Cancer prevention by tea polyphenols

The cancer preventive activities of tea (Camellia Sinensis Theaceae) have been investigated extensively in laboratory and human studies. Green tea polyphenols, mainly catechins, have shown inhibitory activities against tumorigenesis in different animal models, including those for cancers of the lung, oral cavity, esophagus, stomach, small intestine, colon, bladder, liver, pancreas, skin, prostate and mammary glands. Similar activities have also been reported in some human studies. This chapter reviews the nature of these inhibitory actions and discusses possible mechanisms involved. These inhibitory activities are attributed to catechins, especially the most abundant (—)-epigallocatechin-3-gallate (EGCG). The antioxidant or pro-oxidant activities of catechins and their binding to molecular targets would affect signal transduction and metabolic pathways that enhance apoptosis, suppress cell proliferation, and inhibit angiogenesis, resulting in the inhibition of carcinogenesis and cancer cell growth. Tea is considered a healthy beverage. However, the effect of tea consumption on the prevention of cancer in humans still needs to be further investigated. This chapter discusses some future directions in this area of research and concerns about possible toxicity, especially with high doses of tea polyphenols in tablet form.