Green tea is particularly rich in health-promoting flavonoids (which account for 30% of the dry weight of a leaf), including catechins and their derivatives. The most abundant catechin in green tea is epigallocatechin-3-gallate (EGCG), which is thought to play a pivotal role in the green tea's anticancer and antioxidant effects. Catechins can be considered right alongside of the better-known antioxidants like vitamins E and C as potent free radical scavengers and health-supportive for this reason.
Most of the research showing the health benefits of green tea is based on the amount of green tea typically consumed in Asian countries - about 3 cups per day (which would provide 240-320 mg of polyphenols). Just one cup of green tea supplies 20-35 mg of EGCG, which has the highest antioxidant activity out of all the green tea catechins.
The health benefits of green tea have been extensively researched and, as the scientific community's awareness of its potential benefits has increased, so have the number of new studies. Green tea drinkers appear to have lower risk for a wide range of diseases, from simple bacterial or viral infections to chronic degenerative conditions including cardiovascular disease, cancer, stroke, periodontal disease, and osteoporosis. So its age old use as a cure all has strong backing.