Background: The association of neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR), and monocyte to lymphocyte ratio (MLR) with depression has been investigated extensively while the results were conflicting. We aim to investigate whether NLR, PLR, and MLR are associated with depression, as well as to explore the potential non-linear relationship between them.
Methods: This cross-sectional study was conducted based on representative samples of US adults from the National Health and Nutrition Examination Survey 2005-06 to 2017-18. Major depression was defined as a 9-item Patient Health Questionnaire of 10 or more. Multivariable logistic regression models were used to calculate the odds ratio of depression in relation to NLR, PLR, and MLR with the first quartile of their values as the reference. Restricted cubic splines (RCS) were added to the regression model to estimate the non-linear relationship between NLR, PLR, or MLR and depression.
Results: A total of 34,324 participants were included in the study and 3009 of them were diagnosed with major depression. Only PLR was significantly associated with depression after adjustment of all covariates in the multivariable logistic regression analysis. RCS showed that NLR was significantly associated with depression after adjustment of all covariates and NLR, PLR, and MLR were associated with depression in a non-linear manner.
Limitations: The cross-sectional design did not imply any causal inferences.
Conclusion: NLR and PLR were associated with depression after adjustment of potential confounders in a non-linear manner. Prospective studies might be needed to further reveal the non-linear relationships.
Keywords: Major depression; Monocyte to lymphocyte ratio; Neutrophil to lymphocyte ratio; Platelet to lymphocyte ratio; Restricted cubic splines.
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