Long cultivated in China, both black and green teas are derived from the same plant - Camellia sinensis. This plant is an evergreen shrub or tree which can grow to an incredible height of up to 30 feet. When cultivated, a typical height is 2 to 3 feet, which is attained by routine pruning. The parts used are the leaf bud and the two young leaves adjacent to the bud, together with the stem. Older leaves are not used as they are considered inferior in quality.
Green tea is obtained by lightly steaming the leaves when they are freshly cut. Black tea is produced by allowing the leaves to oxidize. During the oxidation process, enzymes present in the tea convert polyphenols, which have extensive therapeutic properties. Oxidation is not allowed to take place in the making of green tea because the steaming process inactivates many of the important enzymes. Therefore, green tea contains high polyphenol content with anti-cancer properties and potent antioxidants. Oolong tea, however, is partially oxidized.
History of Green Tea
Consumption of tea dates back more than 4,000 years to China. Since that time, teas have been used not just as beverages, but as part of traditional medicine in achieving better health and wellness. In most of Asia (including China, Vietnam, Japan, Thailand and Korea), tea has been used for ailments ranging from regulating body temperature to controlling bleeding. Teas were also used to control blood sugar and promote healthy digestion.
The first known book extolling the benefits of green tea was called Cha Jing, or “Tea Classic,” and was written between 600 and 900 A.D. The Kissa Yojoki (Book of Tea), written by a Zen priest in 1191, mentions how drinking green tea can have beneficial effects on the five vital organs. The book also describes tea’s medicinal powers for preventing fatigue, curing beriberi disease, improving brain and urinary function and eliminating indigestion.
Although nearly 2.5 million tons of tea is produced each year, only 20% of that amount is green tea. Black tea is more popular in India and Sri Lanka, while green tea is primarily produced and consumed in Japan, China, and a handful of countries in the Middle East and North Africa.
Green Tea Constituents
The major components found in green tea are polyphenols. (Polyphenol denotes the presence of several phenolic rings.) The polyphenols which are found in green tea are flavonoids, including catechin, epicatechin, epicatechin gallate, epigallocatechin gallate, and proanthocyanidins. The most significant active component is thought to be the epigallocatechin gallate. The leaf bud and the first leaves contain the highest amounts of this compound. The polyphenols in green teas are usually around 8 to 12 percent of the total concentration.
Other compounds which are found in dried green tea leaf include caffeine at about 3.5%; an amino acid called theanine, which is one-half of the total aminio acid content; lignin at 6.5 %; organic acids at 1.5%; protein at 15% and chlorophyll at .5%
However, the chemical composition found in green teas varies with the climate, the season, the horticultural practices which were used during the growing process, and the actual age of the tea leaf.
Green Tea Health Benefits
Green tea's clinical application is primarily for the prevention of cancer. Numerous studies of populations have shown that green tea consumption may be the major reason why the cancer rate in Japan is much lower than other regions of the world. These same studies indicate that black tea consumption does not have the same protective effects and may actually increase the risk for cancers such as those affecting the endometrium, the rectum and the gallbladder.
Green tea appears to be most effective in the prevention of gastrointestinal cancers, such as cancers involving the small intestine, the stomach, the pancreas and the colon, as well as lung cancer and many types of breast cancer.
Some studies have shown that green tea extracts can inhibit the growth of mammary cancer cell lines. They primarily inhibit the interaction of tumor promoters, hormones, and growth factors by having a “sealing off” effect from the cancer receptors.
When green tea is consumed with meals it may serve to inhibit the formation of nitrosamines. Nitrosamines are known to form when nitrites (such as those used in curing bacon and ham) bind to amino acids.
The custom in Japan of drinking green tea with meals is thought to be the major reason for the country's low cancer rate.
The polyphenols in green tea are also potent antioxidants and are demonstrated to have even greater antioxidant properties than those found in vitamins C and E.
Some research suggests that green tea extracts can help prevent the oxidative damage which occurs from excess exposure of the skin to UVB radiation. Drinking green tea may also help prevent skin cancer.
When consuming green tea as a "tea" for its medicinal benefits, at least three cups daily should be taken. This provides approximately 240 to 320 milligrams of polyphenols. If taking green tea extract, a daily dose of 300 to 400 milligrams is suggested. Green tea extracts can be taken orally or can be used topically.
One cup of green tea typically contains from 300 to 400 milligrams of polyphenols and around 50 to 100 milligrams of caffeine.
Green tea does not have any known significant side effects or toxicity. Any caffeine-containing beverage can cause a stimulant effect when over-consumed. This overconsumption can produce symptoms such as anxiety, insomnia, nervousness, and irritability. Typically, however, green tea does not produce these side effects, even in the case of one who is unusually sensitive to caffeine.
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