A number of health claims have been made for green tea(http://www.jcm.co.uk/bookshop/v3/tea/news.phtml), claiming that its polyphenol content has antioxidant properties that can help prevent cancer. There is also the suggestion that it can increase endurance in exercise by improving fat metabolism.
An article in New Scientist magazine (20 March 2004) mentions that numerous studies suggest that green tea protects against a range of cancers, including lung, prostate and breast cancer. The secret is the antioxidant epigallocatechin gallate (EGCG), according to Hirofumi Tachibana's team at Kyushu University in Japan. Their research showed that growth of human lung cancer cells that have a cell receptor called 67 LR is slowed significantly after drinking just two or three cups of green tea, which contains EGCG. The research also showed that 67 LR is involved in the propagation of prion diseases such as mad cow disease in humans. So knowledge of EGCG's effect on 67 LR might have implications in the treatment of these diseases too. (Full report in Nature Structural and Molecular Biology, DOI:10.1038/nsmb743).
According to the U.S. National Cancer Institute, in laboratory studies using animals, catechins scavenged oxidants before cell damage occurred, reduced the number and size of tumors, and inhibited the growth of cancer cells. White tea is said to be even more effective. However, human studies have proven more contradictory, perhaps due to such factors as variances in diet, environments, and populations.
Clinical trials conducted by the University of Geneva, in Switzerland indicate that green tea raises metabolic rates and speed up fat oxidation. In addition to caffeine, green tea contains catechin polyphenols that raise thermogenesis (the rate at which calories are burned) and hence increases energy expenditure
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