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It's been about 20 years since academic resolution of cancer prevention by tea. Green tea extract and green tea catechins are attracting worldwide attention as the most important food functional components to prevent cancer, and further research is being continued. The efficacy of green tea against cancer is academically recognized when 3 hurdles are completed. First one is epidemiological data to show interrelation between amount of green tea and rate of cancer/death of cancer, and the second is the experimental data to back up the epidemiological data. And the third is the assurance of efficacy by human experiment and clinical testing. Currently we are in the third stage. As for epidemiological studies, there is a report to prove the interrelation of frequency of drinking green tea and death rate of stomach cancer in Shizuoka prefecture and Kita-kyushu district. The National Cancer Research Center in the United States confirmed that drinking green tea suppresses the occurrence of esophagus cancer based on the research in Shang-hai.China. However, the reports to show the efficacy of drinking tea against cancer are not enough(Fig.1), few data on black tea vs. cancer prevention. In the area of experiment, enormous data have been accumulated to support the efficacy of green tea extract and catechins against carcinogenicity by animal models and in vitro experiments. However, in animal experiments, there are reports that show amount and effect are not dependent enough and that efficacy is not constant with the amount. In multi-organs medium stage cancer model by Nagoya City University, efficacy of green tea catechins is not uniform, which still leaves a problem to solve. Anti-cancer mechanism is categorized as: 1.anti-mutagenic(initiation), 2.anti-cancer promotion, 3.anti-cancer progression, 4.anti-mutangenic increase of cancer cells(suppress increase of selected cells and Apotosis guidance, 5.anti-metastasis of cancer, and catechins are proven to be effective in each point by in vitro and animal experiments. No other food components have multi control effects as green tea, and further research to solve efficacy of molecules and gene level is being done. There are not enough data on assimilation, metabolism and excretion of animals and human beings. It is said that several % are assimilated and most are excreted but further analysis is required. Intake of green tea catechins of a person who drink 10 cups of green rtea a day is about 0.6~1.2g/person/day if it is Sencha, a little less with Bancha, and 1/2~1/3 of that of leaves if it is canned drinks. The effective amount of green tea catechins to prevent carcinogenicity of cancer is 20mg/day for 1kg of the weight of a person based on epidemiological data, 10mg based on animal experiment, and 20mg is applied on clinical testing. An appropriate amount of tea is 1.0g~1.2g for a Japanese person who weighs 50~60kg, which is about 3 big cups that is offered at Sushi bar. In human application at Saitama prefectural cancer center, it is reported that a cancer patient drinking more than 10 cups of tea a day showed the delay of cancer carcinogenicity, and that a breast cancer patient drinking more than 5 cups a day showed the lower rate of recurrence. The effect of green tea catechins and green tea extract against cancer has been studied on human applications in the United States since September of 1997. The link studies between Japanese institution of private sectors and National cancer research center in the United States, and Texas University MD Anderson Cancer Center are on the way. They are reported to have started the second stage of the experiment in summer of 2000. In the near future, green tea and green tea catechins will be added in menu to prevent cancer for people, and they will be a medicine for high cancer risk group of people.

(Yoshiyuki Nakamura)