Inflammation as a unique marker of suicide ideation distinct from depression syndrome among U.S. adults

•Inflammation's association with suicide ideation, distinct from depression, is unknown.•Few studies have evaluated the role of external inflammatory factors in suicide ideation.•Allergies, diet and biomarkers did not predict suicidal ideation in adults with depression.•Diet was associated with suicide ideation among those without depression. Recent evidence suggests that pro-inflammatory states may be independently associated with the risk of suicidality, above and beyond depression. This study assesses whether four indicators of inflammation, circulating levels of C-reactive protein (CRP), white blood cell (WBC) count and immunoglobulin E (IgE), and dietary inflammatory potential, measured using the Dietary Inflammatory Index® (DII), distinguish suicidal ideation (SI) from major depression (MD). Data come from multiple cycles of the US National Health and Nutrition Examination Survey (NCRP&WBC = 13,912; NDII = 17,076; NIgE = 4,060). MD was measured using the Patient Health Questionnaire-9 (PHQ-9); SI was indicated by the last item of the PHQ-9. To assess SI independent from MD, participants were classified into four categories: SI with MD, SI without MD, MD without SI, and neither MD nor SI. Regression models were used to assess the relationship between indicators of inflammation and SI with and without MD. None of the inflammatory indicators were able to distinguish SI status among MD cases. DII was associated with SI among individuals without MD. CRP, DII, and WBC were associated with MD. No associations were found for IgE. Cross-section data prevent drawing causal conclusions. Underreporting of MD and suicidal ideation and measurement of habitual diet using 24 h dietary recalls are also weaknesses. Dietary inflammatory potential was associated with suicide ideation among US adults with and without depression. Diet may play a role in suicide ideation and more empirical evidence is needed to determine whether nutritional protocols could aid in the treatment of suicidal behaviors. Findings did not support inflammatory factors having a relationship with suicide ideation distinct from depression.