Because of its special aroma,
green tea is a popular beverage consumed by some human populations worldwide. In recent years, many laboratory studies have shown that in a variety of animal
tumor bioassay systems the administration of
green tea, specifically the polyphenolic fraction isolated from
green tea leaves (
green tea polyphenols), affords protection against
cancer induction. In mouse skin
tumor bioassay systems, topical application of
green tea polyphenols to skin has been shown to result in protection against a)
3-methylcholanthrene-induced skin tumorigenicity, b) 7,12-dimethylbenz(a)
anthracene (DMBA)-induced skin
tumor initiation, c) 12-O-tetradecanoylphorbol-13-
acetate and other
tumor promoters caused
tumor promotion in DMBA-initiated skin, and d)
benzoyl peroxide- and
4-nitroquinoline N-oxide caused enhanced malignant progression of nonmalignant lesions.
Green tea extract has also been shown to cause partial regression of established skin
papillomas in mouse. Similarly, chronic oral feeding of
green tea polyphenols or water extract of
green tea has also been shown to result in the protection against both chemical
carcinogen- and ultraviolet B radiation-induced skin tumorigenicity. Collectively these data suggest that
green tea possesses significant chemopreventive effect against each stage of
carcinogenesis, and that it may be useful against inflammatory responses associated with the exposure of skin to chemical
tumor promoters as well as to solar radiation. Available data regarding the mechanism by which
green tea affords these diversified effects is discussed.