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PROTECTIVE FACTORS AGAINST CANCER IN TEA (CAMELLIA SINENSIS)
Epidemiological studies
show a reduced cancer incidence in regions of high tea consumption (OGUNI,
1992). By in vitro experiments NAKAMURA (1992) could prove that there is an
inhibitory effect at the neoplastic transformation of murine cell cultures by
tea extracts and that this effect is stronger for green than for black tea
extracts. He observed also that next to the low molecular catechin fraction
higher molecular, non-dialysable components are effective. In the catechin
fraction it is mainly (-)Epigallocatechin-Gallate (EGCG) and
(-)Epicatechin-Gallate (EGC) which inhibit (OSAWA, 1992). XU (1992) compared
the effect of a 2% tea infusion, of 560 ppm EDCG in water, 1120 ppm caffein in
water and pure drinking water on mice with induced tumors. The tumor
multiplicity (average number of tumors per mouse) was reduced by the tea
infusion by 45%, by the EGCG by 30% and by the caffein only moderately but
still significantly in comparison with the control group on pure drinking
water. TAO SHI (1994) found that EGCG is a potent inhibitor of
4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone oxidation and DNA methylation in
vitro. Green and black tea extracts did, however, in vivo not reduce lung DNA
methylation but did reduce induced lung tumor multipicity. The polyphenols of
green tea (EGCG, ECG, Theaflavines) do at the same time also lower the
cholesterol level and the blood pressure. They also seem to inhibit the
activity of the alpha-amylase (HARA, 1992) which could explain the reduced
weight gain of mice to whom tea and caffein was administered (XU, 1992). WANG
(1992) reports that the extract of green tea inhibits the formation of skin
tumors of mice after UVB irradiation and administration of
12-O-Tetradecanoylphorbol-13-acetate. Number and size of tumors induced by UVB
irradiation and administration of 7,12-Dimethylbenzanthracen was diminished by
green tea extracts.
References
HARA, Y. et al., 1992: The
Effects of Tea Polyphenols on Cardiovascular Diseases. Preventive Medicine 21,
333
NAKAMURA, Y. et al. 1992:
Inhibition of in Vitro Neoplastic Transformation by Tea Ingredients. Preventive
Medicine 21, 332
OGUNI, I. et al., 1992:
Protection against Cancer Risk by Japanese Green Tea. Preventive Medicine 21,
332
OSAWA, T. et al., 1992: Tea
Polyphenols as Antioxidants. Preventive Medicine 21, 331
TAO SHI, ST. et al., 1994:
Effects of Green Tea and Black Tea on
4-(Methylnitrosamino)-1-(3-Pyridyl)-1-butanone bioactivation. Cancer Research
54, 4641-4647, September 1, 1994
WANG, Zh.J. et al., 1992:
Inhibitory effect of Green Tea in the Drinking Water on Tumorigenesis by
Ultraviolet Light and 12-O-Tetradecanoylphorbol-13-acetate in the Skin of SKH-1
Mice. Cancer Res. 52, 1162-1170, March 1, 1992
XU, Y. et al., 1992: Effects of Green Tea and Its Components on Lungtumorigenesis Induced by a Tobacco-Specific Nitrosamine. Preventive Medicine 21, 331
