Intake of dietary flavonoids and risk of epithelial ovarian cancer

Background: The impact of different dietary flavonoid subclasses on risk of epithelial ovarian cancer is unclear, with limited previous studies that have focused on only a few compounds. Objective: We prospectively examined associations between habitual flavonoid subclass intake and risk of ovarian cancer. Design: We followed 171,940 Nurses' Health Study and Nurses' Health Study II participants to examine associations between intakes of total flavonoids and their subclasses (flavanones, flavonols, anthocyanins, flavan-3-ols, flavones, and polymeric flavonoids) and risk of ovarian cancer by using Cox proportional hazards models. Intake was calculated from validated food-frequency questionnaires collected every 4 y. Results: During 16-22 y of follow-up, 723 cases of ovarian cancer were confirmed through medical records. In pooled multivariateadjusted analyses, total flavonoids were not statistically significantly associated with ovarian cancer risk (HR for the top compared with the bottom quintile: 0.85; 95% Cl: 0.66, 1.09; P-trend = 0.17). However, participants in the highest quintiles of flavonol and flavanone intakes had modestly lower risk of ovarian cancer than did participants in the lowest quintile, although the P-trend was not significant [HRs: 0.76 (95% Cl: 0.59, 0.98; P-trend = 0.11) and 0.79 (95% CI: 0.63,1.00; P-trend = 0.26), respectively]. The association for flavanone intake was stronger for serous invasive and poorly differentiated tumors (comparable HR: 0.68; 95% CI: 0.50, 0.92; P-heterogeneity = 0.10, P-trend = 0.07) compared with nonserous and less-aggressive tumors. Intakes of other subclasses were not significantly associated with risk. In food-based analyses used to compare subjects who consumed > 1 and <= 1 cup black tea/d, the HR was 0.68 (95% CI: 0.51, 0.90; P < 0.01). Conclusions: Higher intakes of flavonols and flavanones as well as black tea consumption may be associated with lower risk of ovarian cancer. Additional prospective studies are required to confirm these findings.