Tea Steeped in Anticancer Properties

[Guest guest]

By Cindy L. A. Jones

Thursday, April 04, 2002

http://www.authorsden.com/visit/viewarticle.asp?AuthorID=5357 & id=5002

 

Tea used to be the favored drink of Americans. With new evidence of its health

promoting effects, many Americans are again drinking tea. Components of tea have

particularly been found to have anti-cancer effects.

 

 

Tea: Steeped in Anticancer Properties

By Cindy L.A. Jones, Ph.D.

The tea ceremony is an important way to bind social relationships in many

cultures. Although Americans have not traditionally partaken in this ritual, tea

consumption here is increasing, possibly due to its health benefits.

Almost any drink made by adding hot water to leaves, flowers or roots can be

called tea, but traditionally tea is made from the leaves and buds of the

Camellia sinensis bush, grown primarily in India.

Three types of tea are derived from C. sinensis. The differences stem from how

the tea leaves are handled after harvesting. The majority of tea produced is

black tea, made by fermenting the leaves. Oolong tea is partially fermented tea,

whereas green tea leaves are not fermented but simply dried or steamed. Green

tea is most popular in southeastern China and Japan and is used there

medicinally as a stimulant and a digestive aid.1

All these teas contain polyphenols, chemical compounds rapidly absorbed and

distributed throughout the body that act as antioxidants. In black tea the main

polyphenols are theaflavins and thearubigins, antioxidants that may help prevent

both heart disease and cancer.2 In green tea the main polyphenols are the

catechins epigallocatechin-3-gallate and epicathechin-3-gallate. Studies show

the antioxidant compounds in green tea may have more of an effect than those in

black tea.

Potent Antioxidants

Epidemiological studies suggest drinking tea protects against various cancers in

humans, although evidence is contradictory. Some problems with studies are

cultural variables, including diet, that make it difficult to determine the

absolute effects of tea.

The Iowa Women's Health Study, which looked at 35,369 postmenopausal women,

showed those who drank two or more cups of black tea per day had a decreased

risk of digestive and urinary tract cancers. However, other cancers were not

affected, including the skin cancer melanoma and cancers of the pancreas, lung,

breast, uterus and ovary.3 The postmenopausal angle is important because many

cancers, particularly breast and ovarian, are hormone-dependent cancers, and

hormonal changes at menopause change the risk ratios for different types of

cancer.

Another study indicated that men who drank one to six cups of tea daily had a

decreased risk of developing all types of cancer, while heavy tea drinkers (more

than six cups per day) increased their overall risk of getting cancer.4 A recent

Japanese study showed 472 women with breast cancer who regularly drank green tea

prior to diagnosis had less severe cases than women who did not drink green

tea.5 The most inconclusive results on the effects of tea are for stomach and

colon cancer; some studies show increased risk, others show decreased risk, and

still others show no association whatsoever between drinking tea and developing

cancer.4 These discrepancies may be due to the inherent drawbacks of

epidemiological studies.

On the other hand, animal and other preclinical laboratory studies suggest that

both green and black tea (oolong is the least consumed and studied) decrease the

risk of several cancers. Studies regarding tea's effect on lung cancer in humans

are inconclusive, but animal studies suggest tea may inhibit tobacco-induced

cancers.6

One 1997 animal study showed that green or black tea applied to the skin

inhibited ultraviolet light-induced skin cancer in mice. When decaffeinated

green or black tea was administered, however, tumor formation was not inhibited.

This indicates, interestingly, that caffeine may be another medicinally active

ingredient of tea.7 Other animal studies indicate that tea might help prevent

lung, stomach and esophageal cancers.8

In test-tube experiments, tea polyphenols exhibit many anticancer qualities,

including the ability to inhibit the growth of cancer cells while not affecting

normal cells;9 promote apoptosis, or cell death of damaged cells;10 inhibit

chromosomal damage;11 affect enzymes that metabolize cancer agents;11 and

inhibit an enzyme associated with tumor metastasis called urokinase-type

plasminogen activator.12

A Japanese group that green tea may enhance the effectiveness of chemotherapy.

Chemotherapy typically has side effects, and anything that can decrease the

amount of drug administered while maintaining a tumor-inhibiting effect would

most likely improve the quality of life for cancer patients. When green tea and

doxorubicin--a cancer treatment drug that prevents the development, growth and

proliferation of malignant cells--were given together to mice with cancer, the

inhibitory effect of doxorubicin was enhanced 2.5-fold.13

Tea may prove to be more than a pleasant afternoon ritual, but do avoid overhot

tea. Overhot tea--and perhaps all overhot drinks--has been associated with a

greater risk of developing esophageal cancer, and as mentioned, drinking more

than six cups of tea daily has been associated with an increased cancer risk.

From The March 1999 Issue of Nutrition Science News

Understanding Herbs

Cindy L.A. Jones, Ph.D. is a consultant, biomedical writer and biology

instructor in Colorado.

References

1.Gutman RL, Ryu B. Herbalgram 1996;37:33-45.

2.Chemoprevention Branch and Agent Development Committee, Clinical Development

Plant. J Cell Biochem 1996;26S:236-57.

3.[Anonymous]. Nutrition Research Newsletter 1996;15:104.

4.[Anonymous].Nutrition Research Newsletter 1997 Feb;16:19-20.

5.Nakachi K, et al. Jpn J Cancer Res 1998;89:254-61.

6.Chung FL, et al. Cancer Res 1998;58:4096-5101.

7.Huang M, et al. Cancer Res 1997;57:2623-9.

8.Weisburger JH. Cancer Lett 1997;114:315-7.

9.Chen ZP, et al. Cancer Lett 1998;129:173-9.

10. Yang GY, et al. Carcinogenesis 1998;19:611-6.

11.Katiyar SK, Mukhtar H. J Cell Biochem 1997;S27:59-67.

12.Jankun J, et al. Nature 1997;387:561.

13.Sadzuka Y, et al. Clin Cancer Res 1998;4:153-6.

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