"Both green and black teas might prevent cancer, heart disease and arthritis."

In recent test-tube studies, a compound called EGCG, a powerful antioxidant in tea, inhibited an enzyme that cancer cells need in order to grow. The cancer cells that couldn't grow big enough to divide self-destructed.  It would take about 4 cups of green tea a day to get the blood levels of EGCG that inhibited cancer in the study. Black tea also contains EGCG, but at much lower concentrations.

USA Today, Feb 2, 2000