Mediating role of the Dietary Index for Gut Microbiota in the association between depression and cardiovascular health among US adults

Background Depression is closely associated with cardiovascular health, and gut microbiota–related dietary patterns may represent a potential biological pathway linking the two. This study aimed to examine the association between depressive symptoms and cardiovascular health as defined by Life’s Essential 8 (LE8), and to evaluate the mediating role of the Dietary Index for Gut Microbiota (DI-GM) in this association. Methods The study included 18,071 adults aged ≥ 20 years from the US National Health and Nutrition Examination Survey (NHANES) 2007–2018. The primary outcome was LE8 cardiovascular health rating (low/moderate/high), with LE8 continuous total score as supportive outcome; depression was assessed by Patient Health Questionnaire (PHQ-9). Survey-weighted ordinal logistic regression and linear regression were used to assess the association between depression and DI-GM and LE8. Restricted cubic spline (RCS) was used to evaluate the dose-response relationship, and counterfactual (g-computation) mediation analysis was used to explore the mediating effect of DI-GM. Effect modification was also examined in subgroups. Models were adjusted for age, sex, race/ethnicity, marital status, education level, and poverty-to-income ratio (PIR). Results After adjusting for potential confounders, each 1-point increase in PHQ-9 was associated with a 9% reduction in the cumulative odds of having a higher LE8 score (OR = 0.91, 95% CI: 0.90–0.93), whereas each 1-point increase in DI-GM was associated with a 46% increase in the cumulative odds of having a higher LE8 score (OR = 1.46, 95% CI: 1.42–1.51) (both P < 0.001). DI-GM partially mediated the association between depression and LE8, the total natural indirect effect was statistically significant (TNIE OR = 0.996, 95% CI 0.993–0.999, P = 0.008), accounting for 5.08% (95% CI 1.35–8.87%) of the total association, estimated within a counterfactual mediation framework. This mediating pathway was more pronounced among women (mediation proportion: 6.0%) and individuals with comorbid gastrointestinal diseases (14.2%). Dose–response analyses indicated that these associations generally followed a monotonic pattern. Conclusions A greater burden of depressive symptoms was associated with poorer cardiovascular health as assessed by LE8, suggesting that gut microbiota-related dietary patterns may partially mediate the association between depression and cardiovascular health. DI-GM may represent a potential modifiable target, particularly among women and individuals with comorbid gastrointestinal diseases. However, the temporal sequence and underlying mechanisms of these associations require further validation through longitudinal and intervention studies.