Associations of dietary and blood inflammatory indices with anemia in U.S. adults: Evidence from NHANES 2007 to 2018

This study aimed to examine the potential interactions between Dietary Inflammatory Index (DII), Systemic Immune-Inflammation Index (SII), Systemic Inflammatory Response Index (SIRI), and their joint associations with the prevalence of anemia in the American population. This retrospective cross-sectional survey utilized data from the National Health and Nutrition Examination Survey 2007 to 2018. The study included a total of 19,368 adults aged equal to or >18 years residing in the United States. The DII was computed based on 27 dietary components to reflect the inflammatory characteristics of the diet. The SII was calculated as the platelet count × neutrophil count/lymphocyte count. The SIRI was calculated as the neutrophil count × monocyte count/lymphocyte count. To explore the associations of DII, SII, and SIRI with anemia, we conducted logistic regression analysis, restricted cubic spline analysis, and subgroup analysis. The research included a sample of 19,368 individuals, of whom 1770 (9.14%) were identified as having anemia. After adjusting for covariates, we observed a significantly higher risk of anemia in the highest tertile group of the DII, SII, and SIRI compared to the lowest tertile group of inflammation markers, with increased odds of anemia of 53%, 68%, and 41%, respectively. The dose-response relationship was linear for DII but exhibited nonlinear threshold effects for SII and SIRI. Furthermore, when analyzing the combinations of DII with SII and DII with SIRI, we found that groups with high levels of inflammatory markers consistently had a higher risk of anemia. This association was most pronounced in women. Moreover, higher SII and SIRI were inversely associated with hemoglobin levels in anemic individuals, indicating a link with disease severity. In conclusion, this study shows that higher dietary and systemic inflammation are independently and jointly associated with an increased anemia prevalence in US adults. The association appeared strongest when high dietary and systemic inflammation coincided, with the risk being most pronounced in women. These findings highlight anti-inflammatory diets as a potential strategy for anemia prevention.