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• All tea comes from the plant Camellia sinensis.  The tender, new leaves are picked for making tea.  Green tea is prepared by lightly steaming the leaves immediately after picking.  This process destroys the enzymes which would normally break down the active compounds in the leaf and thus preserves the polyphenols.  Black tea, which is more popular in the United States, is made by allowing the picked leaves to oxidize, which adds flavor to the tea but also breaks down some of the active ingredients in tea.  After oxidation, black tea contains polyphenol pigments called theaflavins.

What are the active ingredients in green tea?

• Green tea is an antioxidant and contains certain types of polyphenols called catechins.  The average cup of tea (120 mL) contains 60 mg of polyphenols.  Antioxidants are substances that scavenge and seize oxidants, which are unstable molecules produced by the human body.  In order for these molecules to become stable, they damage cell proteins and genetic material in order to obtain the electrons necessary for stability.  The damaged cells are thought to be more prone to certain diseases, such as cancer.  Antioxidants, such as green tea, inhibit this process.
• The main catechins found in green tea are epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC).  Of these, EGCG is thought to be the primary polyphenol in green tea extract.

Why study green tea?

• Catechins have shown inhibitory activity against tumorigenesis in laboratory studies and in mouse studies.  Studies in humans have been done and continue to be done to evaluate the effectiveness of green tea extract in human disease.  The underlying mechanism for green tea's anticancer effect remains to be determined.