Dietary inflammatory index mediates the relationship of social determinants of health with blood pressure and obesity in the United States: a cross-sectional study of NHANES 2009–2018

Purpose Social determinants of health (SDoH) and dietary Inflammatory Index (DII) are pivotal factors in population health. However, whether DII mediates the impact of SDoH on blood pressure and obesity remains insufficiently characterized. This study aimed to quantify the associations among SDoH burden, blood pressure, obesity, and DII, and to further explore the mediating role of DII.Methods Data from 22,870 participants in NHANES 2009–2018 were analyzed. Weighted multivariable linear regression (LR) and restricted cubic spline (RCS) models were used to estimate β coefficients and characterize dose-response relations. Subgroup analyses and stratified RCS were conducted to assess heterogeneity. Mediation analyses were then performed to systematically evaluate the mediating effect of DII on these associations.Results After all covariates were adjusted, each one-unit increase in the SDoH score was associated with significant increases in SBP (β = 0.59, 95% CI: 0.39–0.80), DBP (β = 0.18, 95% CI: 0.03–0.33), PP (β = 0.42, 95% CI: 0.21–0.62), ABSI (β = 0.20, 95% CI: 0.15–0.26), BMI (β = 0.12, 95% CI: 0.01–0.22), and DII (β = 0.15, 95% CI: 0.13–0.17). RCS analyses demonstrated nonlinear relationships with these indices. Mediation analyses indicated that DII mediated the effects of adverse SDoH on SBP, PP, hypertension, ABSI, and BMI, with mediation proportions of 5.92%, 9.89%, 11.52%, 10.93%, and 20.00%, respectively.Conclusions Adverse SDoH were positively associated with blood pressure and obesity, with DII acting as an important mediator. These findings underscore the importance of jointly considering SDoH and dietary inflammation in the development of prevention and intervention strategies for hypertension and obesity.