Contribution of caffeine to the anticarcinogenic activity of green tea

Caffeine (1,3,7-trimethylxanthine) is a major component of tea that may contribute to its anticarcinogenic activity. It is present in green and black tea, comprising 5% of all solids and in 1.25% (w/v) brew is present at a concentration of about 220 ^g ml-1 (Wang et al., 1994). The ability of caffeine to modulate the tumorigenicity of chemicals is well documented. However, caffeine has been demonstrated to both inhibit and potentiate chemically induced cancers in rats and mice (Nomura, 1976; Hiroshino and Tanooka, 1979; Denda et al., 1983; Welsch et al., 1988a). Similarly, some epidemiological studies established correlations between coffee consumption and certain cancers (MacMahon et al., 1981; Boyle et al., 1984) whereas others failed to detect an association (Rosenberg et al., 1985; Wynder et al., 1986). A comparison of the anticarcinogenic potential of green and black teas with that of their decaffeinated derivatives against ultraviolet B (UVB) light-induced skin carcinogenesis in mice showed that the decaffeinated teas were markedly less effective and at a high dose even exacerbated the carcinogenic response (Huang et al., 1997). Adding caffeine back to the decaffeinated teas restored their higher anticarcinogenic activity thus establishing, at least in this case, a role for caffeine. The decaffeinated teas, however, displayed a similar anticarcinogenic activity against UVB-induced skin cancer in mice initiated with 7,12-dimethylbenz[a]anthracene (Wang et al., 1994). The fact that decaffeinated teas also displayed anticarcinogenic activity in this animal model indicates that other components in green and black tea also possess anticarcinogenic properties. Whether the presence of caffeine in the tea affords protection against chemically induced cancers remains to be established.

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