Tea in chemoprevention of cancer

This review summarizes available information on epidemiological and experimental data showing an association of tea consumption with cancer prevention. Studies showing cancer risk associated with tea consumption are also summarized. Tea is grown in about 30 countries and, next to water, is the most widely consumed beverage in the world. Experimental studies demonstrating the chemopreventive effects of tea have been conducted principally with green tea; limited studies have also assessed the usefulness of black tea. Majority of these studies have been carried out in skin tumor model system where consumption through drinking water of water extracts of tea or a polyphenolic fraction isolated from tea has been shown to afford protection against chemical carcinogen- or ultraviolet radiation-induced skin tumorigenesis. Tea consumption has also been shown to afford protection against chemical carcinogen-induced lung, forestomach, esophagus, duodenum, pancreas, liver, breast and colon carcinogenesis in specific bioassay models. Evidence has also accumulated showing that tea polyphenols prevent tumor promoter- and ultraviolet B-induced inflammatory responses in murine skin. The species and strains of animals, dose, route, frequency and duration of carcinogen administration, as well as types, route of administration and duration of tea or its polyphenolic component(s) treatment are described in detail. A brief description regarding mechanism(s) responsible for the broad chemopreventive effects of tea is provided. Epidemiologic studies, though inconclusive, in general suggest a possible preventive effect of tea consumption on human cancer. On the basis of available information, epidemiologic and experimental studies are ongoing to draw the possible relationship between tea consumption and cancer causation and prevention. Appropriate strategies for future clinical chemoprevention trials to translate animal data to human cancer risk are warranted.