Catechin compounds are found in the leaves of both green and black teas, but green teas have much higher levels of catechin than do black teas. Black and green teas differ only in how they are processed. Black tea leaves go through a fermentation process that gives the tea its characteristic dark color and tart flavor.

Catechins defeat cancer in at least one of three ways. First, they can prevent the formation of carcinogens, second, they turn up the body’s natural detoxification defenses, and finally, they suppress cancer promotion.

In the laboratory, animal studies have shown that catechins have other promising qualities: acting as an antibacterial and antiviral agent, regulating cholesterol and blood pressure, and reducing blood clotting tendencies that may cause heart attacks or strokes.

Epidemiological studies (how diseases are distributed in populations) aren't yet conclusive, but suggest that those populations that drink more green tea live longer than those that don't.