Association of Immune-inflammation-based prognostic index with depression: A cross-sectional analysis of NHANES data

Abstract

Abstract Background: Immune-inflammatory mediators might modulate a wide range of immune and inflammatory processes，resulting in an increased risk of depression. The objective of this study was to assess the association between Systemic Immune-inflammation Index (SII) and depression through a population-based retrospective cohort of the National Health and Nutrition Examination Survey from 2005 to 2020. Methods: The 2005–2020 data of enrolled participants from the National Health and Nutrition Examination Survey were selected. Among them, non-pregnant adults with complete data of SII and Patient Health Questionnaire-9 (PHQ9) questionnaire were included in the study. The depression was assessed with PHQ9 questionnaire. The restricted cubic spline (RCS) was used to flexibly simulate the association of SII with the incidence of depression. Taking SII as an independent variable and the incidence of depression as a dependent variable, logistic regression analysis was conducted to analyze the correlation between SII and the incidence of depression. We further transformed SII from a continuous variable to a classified variable (tierce) for sensitivity analysis. A series of subgroup analysis were used to explore whether the research results applied to specific people. Where there was evidence of non-linearity, piecewise-linear models with change points were fitted for depression of overall participants and specific populations to quantify associations. Results: After screening, a total of 42,133 subjects were finally included in the study. After adjusting for covariates, the RCS analysis indicated that log2-SII was associated with the incidence of depression in a J-shaped curve with a nonlinear relationship, and the inflection point of the curve was log2-SII=8.50 (95%CI: 8.42-8.57). We estimated that log2-SII was in the range of 8.42-8.57, and the incidence of depression was the lowest, with a positive correlation above (P < 0.05) and a negative correlation below (P > 0.05). When log2-SII > 8.50, the incidence of depression increased by 18% (OR=1.18, 95%CI: 1.10-1.27) with one additional unit of log2-SII. The results of subgroup analysis suggested that the correlation between SII and the incidence of depression was not consistent in different subgroups. Conclusion: In conclusion, our findings suggest that SII was significantly associated with depression regardless of the potential confounders in a complicated non-linear manner. Further basic andprospective studies are needed to explore the effect of SII on depression.