Phyto-oestrogens and prostatic growth

The incidence of and mortality from prostatic cancer in the West is higher than that in Asian countries. Migrants from Asia to western countries, who maintain their traditional diet, do not have an increased risk of prostatic cancer. This has been attributed in part to 'phyto-oestrogens' in vegetarian Asian diets. Prostatic cancer is a hormone-dependent disease and oestrogens retard the growth of prostatic tumours by interfering with the action of testosterone. Oestrogen increases the level of sex hormone-binding globulin that binds testosterone, resulting in lower free testosterone levels, thereby decreasing androgenic stimulation of the prostate. Oestrogens used to retard the growth of prostatic cancer are associated with certain undesirable side-effects. Phyto-oestrogens have weak oestrogenic potency and anticancer effects. Thus, these phytochemicals have a possible role in the prevention of hormone-dependent diseases such as prostatic cancer. Although the relative potencies of various phyto-oestrogens compared with oestradiol are low, the oestrogen receptor (ER) complexes formed byoestradiol and isoflavones have functional similarities. Also, phyto-oestrogens have a higher affinity to bind to ER-beta than ER-alpha. They are antiproliferative and inhibit tyrosine and other protein kinases which play a key role in tumorigenesis, and also inhibit the production of the potent androgen 5alpha dihydrotestosterone in the prostate. Since prostatic cancer cells usually multiply slowly and the development of this cancer can take many years before symptoms appear, the latent period provides a chemopreventive opportunity for natural therapy with phyto-oestrogens. Although phyto-oestrogens have not yet been used in long-term trials to evaluate their ability to reduce the risk of prostate carcinoma, the evidence thus far suggests that they have a protective effect against the growth of prostate tumours.