Prostate cancer.
Laboratory studies have found that green tea extracts prevent the growth of prostate cancer cells in test tubes. In a large clinical study in Southeast China researchers found that the risk of prostate cancer went down with increasing frequency, duration, and quantity of green tea consumption. However, both green and black tea extracts also stimulated genes that cause cells to be less sensitive to chemotherapy drugs. People who are undergoing chemotherapy should ask their doctors before drinking green or black tea, or taking tea supplements.