Dietary isoflavones may protect against prostate cancer in Japanese men

Author: Nagata Y, Sonoda T, Mori M, Miyanaga N, Okumura K, Goto K, Naito S, Fujimoto K, Hirao Y, Takahashi A, Tsukamoto T, Akaza H
Publication: J Nutr. 2007 Aug;137(8):1974-9

Japanese men have a significant lower prostate cancer incidence rates than men from other countries. At least as long as they live in Japan, because Japanese men living in Hawaii have 6 times higher prostate cancer rates than their counterparts in Japan. This indicates that not only genetics but also environmental factors, such as diet, play an important role. The Japanese diet is relatively high in soy product, especially tofu and natto, containing high levels of isoflavones.

Nagata and co-workers at the Sapporo Medical University School of Medicine in Japan investigated the association between isoflavones intake and the prevalence of prostate cancer. They conducted a case-control study involving 200 prostate cancer patients and 200 controls and found that isoflavones, genistein and daidzein were significantly linked with decreased prostate cancer risk. The odds ratio for the fourth category (quarter with highest isoflavones intake) vs the first category (quarter with lowest isoflavones intake) was 0.42, 0.58 and 0.55 for total isoflavones, genistein and daidzein respectively. Polyunsaturated fat intake was also significantly associated with decreased prostate cancer risk. Previous experimental studies have already demonstrated that isoflavones induced apoptosis of prostate cancer cells and results in growth inhibition and cell cycle arrest. One intervention study also demonstrated that men who consumed higher quantities of phytoestrogens had a reduced risk of prostate cancer development and progression.

The authors concluded that isoflavones might be an effective dietary protective factor against prostate cancer in Japanese men