Abstract
<title>Abstract</title> <p>Purpose Multimorbidity is associated with depression, but the contribution of patient-paid medical costs remains uncertain. We examined prospective associations between somatic chronic disease burden, out-of-pocket (OOP) medical spending, and depressive symptoms in middle-aged and older adults in China. Methods We analyzed 24,861 adjacent-wave transitions contributed by 14,043 adults aged 45 years or older in the China Health and Retirement Longitudinal Study, 2011–2018. The exposure was a count of 12 somatic chronic conditions; the outcome was next-wave 10-item Center for Epidemiologic Studies Depression Scale (CESD-10) score. Annualized OOP spending combined outpatient and inpatient payments. Marginal models used participant-clustered robust standard errors. An observational product-of-coefficients decomposition used 500 participant-cluster bootstrap repetitions. Results Each additional condition predicted 0.496 more next-wave CESD-10 points (95% confidence interval [CI] 0.446–0.546). Compared with no condition, one, two, and three or more conditions predicted 0.658, 1.287, and 1.901 additional points, respectively. Each condition was associated with higher odds of any OOP spending (odds ratio 1.342, 95% CI 1.313–1.371) and 11.6% higher spending among positive spenders. OOP spending was associated with subsequent CESD-10 score (beta = 0.046, 95% CI 0.026–0.067). The indirect association was 0.0229 points (bootstrap 95% CI 0.0136–0.0332), corresponding to 4.6% attenuation (95% CI 2.7%-6.8%). Conclusion Multimorbidity showed a graded longitudinal association with depressive symptoms. OOP spending was a detectable but quantitatively modest pathway, supporting integrated mental health care alongside stronger financial protection.</p>