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The Science Behind the Beverage

One of the key factors driving this expanding interest in tea is the health news about green tea. Scientists have studied the effects of green tea and its chemical compounds extensively, especially the polyphenols, or tea tannins. Polyphenols, which are recognized by many researchers as the principal health-promoting ingredients in green tea, are anticarcinogenic, protect lipids from oxidation, and have antibacterial and antiviral action, according to Robert Gutman, Ph.D., and Beung-Ho Ryu, Ph.D. (Herbal-gram, 1996, no.37).

Researchers found that the phenol epigallocatechin gallate (EGCG) reduced rates of skin, lung and stomach cancers in mice subjected to carcinogens. One study concluded that mice that ingested a daily dose of EGCG equal to four to six cups in humans had 70 percent fewer stomach tumors and 55 percent fewer lung tumors than the control group (Preventive Medicine, vol.21).

The results of human research are less clear. Yet, recent studies suggest tea drinking may reduce risk of esophageal cancer in women living in Shanghai (Journal of the National Cancer Institute, 1994, vol.86); mouth cancer in Northern Italians (Cancer, 1992, vol.70); gastric cancer among Swedish adolescents (International Journal of Cancer, 1993, vol.55); as well as pancreatic cancer among the elderly of Poland and the United States (International Journal of Cancer, 1994, vols. 53 and 58). Researchers comment that these recent studies may still be said to be inconsistent and inconclusive, but most now conclude that tea is a chemopreventive (a food used to prevent abnormal tissue formation) in humans.

The late Herb Piersen, Ph.D., former director of the National Cancer Institute's Designer Foods Program, worked for years to identify potent anticancer compounds that could be increased in the American diet and possibly reduce overall cancer risk. Of many important studies he cited on a vast array of plant constituents, the studies on green tea are among the most fascinating. Piersen reported at the 1994 Nutracon Conference on nutraceuticals that tea can help reduce breast cancer risk. A woman's liver metabolizes and excretes estrogen through the gall bladder into the bile. But bacteria in the intestines change estrogen waste by-products into an even more potent and cancer-promoting hormone, which is reabsorbed through the intestines. Tea stops the bacteria from creating this dangerous reaction (Nutracon conference managers: Global Business Research, New York).

Green tea also exhibits antioxidant properties. One study shows it reduces, if not prevents, ultraviolet B (UVB)-induced inflammatory responses and depletion of epidermal antioxidant defenses (Cancer Causes Control, 1992, vol.3). The antioxidant benefits associated with tea polyphenols are generally attributed to their ability to scavenge free radical oxygen molecules that can cause tissue damage and lead to disease. Upon ingestion, concentrations of tea polyphenols can be detected in blood, urine and feces. Thus, they're absorbed through the human body. Their actions probably occur directly at the tissue and cellular levels rather than indirectly through the intestines (Plant Foods for Human Nutrition, vol.46).

  In addition to their anticarcinogenic and antioxidative abilities, green tea phenols appear to reduce hypertension in mice, perhaps through the sedative action of the brain neurotransmitter gammaaminohutyric acid. Also, the antibacterial activity of tea compounds is useful for treating diarrheal diseases such as cholera and typhus (Journal of Communicable Diseases, 1994, vol.26). These compounds may also help prevent tooth decay by killing the causative bacteria (Journal of Endodontics, 1991, vol.17) or by increasing the acid resistance of human tooth enamel (Journal of Dentistry, 1995, vol. 23). As an antiviral, green tea has been shown to adversely affect the presence of viruses including influenza and even HIV (Biochemistry, 1990, vol.29).  Drink to a Healthy Heart Green tea has also shown protective effects for the heart in recent scientific research. For example, clinical research demonstrated that green tea was associated with lowered serum cholesterol and triglyceride levels and with improved LDLIHDL ratios (British Medical Journal, March 18,1995). Most people are unaware that the heart-protective effects of green tea are shared by black and oolong teas as well. Since the 1960s research has consistently pointed to tea as a more healthful hot beverage than coffee. In studies using water as a neutral control, coffee increases blood fat levels, while tea actually reduces them (Nature, vol.214). Researchers also report that in a test-tube study of 39 food-derived antioxidants, the phenols in tea proved the most potent inhibitors of LDL oxidation, a contributor to heart disease. In fact, one compound was 20 times stronger than vitamin C, a potent antioxidant (Journal of Agricultural and Food Chemistry, 1995).

Because of the publicity resulting from tea research, tea and its extracts have found their way into other products, too. Green tea extracts are becoming common in dietary supplements and are available in caffeinated and decaffeinated versions. Since the antioxidant effects don't rely on caffeine, both can offer health benefits. Apparently caffeine is unrelated to cardioprotective effects, too, since neither coffee nor caffeine itself provides the same effects offered by tea.

Rob McCaleb is president of the Herb Research Foundation in Boulder, Cob., a nonprofit organization dedicated to bettering world health through herbs. For more herb information, call 800-748-2617 Or; Visit http://www.herbs.org on the Web.

 

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