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Prostate cancer is very common in Western countries but quite rare in Asian countries. Many researchers believe this is due to the large amounts of green tea consumed in Asian countries and several research studies have confirmed a link between green tea consumption and lower rates of prostate cancer.

The largest of these studies was carried out at the Research Center for Cancer Prevention and Screening at the National Cancer Center (NCC) in Tokyo, Japan. Data was gathered by questioning 49,920 men between the ages of 40 and 69 on their green tea drinking habits. During the 11 year study period, 404 of the men were diagnosed with prostate cancer (0.8%). 271 of the individuals had localized prostate cancer while 114 had advanced prostate cancer. 19 of the cases were of an indeterminate stage.

The study found that while green tea was only slightly correlated with a reduction in prostate cancer cases, there was a significant reduction in the number of advanced cases of prostate cancer in tea drinkers. In those who consumed 3-4 cups of tea a day, relative risk of prostate cancer was reduced by 17% while in those who consumed 5 or more cups of green tea daily, prostate cancer risk was reduced by as much as 48%.

The authors concluded that green tea consumption was associated with a decreased risk of developing advanced prostate cancer.

A Chinese study published in 2003 found an even greater correlation between green tea consumption and prostate cancer. The study was carried out by comparing 130 individuals in south-east China who had been diagnosed with prostate cancer to 274 control subjects who did not have prostate cancer.

This study found that those diagnosed with prostate cancer were less likely to be tea drinkers and that the longer an individual had been drinking green tea and the more green tea they consumed, the less likely they were to develop prostate cancer.

In total 55.4% of those diagnosed with prostate cancer were tea drinkers compared to 79.9% of the control group. Those who had been drinking green tea for over 40 years had an 88% reduced risk of developing prostate cancer, while those who consumed more than 1.5kg of green tea leaves yearly were 91% less likely to develop prostate cancer.

Finally, in an Italian study individuals who were at high risk of developing prostate cancer took either 600mg of green tea catechin (GTC) supplements daily for a year or a placebo. Just 1 of the 32 individuals who received the green tea catechin supplement developed prostate cancer during the one year study period compared to 9 out of 30 of the control group.

Catechins are polyphenolic antioxidants that make up approximately 25% of the dry weight of a fresh tea leaf.

Researchers believe one of the catechins in green tea called epigallocatechin gallate (EGCG) helps prevent cancer by encouraging apoptosis (a form of programmed cell death) of cancerous cells while leaving healthy cells unharmed. Furthermore high doses of green tea have been found to decrease testosterone levels and repress the androgen receptor gene - androgens have been shown to stimulate prostate cancer cell growth.