We examined plasma concentrations of phyto-oestrogens in relation to risk for subsequent prostate cancer in a case–control study
nested in the European Prospective Investigation into Cancer and Nutrition. Concentrations of isoflavones genistein, daidzein and
equol, and that of lignans enterolactone and enterodiol, were measured in plasma samples for 950 prostate cancer cases and 1042
matched control participants. Relative risks (RRs) for prostate cancer in relation to plasma concentrations of these phyto-oestrogens
were estimated by conditional logistic regression. Higher plasma concentrations of genistein were associated with lower risk of
prostate cancer: RR among men in the highest vs the lowest fifth, 0.71 (95% confidence interval (CI) 0.53–0.96, P trend ¼ 0.03). After
adjustment for potential confounders this RR was 0.74 (95% CI 0.54–1.00, P trend ¼ 0.05). No statistically significant associations
were observed for circulating concentrations of daidzein, equol, enterolactone or enterodiol in relation to overall risk for prostate
cancer. There was no evidence of heterogeneity in these results by age at blood collection or country of recruitment, nor by cancer
stage or grade. These results suggest that higher concentrations of circulating genistein may reduce the risk of prostate cancer but do
not support an association with plasma lignans