Chain mediating effect of somatic pain and sleep duration between chronic disease count and depressive symptoms in older adults.

BACKGROUND: Population aging has intensified concerns regarding mental health in older adults. Multimorbidity is highly prevalent in late life and is strongly associated with both somatic pain and depressive symptoms. Somatic pain and abnormal sleep duration are common in older adults and may mediate the relationship between chronic disease burden and depression. However, the potential chain mediating roles of somatic pain and sleep duration between chronic disease count and depressive symptoms remain unclear. AIM: To examine whether somatic pain and sleep duration independently and sequentially mediate the association between chronic disease count and depressive symptoms in older adults. METHODS: A total of 213 older adult patients who visited the First People's Hospital of Zunyi from March 2020 to March 2024 were selected as the research subjects. Data were collected using a general information questionnaire, the Chronic Disease Checklist, the Short-Form McGill Pain Questionnaire (SF-MPQ), and the 10-item Short-Form Center for Epidemiological Studies Depression Scale (CES-D-10). SPSS 26.0 and PROCESS 4.1 macro program were used for correlation analysis, regression analysis, and bootstrap mediation effect test. RESULTS: The depression detection rate was 40.38%. Chronic disease count, sleep duration, somatic pain, and depressive symptoms were significantly correlated (all P < 0.01). After covariate adjustment, chronic disease count had a significant direct effect on depressive symptoms (β=0.164, 95% CI: 0.056-0.273). The independent mediating effects of somatic pain (effect=0.122, 95% CI: 0.057-0.187) and sleep duration (effect=0.054, 95% CI: 0.021-0.096), as well as the chain mediating effect of "somatic pain → sleep duration" (effect=0.018, 95% CI: 0.006-0.037), were all significant. The total indirect effect accounted for 54.17% of the total effect. CONCLUSION: Somatic pain and sleep duration independently and sequentially mediate the association between chronic disease count and depressive symptoms in older adults. Integrated strategies targeting multimorbidity control, pain management, and sleep regulation may help reduce depression risk. However, the chain-mediated effect was small in magnitude, suggesting that direct interventions targeting pain and sleep may offer more clinically meaningful benefits than long-chain approaches. Given the cross-sectional design, causal directions cannot be inferred.