Relationship of serum levels and dietary intake of isoflavone, and the novel bacterium Slackia sp strain NATTS with the risk of prostate cancer: a case-control study among Japanese men

Isoflavones may play a role in the prevention of hormone-related cancers. Equol is an isoflavone metabolized from daidzein in the presence of certain intestinal bacteria. Slackia sp. strain NATTS, a newly identified equol-producing bacterium, was recently isolated from human feces in Japan. We investigated the association of serum levels and dietary intake of isoflavones and Slackia sp. strain NATTS with the risk of prostate cancer in a case-control study among Japanese men. Fifty-six patients with newly diagnosed prostate cancer and 56 hospital controls were enrolled in this study. Isoflavones were assessed by measurement of serum levels and administration of a food frequency questionnaire. Slackia sp. strain NATTS in feces was also measured. The odds ratios (ORs) and 95 % confidence intervals (CIs) for prostate cancer were then determined using a logistic regression model. The adjusted ORs for prostate cancer in comparison with the highest to lowest categories were 0.06 (95 % CI 0.02-0.24) for serum genistein, 0.18 (95 % CI 0.06-0.52) for daidzein, 0.16 (95 % CI 0.06-0.46) for glycitein, 0.52 (95 % CI 0.22-1.22) for equol, 0.86 (95 % CI 0.30-2.48) for dietary genistein, and 0.80 (95 % CI 0.28-2.28) for dietary daidzein. The adjusted OR for prostate cancer in comparison with values above versus below the median was 0.95 (95 % CI 0.42-2.16) for Slackia sp. strain NATTS. Our study findings suggest that high serum levels of genistein, daidzein, and glycitein are significantly associated with a decreased risk of prostate cancer among Japanese men.