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Background: Our previous case-control study revealed that the Japanese residents in Japan could be divided into those who are able to degrade daidzein, a soybean isoflavone, to equol and those without this ability, and that the incidence of prostate cancer is higher in the latter group., Methods: We recently conducted a similar case-control study involving not only Japanese residents in Japan but also Korean residents in Korea. The incidence of prostate cancer in Korean residents is known to be close to that of Japanese residents in Japan. On the other hand, American residents in the United States have a markedly higher incidence of prostate cancer as compared to Japanese residents in Japan., Results: The number of subjects was 295 in Japan (133 patients and 162 controls), 122 in Korea (61 patients and 61 controls) and 45 in the United States (24 patients and 21 controls). The percentage of equol producers among patients and controls was 29% and 46% in Japan (P = 0.004) and 30% and 59% in Korea (P = 0.001), respectively. The active isoflavone level was markedly lower and the percentage of equol producers was also lower (17% for patients and 14% for controls) for Americans as compared to the Japanese and Koreans., Conclusions: These results suggest that the ability of producing equol or equol itself is closely related to the lower incidence of prostate cancer. The results also suggest that a diet based on soybean isoflavones will be useful in preventing prostate cancer.

Objectives: To establish a Japanese version of the National Institutes of Health Chronic Prostatitis Symptom Index (NIH-CPSI) and to determine its validity and applicability in patients with chronic prostatitis, comparing the results with those from patients with benign prostatic hyperplasia (BPH) and normal men., Methods: The study included 103 patients with chronic prostatitis, 60 with BPH, and 87 normal men who agreed to respond to a self-administered questionnaire of the Japanese version of the NIH-CPSI (JPN-NIH-CPSI). Testing-retesting was done to confirm the reliability of the index in 23 patients with chronic prostatitis, with a 2-week interval between tests., Results: Pain or discomfort was more prominent in the prostatitis group than in the BPH and normal groups. Overall, quality of life in the prostatitis group was impaired more severely than that in the other two groups. The scores of three domains (pain, urinary symptoms, and quality-of-life impact) in the prostatitis group were clearly higher than those in the BPH and normal groups, except for those of urinary symptoms in the BPH group. The test-retest analysis showed good reliability and internal consistency for the JPN-NIH-CPSI, with a Cronbach's alpha coefficient of more than 0.8., Conclusions: The JPN-NIH-CPSI can be reliably used for evaluation of Japanese patients with prostatitis, as is the NIH-CPSI for English-speaking men.