The J-shaped association between the ZJU index and depression: A cross-sectional study from NHANES

Previous studies have confirmed that the ZJU index is effective in capturing trends in metabolic disorders and disease risk. However, no study has statistically analyzed the relationship between the ZJU Index and depression. This study included data from 16,008 participants sourced from the National Health and Nutrition Examination Survey 2005-2018. Weighted multivariable logistic regression and generalized additive models were used to explore the independent and nonlinear relationships between the ZJU index and depression. A 2-piece linear regression model was used to estimate threshold effects, along with subgroup analyses and interaction tests. To account for multiple testing in subgroup analyses, P values for interaction were additionally adjusted using the Benjamini-Hochberg false discovery rate procedure. A total of 16,008 participants were included, with 7.42% classified as having depression. The prevalence of depression initially decreased and then increased across the ZJU index quartiles (Q1: 6.35%; Q2: 5.38%; Q3: 6.83%; Q4: 11.32%; P < .0001). Both unadjusted and adjusted models demonstrated that higher ZJU index levels were associated with increased depression risk. In Model III, each unit increase in the ZJU index was associated with a 1.4% higher likelihood of depression (Model III: odds ratio (OR) = 1.014, 95% confidence interval (CI): 1.006, 1.022). Curve fitting indicated a J-shaped association between the ZJU index and depression, with a breakpoint (K) of 35.386. To the left of this breakpoint, the ZJU index showed a negative association with depression (OR = 0.948, 95% CI: 0.917-0.980), while to the right, a positive association was observed (OR = 1.022, 95% CI: 1.013-1.032). Subgroup analyses and interaction tests revealed that the association between the ZJU index and depression was dependent on drinking status and diabetes presence (P < .05). Among individuals who consumed alcohol or had diabetes, a positive association between the ZJU index and depression was observed, whereas no significant association was found among nondrinkers or those without diabetes, where the ZJU index and depression showed a nonlinear relationship. There is a J-shaped association between the ZJU index and depression, suggesting that a higher ZJU index may be linked to an increased risk of depression.