Background: Flavonoids are phytochemicals that are present in plant-based foods such as tea, wine, fruits, vegetables, and cocoa. Animal and cell culture studies indicate a chemopreventive effect of flavonoids on prostate cancer via mechanisms related to anti-inflammation, induction of apoptosis, antioxidation, cell cycle regulation, and impairment of angiogenesis. However, few epidemiological studies have examined associations between flavonoid intake and prostate cancer in humans.

Methods: Data from 920 African-American (AA) and 977 European-American (EA) newly-diagnosed prostate cancer patients from the North Carolina-Louisiana Prostate Cancer Project (PCaP) were used to assess the association between flavonoid intake and prostate cancer aggressiveness. Diet was assessed using a modified version of the National Cancer Institute (NCI) Diet History Questionnaire. The USDA recently released the 2011 USDA Database for the Flavonoid Content of Selected Foods, which allowed for estimation of intake of five subclasses of flavonoids that were summed to calculate total flavonoid intake. Men were classified as cases (high aggressiveness) if Gleason sum ≥8, or PSA >20 ng/ml, or Gleason sum ≥7 AND clinical stage = T3c-T4c. All other men constituted the comparison group (low and intermediate aggressiveness). Odds ratios (OR) and 95% confidence intervals (95%CI) were calculated for high aggressiveness prostate cancer by tertile of flavonoid intake using logistic regression with adjustment for potential confounders.

Results: The highest tertile (compared to the lowest tertile) of total flavonoid intake appeared to be inversely associated with prostate cancer aggressiveness after adjustment for age, race, education, smoking status, and screening history (OR=0.75, 95%CI= 0.54, 1.04). Estimated odds of high aggressiveness prostate cancer with increasing flavonoid intake were reduced further by smoking and age, such that inverse associations were strongest in men <65 years of age (OR=0.62, 95%CI=0.40, 0.98 and OR=0.67, 95%CI=0.42, 1.06 for the middle and highest tertiles, respectively) and in current smokers (OR=0.25, 95%CI=0.11, 0.54 and OR=0.48, 95%CI=0.22, 1.06 for the middle and highest tertiles, respectively). Results did not differ by race. Orange and grapefruit juices and tea were the main contributors to total flavonoid intake in both AA and EA men.

Conclusions: Total flavonoid intake was inversely associated with prostate cancer aggressiveness in this large case-only study. Stratified analyses revealed that current smokers and younger men may receive the most benefit from increased flavonoid intake. This study provides clinical evidence that suggests a plant-based diet may prevent aggressive prostate cancer.

Citation Format: Rebecca R. George, Susan E. Steck, L. Joseph Su, James L. Mohler, Elizabeth T.H. Fontham, Jeannette T. Bensen, James R. Hebert, Hongmei Zhang, Lenore Arab. Flavonoid intake and prostate cancer aggressiveness among African Americans and European Americans in PCaP. [abstract]. In: Proceedings of the Eleventh Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2012 Oct 16-19; Anaheim, CA. Philadelphia (PA): AACR; Cancer Prev Res 2012;5(11 Suppl):Abstract nr A103.