Background: Isoflavones, which are included in soybeans, have been suggested to protect against prostatecancer. Equol, one of isoflavones, is an intestinally derived bacterial metabolite of daidzein. A newly identifiedequol-producing bacterium, Slackia sp. strain NATTS, with a high equol-producing activity was isolated fromhuman feces in Japanese adults. Counts of Slackia sp. strain NATTS in intestinal flora have not been assessedwith regard to prostate cancer risk. In this study, we investigated the association of serum isoflavones andcounts of Slackia sp. strain NATTS with prostate cancer risk in a case-control study. Materials and
Methods:Concentrations of isoflavones and counts of Slackia sp. strain NATTS in feces were measured from 44 patientswith prostate cancer and 28 hospital controls. The risk of prostate cancer was evaluated in terms of odds ratios(ORs) and 95% confidence intervals (CIs) by the logistic regression analysis.
Results: The detection proportions ofSlackia sp. strain NATTS in cases and controls were 34.1% and 25.0%, respectively. Counts of Slackia sp. strainNATTS were significantly correlated with serum concentrations of equol both in cases and controls (Spearmancorrelation coefficients, rs=0.639 and rs=0.572, p<0.01, respectively). Serum concentrations of genistein, daidzein,glycitein, and equol were not significantly associated with risk of prostate cancer.
Conclusions: This study foundthat counts of Slackia sp. strain NATTS correlated with serum concentrations of equol both in prostate cancercases and controls, but serum isoflavone concentrations were not associated with risk of prostate cancer in ourpatients.