Association between neutrophil to lymphocyte ratio and depression among US adults: From a large population-based cross-sectional study

Objective: The study aims to determine the association between neutrophil to lymphocyte ratio (NLR) and depression and severity. Methods: We conducted a cross-sectional analysis of the National Health and Nutrition Examination Survey (NHANES). The Patient Health Questionnaire (PHQ-9) was administered to assess depression and its severity. NLR was calculated as a neutrophil count-to-lymphocyte count ratio. Results: The study included 22,207 adults (mean age, 44.43 years; women, 51.05%), and 1671 (6.54%) reported depression. The association between NLR and depression was not significant (odds ratio [OR], 1.06, 95% confidence interval [CI], 0.98 to 1.15, p = 0.12) after fully adjusting the covariates, and similar results (Q1 reference Vs Q2: OR, 0.87, 95%CI, 0.70 to 1.07 Vs Q3: OR, 0.99, 95%CI, 0.80 to 1.21 Vs Q4: OR, 1.08, 95%CI, 0.86 to 1.35, p for trend 0.21) when NLR as a categorical variable. After controlling for all confounding variables, a U-shaped relationship between NLR and depression severity was observed, and the inflection point was 1.78. Subgroup analyses showed a significant association among Mexican American/other Hispanic (OR, 1.13, 95%CI, 1.00 to 1.28, p = 0.04), non-Hispanic blacks (OR, 1.18, 95%CI, 1.07 to 1.32, p = 0.002), the subjects with poverty income ratio above four (OR, 1.24, 95%CI, 1.00 to 1.53, p = 0.048) between NLR and depression. The results from the sensitivity analyses remained stable. Conclusion: The association between NLR and depression is not general across depressed populations among US adults. This association may be specific to subgroups. The relationship between NLR and depression severity is non-linear.