Green tea could prevent cancer due to its special ingredient, epigallocatechin gallate, which is found mainly in (670 g/kg) in green tea extract. Green tea is also known to contain cateclins with antioxidant properties.

To explore this claim, scientists treated cells grown with or without green tea extract with iron as an oxidative stimulus for two hours. Supplementation with green tea extract significantly decreased malondialdehyde production and DNA damage after iron oxidative treatment. Malondialdehyde is a lipid peroxidative product, which is believed to be a marker of radical generation and tissue damage. There was no effect on membrane distribution of n-3 fatty acids due to iron treatment in cells that were not treated with green tea, according to the Journal of Nutrition 99 (Vol 129, Iss 12, pp 2130-2134).

Information provided is courtesy of and compiled by the Academy of Anti-Aging Research staff, editors, and other reports.
 

While numerous studies continue to show green tea's anti carcinogenic effect, we continue to advise against tea drinking because there are simply better ways to get the antioxidant from sources other than green tea. For example, Vitamin C and E are strong antioxidants that don’t have the stimulatory side effects. Moreover, green tea contains caffeine, which is a stimulant and is not recommended for those with cardiovascular disease.