Association between immune-inflammation-based prognostic index and depression: An exploratory cross-sectional...

Immune-inflammatory mediators influence numerous immune and inflammatory pathways, elevating the likelihood of depression. The systemic immune-inflammation index (SII) emerges as an innovative prognostic indicator, integrating various peripheral blood immune cell subpopulations, specifically neutrophils, platelets, and lymphocytes. This exploratory study aims to examine the correlation between SII and depression.

Data from the 2005-2020 National Health and Nutrition Examination Survey (NHANES) were utilized. Depression was diagnosed with a Patient Health Questionnaire score of 10 or higher. The relationship between log2-SII and depression incidence was analyzed using a restricted cubic spline (RCS). Logistic regression was employed to calculate the odds ratio of depression concerning log2-SII. In cases of non-linearity, piecewise linear models with change points were applied to assess the associations in both the overall population and specific subgroups. Additionally, subgroup analyses were conducted to determine the applicability of the findings to particular populations.

A total of 42,133 participants were included in the study, comprising 49.32 % men and 50.68 % women, with an average age of 47.02 ± 17.45 years. RCS analysis demonstrated a J-shaped non-linear relationship between log2-SII and depression incidence. When log2-SII was ≥8.50, SII showed a positive association with depression incidence, even after adjusting for covariates. Additionally, each unit increase in log2-SII corresponded to an 18 % rise in depression incidence (OR = 1.18, 95 % CI: 1.10-1.27). Subgroup analysis further revealed that the association between SII and depression incidence varied across different populations.

Due to the cross-sectional nature of NHANES, causality or long-term implications cannot be inferred. Further research is needed to ascertain if a longitudinal relationship exists between SII and depression.

Our findings suggest a significant and complex non-linear association between SII and depression. However, further basic and prospective studies are necessary to explore SII's impact on depression and clarify its underlying mechanisms. Additionally, these studies will provide a foundation for personalized interventions targeting the immune-inflammatory processes in patients with depression and elevated SII.