 Green tea has been called nature's defense against cancer. Population studies linking green tea consumption with lower cancer risk has let some to advocate for the incorporation of green tea into the diet. After all, what's the downside? However, population studies can't prove cause and effects. It's not possible to determine whether green tea actually prevents cancer in people until you put it to the test. Intraepithelial Neoplasia is preceded by a precancerous condition known as intraepithelial neoplasia. Within one year, about 30% of such lesions turn into cancer. Because no treatment is given to patients until cancer is officially diagnosed, what a perfect opportunity to give green tea a try. So 60 men with precancerous prostate intraepithelial neoplasia were randomized into either a green tea group or a placebo group. It's hard to make a convincing placebo tea, so they used green tea pills, roughly equivalent to about 6 cups of green tea a day, compared to sugar pills. Six months into the study, they took biopsies from everyone, and in the placebo group, 6 out of 30 developed cancer by the halfway point, and then 3 of them remaining 24 by the end of the year. So 9 out of 30 in the placebo group developed cancer, or 30%, which is normally what happens when you don't do anything, about 30% go on to develop cancer within the first year. But in the green tea group, none developed cancer within the first 6 months, and only 1 by the end of the year. So only 1 out of the 30, nearly 10 times less than the placebo group. The first demonstration that green tea compounds could be very effective for treating pre-malignant lesions before prostate cancer develops. And even a year later, after they stopped the green tea, nearly 90% of the original green tea group remained cancer-free, while more than half of the placebo group developed cancer. This suggests that the benefits of the green tea may be long-lasting, overall nearly 80% reduction in prostate cancer. That is pretty impressive. What if you already have prostate cancer? A proprietary green tea extract supplement was given to 26 men with confirmed prostate cancer for an average about a month before they had their prostates removed, and there was a significant reduction in a number of cancer biomarkers, such as PSA levels, suggesting a shrinkage of the tumor. But there was no control group, and the study was funded by the supplement company itself. When an independent group of researchers tried to replicate the results in a randomized, double-blind, placebo-controlled trial, they failed to find any statistically significant improvement. So maybe green tea is only effective in the pre-cancerous state, but not powerful enough to impact overt prostate cancer. Green tea didn't seem to help with advanced metastatic cancer in the two studies that tried it, and recently doubt has been cast on the pre-cancerous results. When researchers tried to replicate it, the green tea extract group only seemed to cut prostate cancer development about in half, which, because of the small number of people in the study, may very well have happened just by chance. So where does that leave us? Unfortunately, green tea extract pills are not without risk. There's been about a dozen case reports of liver damage associated with their use, and so until there's more solid evidence of benefit, I'd stick with just drinking the tea. OK, green or black. Recent study randomized about 100 men with prostate cancer to consume 6 cups a day of green or black tea found a significant drop in PSA levels and NF-capabeta in the green tea group, but not the black tea or control groups. NF-capabeta is thought to be a prognostic marker for prostate cancer progression, and so the green tea appeared to work better than the black.