To make green tea, the leaves are picked and preserved (usually by steaming or baking) to keep them from undergoing the process of fermentation (or oxidation).
Oolong tea is exposed to the sun and allowed to partially ferment; black tea is fermented completely.
Approximately 90 percent of the polyphenols found in green tea are called catechins (KAT-uh-kins).
EGCG is the most active component in green tea, and is a stronger antioxidant than either vitamin C or E. For this reason, it is the most widely studied green tea compound.
Epidemiological studies (mostly conducted in Asian populations) have consistently associated green tea consumption with lower incidence of many different cancers.
A 1989 study in the Japanese Journal of Nutrition reported that in tea-producing regions of Japan (where residents consume green tea in several forms, including gum, candy and desserts) stomach cancer mortality rates are lower than in other regions of Japan.
One of the first studies to suggest a protective effect of green tea appeared in the journal Cancer Research in 1994.
In a case-control study conducted at the Shanghai Cancer Institute in China that appeared in the Journal of the National Cancer Institute in 1994, green tea drinkers had a 50 percent reduction in risk for esophageal cancer.
A study published in 1998 involving Stage I and Stage II breast cancer patients in Japan showed that subjects who drank more than five cups of green tea a day had a lower recurrence rate and longer disease-free period than subjects who drank four or less cups per day.
A database search of the published scientific literature showed that over 100 separate scientific papers on EGCG's potential anti-cancer benefits have been published in peer-reviewed journals in 2005 alone.