Organic Dark Chocolate
It's High Time For Tea
Published in Nutrition Science News, Understanding Herbs; April 1999
by Cindy L.A. Jones, Ph.D.
An old tradition steeped in
The tea ceremony is an important way to bind social relationships in many cultures. Although teatime is not really an American tradition, 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 chemical compounds that are rapidly absorbed and distributed throughout the body. These compounds, called polyphenols, act as antioxidants, which help protect cells from free radicals. In black tea the main polyphenols may help prevent both heart disease and cancer.2 However, green tea's main polyphenols may be even more effective than those in black tea.
Some studies suggest drinking tea protects against various cancers in humans. It is important to note, however, that cultural variables, including diet, make it difficult to determine the absolute effects of tea. And while most studies have shown positive effects of tea, others have been contradictory.
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 skin cancer melanoma and cancers of the pancreas, lung, breast, uterus and ovary.3
Another study indicated that men who drank one to six cups of tea daily had a decreased risk of developing all types of cancer. However, heavy tea drinkers (more than six cups per day) increased their overall risk of getting cancer.4 But tea scored points again in a recent Japanese study which showed that 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
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 exhibits many anticancer qualities, including the ability to inhibit the growth of cancer cells while not affecting normal cells;9 promote the death of damaged cells, or apoptosis;10 inhibit chromosomal damage;11 affect enzymes that metabolize cancer agents;11 and inhibit an enzyme associated with spreading tumors.12
Furthermore, a recent report from Japan found that green tea may also enhance the effectiveness of chemotherapy.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. Care for a spot of tea?
1. Gutman RL, Ryu B. Rediscovering tea. Herbalgram 1996;37:33-45.
2. Chemoprevention Branch and Agent Development Committee, Clinical Develop-ment Plant. Tea extracts, green tea polyphenol, epigallocatechin gallate. J Cell Biochem 1996;26S:236-57.
3. [Anonymous]. Tea drinking and cancer in women. Nutrition Research Newsletter 1996;15:104.
4. [Anonymous]. Tea and cancer. Nutrition Research Newsletter 1997 Feb;16:19-20.
5. Nakachi K, et al. Influence of drinking green tea on breast cancer malignancy among Japanese patients. Jpn J Cancer Res 1998;89:254-61.
6. Chung FL, et al. Inhibition of lung carcinogenesis by black tea in Fischer rats treated with tobacco-specific carcinogen: caffeine as an important constituent. Cancer Res 1998;58:4096-5101.
7. Huang M, et al. Effects of tea, decaffeinated tea, and caffeine on UVB light-induced complete carcinogenesis in SKH-1 mice: demonstration of caffeine as a biologically important constituent of tea. Cancer Res 1997;57:2623-9.
8. Weisburger JH. Tea and health: a historical perspective. Cancer Lett 1997;114:315-7.
9. Chen ZP, et al. Green tea epigallocatechin gallate shows a pronounced growth inhibitory effect on cancerous cells but not on their normal counterparts. Cancer Lett 1998;129:173-9.
10. Yang GY, et al. Inhibition of growth and induction of apoptosis in human cancer cell lines by tea polyphenols. Carcinogenesis 1998;19:611-6.
11. Katiyar SK, Mukhtar H. Tea antioxidants in cancer chemoprevention. J Cell Biochem 1997;S27:59-67.
12. Jankun J, et al. Why drinking green tea could prevent cancer. Nature 1997;387:561.
13. Sadzuka Y, et al. Modulation of cancer chemotherapy by green tea. Clin Cancer Res 1998;4:153-6.
14. Ishikawa T, et al. Effect of tea flavonoid supplementation on the susceptibility of low-density lipoprotein to oxidative modification. Am J Clin Nutr 1997;66:261-6.
Cindy L.A. Jones, Ph.D., is a consultant and biology instructor in Colorado.