Green tea prevents cancer

[ English Top Page ][ Green tea prevents cancer ] [ Green tea restricts the increase of blood cholesterol ] [ Green tea controls high blood pressure ] [ Green tea lowers the blood sugar level ] [ Green tea suppresses aging ] [ Green tea refreshes the body ] [ Green tea deters food poisoning ] [ Green tea stops cavities ] [ Green tea fights virus ] [ Green tea acts as a functional food ]

　

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, in Shizuoka Prefecture. This fact stimulated our interest in cancer prevention and led us to calculate the death rate (Standardized Mortality Ratio) by 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 group receiving green tea (Table 2). 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 forestsomach. 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% (Table 3). 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)

Table 2
Inhibitory Effect of Crude Green Tea Extracts on the Growth of Mouse Sarcoma 180 Tumor

	Dose (mg/kg/day)	Average Tumor Weight a) (g)	Inhibition Ratio (%)
Control Extracts Mitomycin C	- 200 p.o. x 4 400 p.o. x 4 800 p.o. x 4 2 i.p.x 4	2.04+-0.82 1.85+-1.34 1.02+-0.20 0.82+-0.55 0.37+-0.20	- 9.3 50.0 b) 59.8 c) 81.9 c)

a) The means +- S.E. b) p<0.05 c) p<0.01

The crude extacts of green tea leaves were daily administered to ICR mice orally for 4 days after subeutaneous inoculation of sarcoma 180 cells(1x107 cells/mouse).
Mitomyein C was used as a positive control. Tumor weight was compared with that of the control (10 mice/group) on the 21st day after inoculation.

Table 3
Inhibitory Effect of Green Tea Extract on the Induction of Tumors in Mice by in vivo Formation of Nitrososarcosine from its Precursors, Sarcosine and Sodium nitrite

Group

Treatment

No. of
Mice

Incidence of
Esophageal
Papilloma(%)

Incidence of Carcinonia(%)

Esophagus

Forestomach

Total

Sarcosine
+
NaNO2

GTE
+
Sarcosine
+
NaNO2

33(70.2)

20(44.4) a)

19 (40.4)

8 ( 17.8) a)

a) p<0.05 GTE : Green Tea Extract

Green tea extract(5mg/mouse/day)was intubated to mice (Tientsin II, female)6 times a week, for 14 weeks. From the second week, mice of both Group I and II were intubated with sarcosine ethyl ester hydrochloride (2g/kg) and sodium nitrite (0.3g/kg) 3 times a week, for total 5 weeks. The animals were sacrificed at the 14th week.

      From our previous epidemiological research we can estimate that the inhabitants of the mid western region of Shizuoka Prefecture, where green tea is the staple product and the main beverage, consume as much as 1.0 - 1.5g 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, Metabolism and Disease,29,453, (1992).

4) I. Oguni et al., Agric. Biol. Chem.,52,1879 (1988).

5) I. Oguni and ShuJun Cheng, Annual Retort of The Skylark Food Science Institute, No.3,57 (1991).

6) Y.Nakamura et al., Proc. of International Tea-Quality-Human Health SymPosium,pp.227-238 (Hangzhou,China,November,1087).

BACK TO ENGLISH HOME BACK TO JAPANESE HOME

Green tea prevents cancer

Table 2
Inhibitory Effect of Crude Green Tea Extracts on the Growth of Mouse Sarcoma 180 Tumor

Table 3
Inhibitory Effect of Green Tea Extract on the Induction of Tumors in Mice by in vivo Formation of Nitrososarcosine from its Precursors, Sarcosine and Sodium nitrite

Green tea prevents cancer

Table 2 Inhibitory Effect of Crude Green Tea Extracts on the Growth of Mouse Sarcoma 180 Tumor

Table 3 Inhibitory Effect of Green Tea Extract on the Induction of Tumors in Mice by in vivo Formation of Nitrososarcosine from its Precursors, Sarcosine and Sodium nitrite

Table 2
Inhibitory Effect of Crude Green Tea Extracts on the Growth of Mouse Sarcoma 180 Tumor

Table 3
Inhibitory Effect of Green Tea Extract on the Induction of Tumors in Mice by in vivo Formation of Nitrososarcosine from its Precursors, Sarcosine and Sodium nitrite