Higher dietary phytochemical index is associated with lower odds of infertility: a case-control study

Dietary phytochemicals possess antioxidant and anti-inflammatory properties, yet their relationship with female infertility remains unclear. We examined the association between the Dietary Phytochemical Index (DPI) and infertility, and whether oxidative stress/inflammatory biomarkers mediate this link.

This case-control study included 400 women (200 infertile, 200 fertile). Cases were clinically diagnosed infertility patients; controls had ≥1 live birth. DPI was calculated from food-frequency questionnaires. Fasting biomarkers (MDA, HOMA-IR, hs-CRP, IL-6, TNF-α, TAC) were measured. Logistic regression evaluated DPI-infertility associations, and bootstrap mediation analysis tested indirect effects through biomarkers.

Infertile women had significantly lower DPI (28.2 ± 8.4 vs. 34.1 ± 9.8, p < 0.001). Each 1 unit increase in DPI was associated with 7% lower odds of infertility (OR 0.931, 95% CI: 0.909-0.953). Expressed per 10 unit increment (a more clinically interpretable change), this corresponds to approximately 48% lower odds (OR 0.48, 95% CI: 0.39-0.59). Women in the highest DPI tertile had 80% lower odds than those in the lowest (OR 0.205, 95% CI 0.119-0.352), with a significant dose-response trend (p < 0.001). DPI was inversely associated with MDA, HOMA-IR, hs-CRP, and IL-6 (all p < 0.05), but none of the examined biomarkers significantly mediated the DPI-infertility association (all indirect effect 95% CIs included zero; maximum proportion mediated: 12.6% for HOMA-IR). The direct effect of DPI remained significant in all models.

Higher dietary phytochemical intake shows a strong independent association with lower infertility odds in this exploratory case-control study. Causal inference is precluded by design limitations. In exploratory mediation analyses, circulating oxidative stress and inflammatory biomarkers did not significantly mediate this association; however, this finding does not exclude local tissue level or alternative mechanistic pathways. Prospective studies are needed to establish causality and elucidate mechanisms.