Associations between the Dietary Inflammatory Index and Depression among Pregnant and Postpartum Women: Analysis of NHANES 2005–2018

Jian Qiao¹Aiqing Han²Yannv Qu³Li Zhang^2*

• ¹Jinan Mental Health Center, jinan, China
• ²Jinan Maternity and Child Care Hospital, Jinan, China
• ³Peking University Shenzhen Hospital, Shenzhen, China

Background: Chronic low-grade inflammation has been implicated in the pathophysiology of perinatal depression. The Dietary Inflammatory Index (DII) is a validated measure of the inflammatory potential of a diet. This study examined the association between DII and depression among pregnant and postpartum women, with a focus on potential nonlinear effects. Methods: Data from 1,093 pregnant or postpartum (within 18 months) women in the NHANES 2005–2018 survey were analyzed. Dietary intake was assessed via 24-hour recall to calculate DII scores. Depressive symptoms were measured using the PHQ-9. Weighted multivariate logistic regression was used to estimate ORs for depression in relation to DII scores, and weighted linear regression was used to assess the association between DII scores and PHQ-9 total scores. We tested for nonlinear relationships using a generalized additive model. A log-likelihood ratio test was used to compare a two-piecewise model to a single-linear-term model. Sensitivity analyses were conducted to check the robustness of the findings. Results: The mean age of pregnant and postpartum women was 28.88 (95% CI 28.34–29.42) years. 7.1% participants met the criteria for moderate/severe depression (PHQ-9 score ≥10). About 21.9% of the sample had a highly proinflammatory diet (DII >2.87). A non-linear association between DII and depression (P = 0.008 for the threshold effect). In adjusted weighted logistic models, among women with DII > 2.87, each 1-unit increase in DII was associated with an OR = 2.81 for depression (95% confidence interval 1.07–7.38, P = 0.039). Consistently, in the weighted linear regression, when the DII exceeded 2.87, each additional DII point corresponded to an increase of β = 1.59 points in the PHQ-9 score (95% CI 0.02–3.17, P = 0.047). The associations remained significant and of similar magnitude in the sensitivity analyses. Conclusions: In this cross-sectional study, a higher Dietary Inflammatory Index was associated with a greater risk of depression, but this relationship was markedly nonlinear. Diets with a very high proinflammatory potential were linked to significantly increased odds of perinatal depression, whereas more anti-inflammatory diets did not result in a further decrease in depression risk below that threshold.