The dietary inflammatory index is inversely associated with depression, which is minimally mediated by C-reactive protein.

Depression affects 8% of adults in America and is one of the leading causes of disability in Western countries. The dietary inflammatory index (DII) has previously been reported to be associated with inflammation and depression. However, no study to date has looked at the potential mediating effect of inflammation on the association of DII and depression. We hypothesized that the association of DII and depression would be both statistically and clinically mediated substantially by inflammation. We assessed these associations using the cross-sectional National Health and Nutrition Examination Survey (NHANES) 2005-2010 database. Our analysis included 10,022 participants aged 20 years and older. Inflammation was assessed with C-reactive protein (CRP) levels. Diet was measured using two 24 hour dietary recalls. Depression was assessed using the 9-item Patient Health Questionnaire (PHQ-9), which has a score range of 0 to 27, with the higher score showing more severe depressive symptoms. Comparing the highest to lowest DII quartiles, the mean score difference for depression was 0.47 units (95% CI 0.24-0.70, P-trend <.001) in the multivariable adjusted model. In the sex-stratified models, the results remained significant only among females, with the mean score difference of 0.72 (95% CI 0.34-1.10, P-trend <.001). CRP mediated 3.6% of the association between DII and depression in the total population in the fully adjusted model, which was statistically significant (P-trend <.001) but not clinically significant. No mediation association was found in the sex-stratified models. Further studies are needed to assess the associations with various inflammatory biomarkers in larger and more diverse populations.