Isoflavones in Japanese and Caucasian men with prostate cancer in Hawaii.

Abstract

241 Background: Recently, several studies have reported that soy isoflavones and the ability to produce Equol, an active derivative of soy isoflavone, may play a role in the suppression of prostate cancer. An Equol-producing bacterium, Slackia sp. strain NATTS has been identified in stool cultures. To further investigate this relationship, we evaluated Japanese-Americans (JA) and whites (W) in Hawaii, with and without prostate cancer, with regards to dietary soy intake, serum isoflavone levels, and the presence of stool NATTS. Methods: The serum levels of Daidzein, Genistein, Glysitein, Dihydrodaidzein (DHD), Equol, o-desmethylangolensin (o-DMA) and total isoflavone was determined in 65 JA (34 patients with prostate cancer , 31 controls) and 68 W (34 patients with prostate cancer , 34 controls) subjects. The control group consisted of age matched cancer-free male subjects. To evaluate Equol producing ability, we assessed the presence of NATTS in stool samples. All subjects completed a lifetime dietary soy consumption survey. Results: The serum level of Genistein and o-DMA were significantly higher in JA (Genistein: W 21.5±54.0, JA 61.8±150.9, p=0.04; o-DMA: W 0, JA 2.0±7.9, p=0.04). Daizein level trended higher in JA (W 13.9±34.7, JA 33.3±84.0, p=0.09). Glysitein level was significantly higher in W (W 35.7±10.4, JA 30.7±15.5, p=0.03). No differences were noted in DHD and Equol levels between W and JA. Total isoflavone level trended higher in JA (W 76.3±104.9, JA 135.1±245.6, p=0.07). There were no differences in serum isoflavone level between prostate cancer patients and controls for both JA and W. Only 10 of 120 stool samples were positive for NATTS (8.6%), a rate much lower than seen in Japan. JA showed higher intake of soy than W. Conclusions: The high soy consumption and isoflavone levels in JA may be related to the observed lower incidence of prostate cancer relative to W in Hawaii. The near absence of equal producers in Hawaii JA may contribute to their higher incidence of prostate cancer compared to Japan based Japanese. These results suggest that both soy isoflavone levels and Equol production may be inversely associated with prostate cancer incidence.