The Qi of Tea
Author: Dr. Zhi Yuan Wang
Tea, a traditional product of China, has become one of the world's three major kinds of non-alcoholic drinks. In fact, tea is presently consumed in a larger area worldwide than coffee or coca, the other popular beverages. Why did the habit of tea drinking spread from China to every corner of the world? The answer lies with its health-promoting properties.
That tea drinking can benefit us both mentally and physically is frequently mentioned in ancient Chinese books. In Shennong's Herbal, it is said that "Habitual drinking can ease one's mind and benefit one's Qi (vital energy)...increase one's stamina and keep us fresh and young." Shennong's Treatise on Food says, "The habit of drinking tea brings vitality and a pleasant state of mind." Hua Tuo's Treatise on Food also records that "Drinking tea gives one a clear mind." These books were written in the Western Han Dynasty (206 B.C. to 8 A.D.) and the Eastern Han Dynasty (25 A.D. to 220 A.D.)
Later on, it was discovered that drinking tea not only strengthens the body but also cures certain diseases. For example, in the Tang Dynasty (618 A.D. to 907 A.D.), in Lu Yu's The Treatise on Tea said, "Tea is cold in taste and is most suited for drinking...If one is thirsty or has a headache, tired eyes, restlessness of four limbs, and uncomfortable joints, then a few sips of tea can be as good as manna." In the Ming Dynasty (1368 A.D. to 1611 A.D.), Zhang Qiande, author of a book also called A Treatise on Tea says, "Drinking tea slakes thirst, aids digestion, keeps off diseases, shortens the time for sleeping, relieves water retention, improves eye sight, brings clear thinking and removes disturbances; humans should not stop drinking tea for even a single day."
In the past hundreds of years, many people have believed that there really are numerous advantages to drinking tea. However, until recently, this was only a kind of intuitive understanding, since there was no supporting evidence or exposition in scientific theory. With the recent advancement in science and technology, the substances that comprise tea and their benefits on human physiological mechanisms have become the subject of scientific experimentation and research; and the mystery of tea in promoting bodily health and curing diseases is gradually being unveiled.
According to chemical tests, tea is now known to contain more than 320 different kinds of chemicals. The major ones are polyphenols, caffeine, perfume oils, and various vitamins. These chemicals have certain positive effects on people's health.
The polyphenols, which amount to around 20% to 30% of the total weight of dry tea, have restraining properties, activate saliva secretion and so slake the thirst. Polyphenols lessen the toxic effects of high alcohol content in blood and alkalosis. Therefore, drinking tea can aid sobriety and reduce the effects of nicotine on smokers. Polyphenols have a strong ability to solidify proteins and, since the main constituting substance of germ cells is protein, concentrated tea can kill germs. Concentrated tea can be applied effectively instead of iodine, and it also helps to cure dysentery. Polyphenols in tea is composed of more than thirty phenolic substances of which caffeine amounts to around 7%. Consequently, the habit of drinking tea will prevent high blood pressure, arteriosclerosis, coronary heart diseases and cancer.
Pros and Cons - A Look at the Evidence
While recent studies highlight the benefits of tea, others have attributed negative effects to tea consumption. In the 1970s, it was suggested by Dr. Morton, a USA scientist, that excessive consumption of tea or tannin-containing food such as sorghum may be a causative factor for the high incidence of esophageal cancer in the esophageal cancer zone extending from Iran to Northern China. Dr. Zhi Y. Wang, a Chinese scientist, was the first one to query the validity of Dr. Morton's hypothesis. In China, most of the areas with higher esophageal cancer mortality rates are in Norther provinces, where tea is not produced and is infrequently consumed. In the high incidence area of Linxian in Northern China, consumption of tea is rare and is believed to not be a contributing factor. In such places as Turkmenistan and Northern Iran, large amounts are traditionally consumed very hot; a habit that might account in part for the elevated incidence of cancer of esophagus in those places, due to not the tea, but to the high temperature at which it is consumed.
Consumption of green tea is associated with lower risk of cancer of the stomach, esophagus, and lung in some but not all studies. For example, a population-based case-control study of esophageal cancer in urban Shanghai by Gao, et al, indicated that after accounting for cigarette smoking, alcohol drinking, dietary factors and other variables, the risk of reduction of esophageal cancer due to green tea consumption was about 20% among males and 50% among females. For non-smokers and non-alcohol drinkers, the risk of esophageal cancer were reduced by 57% for men and 60% for women due to tea consumption.
In the past 15 years, there are more and more results from laboratory studies all over the world suggesting the inhibitory effects of tea against tumorigenisis in experimental animals. In animal models for cancer of the skin, lung, esophagus, mammary glands and colon, intake of green and black tea as a sole drinking fluid lowered the incidence, multiplicity, and the volume of the induced tumors compared to animals on water. On April 26, 2997, in the news conference of "Diet and Cancer" organized by American Cancer Research Association, Dr. Zhi Y. Wang, professor of Columbia University was invited to make a statement for public release. He declared that oral administration of green tea or black tea effectively protected against chemical carcinogenesis, photocarcinogenesis, photochemical carcinogenesis, and spontaneous turmorigenesis in different animal models.
For example, rats were treated with a chemical carcinogen N-nitrosomethylbenzylamine (NMBzA) twice weekly for five weeks. Thirty-nine weeks after the initial dose of NMBzA, 65% of the rats developed tumors with an average of 1.4-0.3 tumors per rat. In groups of rats receiving 0.6% of decaffeinated green tea or decaffeinated black tea as the sole source of drinking fluid during the NMBzA treatment period, esophageal papilloma incidence and multiplicity were reduced by approximately 70%. When the tea preparations were given after NMBzA treatment period, the esophageal papilloma incidence and multiplicity were reduced by approximately 50%. The tumor size was much smaller in rats that received tea administration either during or after the carcinogen treatment period. In fact, the growth of induced mouse skin papillomas was inhibited by oral administration of green tea or by i.p. injection of green tea polyphenols. At the 88th Annual Meeting of American Cancer Research, 1999, Dr. Wang reported that both green tea and black tea induce apoptosis in human carcinoma MCF-7 cells, but not in non-carcinoma cells MCF-10. This means that the tumor suppression effect of tea may have scientific selection.
Green tea is mainly consumed in China and Japan. Black tea, a product of green tea, is predominantly consumed in Western countries other than Asian and African countries. Previously, it was assumed that the beneficial effects of green tea would be lost by oxidation of active polyphenolic ingredients during its fermentation to black tea. It is now known that during fermentation activated endogenous polyphenols oxidase enzyme(s) oxidize most of the monomeric flavanoids to yield flavanols such as theaflavis (TF) and thearubgins (TR). Both in vitro and in vivo studies showing that TFs and TRs inhibit lipid peroxidation provide evidence that the TFs adn TRs, indeed, are potent antioxidants. Similarly, a human study indicates that the oral administration of black tea reduces plasma lipid peroxide levels. In another study, the ingestion of black tea has been shown to produce a significant increase in tissue antioxidant capacity. Therefore, both green and black tea has been shown to have benefits for health.
Dr. Zhi Yuan Wang is a pioneer in the field of tea and cancer in the world. Currently he is involved in setting up the Botanicals for Health Center for American Health Foundation. He was a former research associate professor at the College of Physicians & Surgeons, Columbia University before he moved to the American Health Foundation. His research has focused on nutrition, diet, botanicals and cancer, including tea, licorice, garlic, grapes, ginseng, soy, turmeric, and rosemary. He is the author of more than 79 scientific papers and book chapters and the editor of a book about environmental toxicology.