INHIBITORY EFFECTS AND TOXICITY OF GREEN TEA POLYPHENOLS FOR GASTROINTESTINAL CARCINOGENESIS

BACKGROUND. Recently, an epidemiologic study showed a lower risk of ga strointestinal carcinogenesis in green tea drinkers. An experiment on two-stage skin carcinogenesis in mice showed that (-)-epigallocatechin gallate (EGCG), one of the main constituents of green tea, inhibited tumor formation. METHODS. The inhibitory effects of EGCG and green tea extract (GTE) on N-ethyl-N'-nitro-N-nitrosoguanidine (ENNG)-induced d uodenal carcinogenesis in the mouse, N-methyl-N'-nitro-N-nitrosoguanid ine (MNNG)-induced carcinogenesis of the glandular stomach in the rat, and azoxymethane-induced colon carcinogenesis in the rat were examine d. The toxicity of GTE was assessed experimentally and GTE was applied clinically in normal volunteers to determine the effective dose and t o assess its harmful effects. RESULTS. EGCG and GTE inhibited chemical carcinogenesis of the gastrointestinal tract in rodents. Judging from the epidemiologic and experimental findings, it was determined that 1 g per day of GTE might be an effective dose. GTE was not toxic and no harmful effect was found during its clinical use. CONCLUSIONS. These findings suggest that EGCG and GTE are useful in preventing gastrointe stinal carcinogenesis, and the clinical usefulness of GTE, which has n o harmful effects and is inexpensive, should be studied further. (C) 1 996 American Cancer Society.