There are many benefits of drinking green tea, a powerful antioxidant. Read on to learn what studies have found regarding how this delicious brew can benefit cardiovascular health, naturally fight bacteria and help prevent cancer.
In the wild, tea plants can grow as high as 15 feet; in cultivation, the plants are kept trimmed, as these are at this Japanese tea plantation
To put the history of tea on a time line, you’d have to use a sheet of paper wide enough to let your pen trace back more than 4,000 years. And you’d want to leave plenty of room for the years ahead, if medical inquiry into this plant continues at its current pace.
Tea—specifically green tea—is drawing attention from medical researchers seeking treatments for ailments ranging from acne to heart disease, to name just two. While definitive conclusions of this research are still being formed, it appears that—at the least—there are many benefits of drinking green tea. Green tea is a powerful antioxidant to be considered seriously in terms of disease prevention.
Tea was discovered, the story goes, by a Chinese emperor living in about 2700 B.C. As he sat in the shade of a wild tea plant, a few leaves fell into his cup of hot water. He took a sip, and the rest is delicious history.
Historians trace tea’s first use to China in the twenty-eighth century B.C., but written references to it don’t appear until the third century b.c. The Chinese gathered tea leaves from wild plants until A.D. 600, when they began cultivation to satisfy demand for it—tea had become a popular medicinal tonic and beverage. Those associated with the tea trade prospered, including manufacturers of exquisite tea ware.
In about A.D. 800, a Buddhist monk studying in China took some seeds of a tea plant home with him to Japan, where cultivation of the plant soon began. Buddhists drank tea to stay awake during meditation and, in the twelfth century, the Japanese combined Buddhist beliefs and tea drinking into a ceremony of spiritual rejuvenation and harmony with the universe (the Japanese Tea Ceremony is still practiced today). Europeans trading in the China Sea discovered tea in the seventeenth century, and by the late 1700s it was widely consumed throughout Europe.
Today, tea is the second most consumed beverage in the world (water is first). About 2.5 million tons of tea leaves are produced annually, according to the University of Texas Center for Alternative Medicine Research in Cancer. Green tea is most popular in Japan and China, where its consumption accounts for about a fifth of all tea consumed worldwide.
Tea’s many names represent the country of origin (Ceylon, for example, today known as Sri Lanka), the district (such as Darjeeling), the grade or size of the processed leaf (pekoe), or the manufacturing process (green tea is unfermented, oolong is semi-fermented, and black tea is fermented). India is the world’s largest tea grower, producing 672 million pounds a year; China produces 600 million pounds, of which only 70 million are exported.
It may be helpful to know that black and green tea come from the leaves of the same plant—Camellia sinensis. The difference between the two teas lie in the processing method.
Black tea, the kind most Americans drink, has some health benefits, but green tea holds even more. Research shows that the processing of black tea—leaves are “sweated,” or fermented, to darken the leaves and produce flavor—destroys some of the beneficial health consitutuents that survive in unfermented green tea. Because 80 percent of tea consumed worldwide is black tea, however, research into green tea’s benefits is fairly new, according to the National Cancer Institute.
When looking for chemicals that may help people fight disease, researchers often turn to plants, whose constituents, including polyphenols such as catechins and flavonoids, can potentially offer humans a wide range of health benefits. Studies show that the polyphenols in green tea—including one known as EGCG—are strong antioxidants, meaning they prevent cell damage that can otherwise lead to disease.
But just how they work and whether they will work in all humans is unknown. The scientific reports focusing on green tea’s potential to protect and/or fight against disease could fill volumes. Many of these studies are precise explorations of individual compounds within the tea, and others attempt to reach a final verdict based on the research gathered so far. Some call for more study before conclusions are drawn.
However, some landmark research stands out. It’s piqued the interest of the University of Texas Center for Alternative Medicine Research in Cancer, where a clinical study is under way to get a better understanding of green tea’s health benefits. The center is focusing on only ten herbal agents that show potential for preventing cancer, a selection based not only on research findings to date, but also on public interest, says Nancy Russell, assistant epidemiologist at the Texas center.
One reason green tea is on the center’s “top ten” list, Russell says, is a report known as the “Shanghai study,” a large-scale investigation by Columbia University and the Shanghai Cancer Institute, with the U.S. National Cancer Institute participating. That study shows that people who drink green tea once a week for six months or more have a reduced risk for rectal, colon, and pancreatic cancers, and that this reduced risk may be stronger for women than men.
The researchers, who conducted the study from 1990 to 1993 and reported their findings in 1997, note that green tea might provide protection specifically from gastrointestinal tract cancers. But they caution that further studies are needed to establish the real degree of reduced cancer risk and to discover how tea works to provide it.
Russell adds that, while this study has been pivotal in the center’s current effort to learn more about green tea and cancer prevention, many other studies add to the intrigue. Among them:
Green Tea and Cancer Protection
• Researchers from the National Cancer Institute and the Shanghai Cancer Institute reported in 1994 that Chinese men and women who drink a cup of green tea a week have up to 60 percent lower risk of developing esophageal cancer. They studied a total of 902 patients with cancer of the esophagus for two-and-a-half years. They interviewed the patients along with 1,552 people without the disease (the researchers’ control group) about their medical history, smoking habits, tea consumption, and other factors.
The study also shows that the temperature of the tea is important. In fact, people who drink burning hot tea and other liquids have a fivefold increase in esophageal cancer over those who don’t. The National Cancer Institute reports that studies in China and other countries have shown that such repeated thermal irritation of the esophagus may increase esophageal cancer risk.
• EGCG (its long name is epigallocatechin-3 gallate) killed cancer cells in laboratory experiments, according to a 1997 report from researchers at Case Western Reserve University in Cleveland, Ohio. They say that there are EGCG benefits: EGCG “warns” cancer cells to die off or be killed, so the cancer cells “commit suicide”—an event known in the scientific world as apoptosis. Meanwhile, healthy cells are left unharmed.
The researchers tested EGCG on both animal and human cancer samples of skin, the lymph system, and prostate tissue. They found that one cup of green tea contains between 100 mg and 200 mg of EGCG, and suggest that drinking four cups of green tea a day should provide protection from cancer.
• Last June, researchers at the Medical College of Ohio in Toledo said they had verified that green tea’s cancer-preventing abilities come from EGCG. They found that this chemical inhibits urokinase, an enzyme crucial for cancer growth. EGCG attaches to urokinase and prevents it from invading cells and forming tumors, according to the researchers.
• By 1997, scientists at the University of Texas Center for Alternative Medicine Research in Cancer had reviewed fifteen studies on green tea’s effects on humans. Eight of these studies showed that drinking green tea protects against development of esophageal, stomach, lung, colorectal, bladder, gastric, and pancreatic cancers. But two of the studies found the opposite, with one reporting an increased risk of death from pancreatic cancer if more than five cups of green tea are consumed daily.
Skin Cancer Research and Green Tea
• In animal tests conducted by the American Health Foundation and Rutgers University, researchers found that mice who consume tea are at less risk for skin cancer than those who don’t, that caffeine may have something to do with it, and that green tea is somewhat more effective than black tea.
The researchers gave groups of mice green tea, black tea, and decaffeinated versions of both types, each prepared much the same way you and I would prepare them. They also gave one group a liquid solution containing only caffeine. For two weeks, the mice had no other source of liquid. They were then exposed to ultraviolet (UV) light.
The mice drinking green tea had up to 94 percent fewer tumors per mouse compared to the control group, which received none of the solutions before UV exposure. But the mice drinking decaffeinated green tea had about as many tumors as the control group. Mice drinking black tea had 65 percent fewer tumors and, again, the decaffeinated tea had little or no effect. Those who drank the caffeine solution, prepared at a concentration comparable to the caffeine in the tea, had 53 percent fewer tumors.
The researchers also tested whether green tea protects against skin cancer when applied directly to the skin. After exposing mice to UV light, researchers immediately applied a caffeinated green tea extract to the backs of the mice twice a week for thirty-five weeks. The mice who received the treatment had 69 percent fewer tumors than the control group.
Cardiovascular Health and Green Tea
• Researchers at Monash University in Australia reported in 1997 that Chinese and Japanese green tea prevents the oxidation of low-density lipoprotein (LDL) better than vitamin C. Oxidation of LDL plays a critical role in the development of arteriosclerosis and heart disease.
The researchers compared how equivalent concentrations of green tea, vitamin C, and vitamin E protected LDL against oxidation in a test tube. Vitamin C increased the time it took for oxidation to begin from 79 minutes to 95 minutes; vitamin E from 79 minutes to 213 minutes; and green tea from 79 minutes to 211 minutes. The researchers suggest drinking one cup of green tea daily for these benefits.
• Researchers in Japan studied 1,371 men who drank green tea daily. The researchers asked the men about their living habits, including their daily tea consumption, then analyzed samples of their blood. Based on measurements of cholesterol, triglycerides, high-density lipoprotein, low-density lipoprotein, and other factors, the researchers conclude that green tea may protect against cardiovascular disease, as well as liver disorders.
• University of Kansas researchers reported in 1997 that, by their measurements, green tea is 100 times more effective than vitamin C and 25 times better than vitamin E at protecting cells from damage linked to cancer, heart disease, and other illnesses. They also found the EGCG is twice as powerful as resveratrol, another powerful antioxidant, which is found in red wine, grapes, and other foods.
Natural Bacteria Fighters and Green Tea
• Researchers in London reported last year that both black and green tea killed a wide range of bacteria, including the antibiotic-resistant and potentially deadly Staphylococcus aureus, “at well below ‘cup of tea’ concentrations,” the researchers wrote. They attributed this to green tea’s catechins and other compounds also found in black tea.
• The volatile constituents of green tea were also shown to possess antimicrobial activity, including defense against a bacteria (Bacterium acne) that can lead to acne.
Despite the promising research on green tea, researchers at the University of Texas Center for Alternative Medicine Research advise caution before identifying green tea as the ultimate protector against serious disease. For example, they note that the effect of tea consumption on cancer is likely to depend on the causes of the specific cancer—in other words, it may work in some, but not all, instances.
“A lot of the examples we draw upon about green tea had to do with epidemiological studies—people just drinking tea over many years,” Russell says. “It may be that the positive results are showing us that green tea works to prevent cancer, but when you’ve got a full-blown case of cancer, it’s a different story.”
But based on her evaluations of the research, Russell drinks one cup of green tea a day—to keep disease away.
Pouring hot water on green tea releases its healthful constituents and flavor. Make sure to use hot, but not boiling, water—centuries of tea brewing have shown that hot water (158 degrees to 203 degrees) is better than boiling to bring out green tea’s flavor, and recent research shows that drinking boiling hot liquid may be harmful to the esophagus. Also, one study shows that adding milk to tea negates its health benefits.
• 1 teaspoon of loose-leaf green tea per cup
• 1 cup of water per serving, plus a little extra
1. Fill a kettle with cold water. Bring the water to a near boil, then pour a little into a teapot to warm the pot, swirl it around, and discard the water.
2. Put the tea directly into the pot or use a teaball. One teaspoon per person is the general recommendation, but adjust the amount of tea to taste. Fill the pot with the near-boiling water. Put the lid on the pot and infuse for 10 minutes before serving in individual cups.
Black tea: Tea leaves that have been fully fermented or oxidized. Darjeeling is a black tea.
Ceylon: Black tea harvested in Sri Lanka.
Darjeeling: Tea harvested in the Darjeeling district of India.
Green tea: Tea leaves that are unfermented.
Gunpowder: A type of green tea from China. The leaves are rolled into fine pellets that unfold in water.
Herbal tea: Tea made from herbs other than Camellia sinensis, such as chamomile and peppermint teas.
Infusion: Another word for tea. A French word sometimes used in English-speaking countries is tisane, which means infusion.
Oolong: Partially fermented tea.
Pekoe: Whole-leaf black tea that has been flavored, such as orange pekoe.
Jan Knight is editor of Herbs for Health. Kenneth Jones of British Columbia, and Cindy L. A. Jones, Ph.D., of Colorado, both frequent contributors to Herbs for Health, provided research support for this article.
To learn more about green tea’s health benefits and history, an article by Robert Gutman and Beung-Ho Ryu, “Rediscovering Tea,” in the summer 1996 issue of HerbalGram (a publication of the American Botanical Council) provides a concise description of the history of green tea and scientific findings up to 1996.
For more about its history and the art of tea drinking, as well as descriptions of the many varieties of tea and their processing, you may wish to read The Tea Companion (New York: Macmillan, 1997) by Jan Pettigrew with Mariage Frères. A hardbound, pocket-sized book, it lets you relish the rich history of tea while offering ways to carry tradition into the present. (Extensive medical information is not included in this book.)
The University of Texas Center for Alternative Medicine Research in Cancer has a website: http://chprd.sph.uth.tmc. edu/utcam/
Ahmad, N., et al. “Green tea constituent epigallocatechin-3-gallate and induction of apoptosis and cell cycle arrest in human carcinoma cells.” Journal of the National Cancer Institute 1997, 89(24):1881–1886.
Imai, K., and K. Nakchi. “Cross sectional study of effects of drinking green tea on cardiovascular and liver disease.” British Medical Journal 1995, 310(6981):693–696.
Ji, B. T., et al. “Green tea consumption and the risk of pancreatic and colorectal cancers.” International Journal of Cancer 1997, 70:255–258.
Luo, M., et al. “Inhibition of LDL oxidation by green tea extract.” The Lancet 1997, 349:360–361.
Snow, Joanne. “Herbal Monograph: Camellia sinensis (L.) Kuntze (Theaceae).” The Protocol Journal of Botanical Medicine 1995, 1:47–51.
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