Drinking green tea associated with reduced risk of advanced prostate cancer
A report published online on September 29, 2007 in the American Journal of Epidemiology described the finding of an association in Japanese men between drinking green tea and a reduced risk developing advanced prostate cancer.
Researchers at Japan’s National Cancer Center in Tokyo utilized data from the Japan Public Health Center-based Prospective Study, which involved two cohorts enrolled in 1990 and 1993. The current analysis included a total of 49,920 men aged 40 to 69 upon enrollment who were followed until the end of 2004. Questionnaires completed by the cohorts after enrollment were analyzed for amount and frequency of green tea consumption, and participants were categorized according to their intake.
By the end of the follow up period there were 404 cases of prostate cancer diagnosed, of which 114 were advanced (having spread beyond the prostate), 271 localized (confined to the prostate), and 19 were of an undetermined stage. Although drinking green tea was not found to have an effect on localized prostate cancer, it was dose-dependently associated with a decrease in advanced prostate cancer risk. Men in the top category of green tea intake, who consumed five or more cups per day, had nearly half the risk of developing advanced prostate cancer compared with those who consumed less than one cup per day.
The study is the first, to the authors’ knowledge, to examine the association between green tea and prostate cancer according to stage, and to determine the protective benefit of green tea on advanced prostate cancer. They posit the induction of apoptosis, cell growth inhibition, and cell cycle progression arrest as mechanisms for green tea’s effects, and add that EGCG, a compound believed to be responsible for many of tea’s benefits, has been found to prevent tumor cell invasion as well as the expression of matrix metalloprotease, an enzyme which is overexpressed in angiogenesis.
Although the researchers’ results are supported by a number of animal studies, they recommend well-designed human trials to confirm their findings.
Long-term consumption of tea catechins is common in China and Japan. The frequency of the latent, localized type of prostate cancer (PC) does not vary significantly between Eastern and Western cultures, but the clinical incidence of metastatic PC is generally lower in Japan and other Asian countries, in contrast to the common occurrence of metastatic PC in Europe and the United States. One possible explanation is that EGCG consumption in green tea in Asian countries prevents the progression and metastasis of PC cells. This explains the lower mortality rate due to PC and breast cancer in Asian countries as compared to Western countries.
In regards to PC, there are now studies that show that vitamin E and selenium use will decrease the incidence as well as the mortality from PC. The ATBC study by Heinonen et al. (J. Natl. Cancer Inst., 1998) demonstrated a 32% decrease in the incidence of PC and a 41% lower mortality rate from PC in men taking alpha-tocopherol (vitamin E). Another study by Fleshner et al. (J. Urol., 1998) showed a reduction in growth rates of transplanted LNCaP cells in athymic mice induced by a high-fat diet (40.5%) by dl-alpha tocopherol (synthetic vitamin E). The landmark study by Clark et al. (JAMA, 1996) provided evidence that 200 mcg of selenium could reduce the incidence of PC by 63%. This is consistent with the observation that selenium inhibited the growth of DU-145-an androgen-independent human cell line of PC-by 50% at a selenium dose of 1 × 10-6 M and by 98% at a dose of 10-4 M.
Research reported in the October 1, 2007 issue of the Journal of Nutrition suggests that increasing the intake of soy protein may help lower the risk of developing prostate cancer by favorably altering estrogen metabolism. Reduced urinary excretion of estradiol (an estrogen), and a lower ratio of 2-hydroxy estrogens to 16 alpha-hydroxyestrone are likelier to occur in prostate cancer patients than in men without the disease.
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