Green tea prevents cancer

Cancer mortality statistics on Japanese people indicate that th death rate from cancer is significantly lower, for both men and women, i Shizuoka Prefecture. This fact stimulated our interest in cancer preventio and led us to calculate the death rate (Standardized Mortality Ratio) b cancer type for every city, town and village in Shizuoka Prefecture. Based on these death ratio statistics, we created a cancer distribution map of the Prefecture and examined it in detail for trends. We found that areas devoted to green tea production in the central and western regions of Shizuoka Prefecture exhibit a significantly lower death rate for all types of cancer in general and for gastrointestinal cancers such as stomach, esophagus and liver cancer in particular.We then made a survey to see how the residents of the green tea producing regions, which have such low cancer death rates, drink their tea. The results showed that those who live in areas where green tea is the staple crop tend to drink it daily in rather strong concentrations by frequently refreshing the tea leaves in their pots. From these results we theorized that green tea must be connected in some way with cancer prevention, and we decided to continue our research with animal experiments.

Mice were first inoculated with cancer cells and then studied for the growth of malignancies. One group was given an extract of green tea while another control group was not given such an extract. Comparison of the two groups showed a marked reduction in the growth of tumors among the receiving green tea.In further joint research with Prof. Shu-Jun Cheng of the Cancer Institute, Chinese Academy of Medical Science (Beijing),mice were given substances which, when transformed in the body to cancer-causing chemicals, generate carcinoma in both the esophagus and forestomach. The researchers then proceeded to check if green tea has the ability to inhibit the development of these cancers. Administration of green tea extract did indeed reduce the incidence of cancer to less than 50% .In addition, research at the National Cancer Institute (Tsukiji, Tokyo) has demonstrated that administration of catechin (the main component of green tea tannin) to mice previously given chemicals that induce duodinal cancer can also significantly lower the incidence of cancer. Green tea and its component catechin have, therefore, been shown to reduce the growth as well as the actual generation of cancer.

From our prevlous epldemiologlcal research we can estlmate that the inhabitants of the midwestern region of Shizuoka Prefecture, where green tea is the staple product and the main beverage, consume as much as 1.0 1.sg of crude green tea catechins daily in their green tea. This strongly suggests that green tea catechin plays a role in their low SMR (Standardized Mortality Ratio) for stomach cancer.

We do not yet fully understand the mechanism underlying the generation of cancer, but it involves at least the following two stages. This is called the "two-stage theory of cancer development., A substance capable of causing mutations (initiator) first damages DNA in the cell and renders it subject to cancer (initiation). This condition then remains unchanged for some time until another substance, which activates cancer (promoter),leads to the actual growth of a malignancy (promotion). It is clear from recent research that extract of green tea and catechin can markedly inhibit both stages of development.

Even though these results have been gained from animal studies or pure laboratory tests, we think it highly significant that green tea and its component catechin have the ability to prevent cancer. When taken together with the survey that indicates a striking reduction in the cancer death rate in the tea producing regions where the residents are accustomed to drinking quite strong tea by frequent changes of tea leaves, they support the conclusion that green tea may also be a factor in the prevention of human cancer.