Camellia sinensis. Family: Theaceae
black tea, Chinese tea, Oolong tea, tea
Green tea is obtained from the plant Camellia sinensis. Black tea, green tea, and Oolong tea are all produced from varieties of the same plant. The different types of tea are created using different processing methods.
Green tea extract contains a variety of polyphenols that includes the most active polyphenol, epigallocatechin gallate. Green tea and Oolong tea have the highest levels of polyphenols, giving them the greatest health benefits. The fermentation and processing involved in creating black tea decreases the polyphenols by converting them to theaflavins and thearubigins. All of the teas contain catechins and tannins in varying amounts.
Other significant constituents include caffeine, theobromine, and theophylline. The polyphenols of green tea are strong antioxidants that help protect against development of vascular plaque, lower cholesterol, and inhibit growth of diarrhea-causing bacteria. Green tea constituents act on the immune system to potentially help block the formation of cancer-causing compounds and suppress cancer-causing agents.
Tea is the second most popular beverage in the world and is consumed for its flavor and stimulant effect.
Current evidence suggests that the polyphenols contained in tea, particularly green tea, may help reduce the risk of certain types of cancers including oral, esophageal, and stomach cancers in humans. Protection against colon, lung, and skin cancer has been shown in animals. The polyphenols include the following catechins: (Catechins are also well recognized as antioxidants and, as such, may decrease the risk of developing atherosclerosis by preventing the oxidation of low density lipoproteins [LDL].)
Epicatechin gallate (ECG)
Epigallocatechin gallate (EGCG)
Of these, epigallocatechin gallate is the largest fraction (40 percent of the polyphenol) and is believed to be the most active. The preventive activities of EGCG are described as anticarcinogenic (preventing cancer promotion), anti-mutagenic (not causing genetic mutations), and anti-reactive (blocking interaction of tumor promoters with their receptors).
The theophylline (and to a lesser extent, theobromine) in tea act as a bronchodilator. Tea has classically been used to treat mild asthma and bronchitis. Although other potent anti-asthma medications are available with more therapeutic benefit, tea may be beneficial for mild respiratory problems and is safe, even for children.
Tea is used as a stimulant drink. The methylxanthines, specifically caffeine, increase alertness and produce mild stimulation.
Green tea has an anti-microbial effect against the bacteria that cause diarrhea, and therefore may help in treating simple diarrhea. Green tea also inhibits oral bacteria. Along with fluoride, tea may help prevent tooth decay.
Please note that this section reports on claims that have NOT yet been substantiated through scientific studies.
Green tea is claimed to be an astringent (useful in stopping hemorrhages), mild diuretic, and effective in lowering cholesterol.
Dosage is measured according to the volume of polyphenols. A common daily dose of green tea is 250 to 350 milligrams of polyphenols twice a day. One cup of brewed tea contains approximately 80 to 100 milligrams of polyphenols.
Different extract strengths are available in capsules. If the product is standardized at 95 percent polyphenols, each capsule will contain about 260 to 360mg of tea extract and should be taken twice a day. If the product is standardized at 50 percent polyphenols, two capsules weighing 375 mg to 525 mg each of tea extract should be taken twice a day. (The powdered extract in capsules is sometimes standardized for epigallocatechin gallate content, and sometimes for total polyphenol content.)
Green tea infused from loose, dried leaves or from tea bags should be steeped in hot, but not scalding, water for a short period of time to preserve the important chemical substances present in the leaf.
As with any caffeine-containing product, green tea can cause anxiety, tremors, irritability, and sleeping problems if taken in excessive doses or by individuals sensitive to caffeine. Side effects are less common with green tea than with other caffeine-containing beverages because the leaves are steeped for a relatively shorter time.
Although the fluoride content of green tea may help prevent tooth decay, tea also contains tannic acid, which can stain teeth.
Tea is used worldwide with no harmful effects, however, as a general rule women who are pregnant or breast-feeding should consult a physician before taking any herbal medicines.
There are no known significant food or drug interactions. However, since green tea acts as a mild stimulant, it is best to avoid using it with other stimulants.
Generally recognized as safe (GRAS). The American Pharmaceutical Association gives Camellia sinensis a rating of 3. A 3 rating indicates that studies on the effectiveness and safety of this substance are conflicting, or there are not enough studies to draw a conclusion.
Approved as an over-the-counter drug.
Japanese Pharmacopoeia (a compendium of drugs recognized by the government).
General sales list (GSL).
Click here for a list of reputable Web sites with general information on nutrition.
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