2006 年 52 巻 3 号 p. 211-220
The effects of repeatedly brewed green tea infusion on the formation of nitrosamine in vitro and in vivo, and on cancer mortality were examined. The first and second brews of green tea infusion inhibited the formation of nitrosomorpholine in the presence of morpholine and nitrite (nitrosation of morpholine), but the third to eighth brews accelerated it. The green tea infusion brewed from 5 g of leaves in 200 ml hot water (strong tea infusion) inhibited the nitrosation of morpholine, but that brewed from 2.5 g or less (weak tea infusion) promoted the nitrosation. The brewed green tea infusion that inhibited nitrosation of morpholine contained catechins at a high concentration, and that that promoted nitrosation contained catechins at a low concentration. The effects of green tea administered to Wistar male rats and that consumed by humans on the formation of nitrosamines were also examined. In both rats and humans, nitrosamine formation was inhibited by strong green tea extract but was increased by weak green tea extract. The concentration of catechins in the green tea infusion brewed by the general households in tea-producing areas was significantly higher than that brewed in non-producing areas. We examined the relationship between the concentration of catechins in green tea infusion brewed in different areas and the standardized mortality ratio (SMR) of cancer in respective areas, and found that the catechin concentration in green tea infusion correlated inversely and significantly with the SMR of cancer in that area. We concluded that strong green tea might inhibit the formation of nitrosamines and decrease the risk of carcinogenesis.
