Exploring the mediating role of Charlson comorbidity index in the association between body mass index and depression in U.S. adults: NHANES 2007-2020.

Objective: The relationship among body mass index (BMI), Charlson comorbidity index (CCI), and depression forms a complex interplay that affects both physical and mental health. However, whether CCI mediates the association between BMI and depression remains unclear. In this study, we aimed to elucidate the mediating role of CCI in the relationship between BMI and depression.

Methods: This study used data from the National Health and Nutrition Examination Survey, a program of the National Center for Health Statistics in the United States, including 23,639 participants from 2007 to 2020. Wilcoxon rank-sum and Rao-Scott adjusted chi-square tests were employed to compare characteristics between adults with and without depression. Weighted logistic regression and restricted cubic spline models were applied to investigate the pairwise associations among BMI, CCI, and depression. Mediation analysis was performed to assess whether CCI mediated the relationship between BMI and depression.

Results: Of the 23,639 participants, 2128 (9.0 %) had depression. Significant associations were observed between BMI and CCI; CCI and depression; and BMI and depression (P < 0.001). A U-shaped relationship between BMI and depression odds was identified, with the lowest odds at a BMI of 23 kg/m. Mediation analysis revealed that CCI partially mediated the BMI-depression relationship, accounting for 19.5 % of the total effect.

Conclusions: The results suggest that CCI plays a mediating role in the association between BMI and depression, and that improved chronic disease management may be associated with lower odds of depression in high BMI populations.