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Green Tea Prevents Cancer
Cancer mortality statistics on Japanese people indicate that the death rate from
cancer is significantly lower, for both men and women, i Shizuoka Prefecture.
This fact stimulated our interest in cancer prevention 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.(#2)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.(#2,3) 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 (#4)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%. (#5)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.(#3)
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(#6)
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.
(#2)I.Oguni et al., Japanese J. of Nutrition, 47, 31 (1989).
(#3)I.Oguni, Metabolzsm and Disease, 29, 453, (1992).
(#4)I.Oguni et al.Biol.Chem,52,1879(1988)
(#5)I.Oguni and ShuJun Cheng,Annual Report of the Skylark Food Science
Institute,No 3,57(1991)
(#6)Y.NAKAMURA etal,PROC.ofInternatiomal Tea-Quality-Human Health Symposium,pp.227-238(Hangzhou,china,November,1987)
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