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