multimorbidity, depression, and catastrophic health expenditure (CHE) and to test whether the intensity of CHE mediates these links. METHODS: The analysis employed data from the China Health and Retirement Longitudinal Study (CHARLS), which conducted a longitudinal survey from 2011 to 2018, tracking 5,274 participants aged 45 years and older over a seven-year timeframe. Multimorbidity was ascertained through self-reported data from participants, whereas depression was evaluated via the 10-item Center for Epidemiologic Studies Depression Scale (CES-D-10). The intensity of CHE was calculated as the ratio of out-of-pocket (OOP) payments to the capacity to pay (CTP), adjusted for a catastrophic threshold of 40%. The relationships among the three variables were analysed via an extension of the random intercept cross-lagged panel model (RI-CLPM), which includes covariates to predict the observed variables. Mediation via the intensity of CHE was tested using 5,000 bootstrap resamples. RESULTS: At the between-person level, multimorbidity and depression were positively correlated (Model 1 r = 0.349; Model 2 r = 0.246; both p < 0.001), whereas the intensity of CHE showed negligible between-person associations with either variable. At the within-person level, all variables showed significant autoregressive stability, with multimorbidity demonstrating the strongest persistence (β = 0.808 in Model 1 and 0.936 in Model 2). Cross-lagged associations were clearly asymmetric, with prior multimorbidity exerting the largest prospective effects on the intensity of CHE (β = 3.028) and subsequent depression (β = 0.646 in Model 1 and β = 0.789 in Model 2), whereas prior depression and prior intensity of CHE had much smaller effects on later multimorbidity. Mediation analyses indicated that the intensity of CHE (T) partially mediated the association from multimorbidity (T‑1) to depression (T + 1) (indirect effect = 0.063, 95% CI [0.042, 0.084]), but showed negligible mediation for the reverse pathway from depression (T‑1) to multimorbidity (T + 1) (indirect effect = 0.001, 95% CI [0.000, 0.001]). CONCLUSIONS: The study identified asymmetric bidirectional relationships among multimorbidity, depression, and the intensity of CHE in Chinese middle-aged and older adults, with effects predominantly running from multimorbidity to increased intensity of CHE and later depression; the intensity of CHE explained only a small portion of the multimorbidity→depression effect and virtually none of the depression→multimorbidity pathway. Policies that integrate multimorbidity management with routine depression screening could help reduce the combined physical, psychological, and financial burdens among middle-aged and older adults.