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Green tea
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Green tea is a type of tea made solely with the leaves of Camellia sinensis, that has undergone minimal oxidation during processing. Green tea originates from China and has become associated with many cultures in Asia from Japan to the Middle East. Recently, it has become more widespread in the West, where black tea is traditionally consumed. Many varieties of green tea have been created in countries where it is grown.
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Green tea is a type of tea made solely with the leaves of Camellia sinensis, that has undergone minimal oxidation during processing. Green tea originates from China and has become associated with many cultures in Asia from Japan to the Middle East. Recently, it has become more widespread in the West, where black tea is traditionally consumed. Many varieties of green tea have been created in countries where it is grown. These varieties can differ substantially due to variable growing conditions, processing and harvesting time.
Over the last few decades green tea has been subjected to many scientific and medical studies to determine the extent of its long-purported health benefits, with some evidence suggesting regular green tea drinkers may have lower chances of heart disease and developing certain types of cancer. Green tea has also been claimed useful for weight loss management.
Chinese tea
Zhejiang Province
Zhejiang is home to the most famous of all teas, Xi Hu Longjing, as well as many other high-quality green teas.
- The most well-known of famous Chinese teas from Hangzhou, whose name in Chinese means
dragon well. It is pan-fired and has a distinctive flat appearance. Falsification of Longjing is very common, and most of the tea on the market is in fact produced in Sichuan Province and hence not authentic Longjing.
- Named after a temple in Zhejiang.
- A tea from Kaihua County known as
Dragon Mountain.
- A tea from Tiantai County and named after a peak in the Tiantai mountain range.
- A tea from Tian Mu, also known as
Green Top.
- A popular tea also known as
zhuchá. It originated in Zhejiang but is now grown elsewhere in China.
Jiangsu Province
- A Chinese famous tea also known as
Green Snail Spring, from Dong Ting. As with Longjing, falsification is common and most of the tea marketed under this name may, in fact, be grown in Sichuan.
- A tea from Nanjing.
-
Hubei Province
- A steamed tea known as
Gyokuro (Jade Dew) made in the Japanese style.
Henan Province
* ???? Xin Yang Mao Jian
- A Chinese famous tea also known as
Green Tip, or Tippy Green.
Jiangxi Province
- Name means "precious eyebrows"; from Jiangxi, it is now grown elsewhere.
- A well-known tea within China and recipient of numerous national awards.
- A tea also known as
Cloud and Mist.
Anhui Province
Anhui Province is home to several varieties of tea, including three Chinese famous teas. These are:
- A tea from Mount Huangshan also known as
Big Square.
- A Chinese famous tea from Mount Huang.
- A Chinese famous tea also known as
Melon Seed.
- A Chinese famous tea also known as
Monkey tea.
- A tea from Tunxi District.
- A tea from Jing County, also known as
Fire Green.
- A medium-quality tea from many provinces, an early-harvested tea.
Japanese green teas
is ubiquitous in Japan and therefore is more commonly known simply as . It is even referred to as though it was first used in China during the Song Dynasty, and brought to Japan by Myoan Eisai, a Japanese Buddhist priest who also introduced the Rinzai school of Zen Buddhism.
Types of tea are commonly graded depending on the quality and the parts of the plant used as well as how they are processed. There are large variations in both price and quality within these broad categories, and there are many specialty green teas that fall outside this spectrum. The best Japanese green tea is said to be that from the Yame region of Fukuoka Prefecture and the Uji region of Kyoto. Shizuoka Prefecture produces 40% of raw tea leaf.
?? Bancha (common tea)
-
Sencha harvested as a third or fourth flush tea between summer and autumn. Aki-Bancha (autumn Bancha) is not made from entire leaves, but from the trimmed unnecessary twigs of the tea plant.
??? Genmaicha (brown-rice tea)
-
Bancha (sometimes Sencha) and roasted genmai (brown rice) blend. It is often mixed with a small amount of Matcha to make the color better.
?? Gyokuro (Jade Dew)
- The highest grade Japanese green tea cultivated in special way. Gyokuro's name refers to the pale green color of the infusion. The leaves are grown in the shade before harvest, which alters their flavor. Gyokuro has a high caffeine content (Generally 0.16% in infusion), but the significant L-Theanine content of Gyokuro slows down and counteracts the caffeine assimilation, and also the amount ingested is very small (Generally 10ml - 60ml).
??? Hojicha (roasted tea)
- A green tea roasted over charcoal.
?? Kabusecha (covered tea)
-
Kabusecha is sencha tea, the leaves of which have grown in the shade prior to harvest, although not for as long as Gyokuro. It has a more delicate flavor than Sencha.
??? Kamairicha tea (pan-fried tea)
-
Kamairicha is a pan fried green tea that does not undergo the usual steam treatments of Japanese tea and does not have the characteristic bitter taste of most Japanese tea.
?? Kukicha (stalk tea)
- A tea made from stalks produced by harvesting one bud and three leaves.
???? Karigane
- A tea made from stalks produced of sencha and gyokuro.
?? Matcha (rubbed tea)
- A fine ground tea (?? Ten-cha). It has a very similar cultivation process as Gyokuro. It is used primarily in the tea ceremony. Matcha is also a popular flavor of ice cream and other sweets in Japan.
?? Mecha tea (buds and tips tea)
-
Mecha is green tea derived from a collection of leaf buds and tips of the early crops. Mecha is harvested in spring and made as rolled leaf teas that are graded somewhere between Gyokuro and Sencha in quality.
?? Mugicha (roasted barley tea)
-
Mugicha is a roasted barley tea. It is generally regarded as a cooling summer beverage in Japan.
?? Sencha (broiled tea)
- The first and second flush of green tea, which is the most common green tea in Japan made from leaves that are exposed directly to sunlight. The first flush is also called
shincha (??: a new tea) and specially long steamed leaves mushicha
??? Tamaryokucha
- A tea that has a tangy, berry-like taste, with a long almondy aftertaste and a deep aroma with tones of citrus, grass, and berries.
Other green teas
Brewing
Generally, 2.25 grams of tea per 5 ounces of water, or about one teaspoon of green tea per cup, should be used. With very high quality teas like gyokuro, more than this amount of leaf is used, and the leaf is steeped multiple times for short durations.
Green tea brewing time and temperature varies with individual teas. The hottest brewing temperatures are 180°F to 190°F (81°C to 87°C) water and the longest steeping times 2 to 3 minutes. The coolest brewing temperatures are 140°F to 160°F (61°C to 69°C) and the shortest times about 30 seconds. In general, lower quality green teas are steeped hotter and longer, while higher quality teas are steeped cooler and shorter. Steeping green tea too hot or too long will result in a bitter, astringent brew for low quality leaves. High quality green teas can be and usually are steeped multiple times; 2 or 3 steepings is typical. The brewing technique also plays a very important role to avoid the tea developing an overcooked taste. Preferably, the container in which the tea is steeped or teapot should also be warmed beforehand so that the tea does not immediately cool down.
Caffeine
Unless specifically decaffeinated, Green Tea contains caffeine. Normal green tea itself may contain more caffeine than coffee, but the length of infusion with hot water and the amount of time you use the green tea leaves can greatly reduce your caffeine intake. Experiments have shown after the first 5 minutes of brewing, Green Tea contains 32 mg caffeine. But if the same leaves are then used for a second and then a third five minute brew, the caffeine drops to 12 mg and then 4 mg.
Green teas contain two caffeine metabolites (caffeine-like substances): theophylline, which is stronger than caffeine, and theobromine, which is slightly weaker than caffeine.
Potential effects of green tea on health
Green tea consumption is reportedly associated with various health-promoting properties. For example, it has been shown to promote fat oxidation in humans at rest and to prevent obesity and improve insulin sensitivity in mice.
In a study performed at Birmingham (UK) University, it was shown that average fat oxidation rates were 17% higher after ingestion of Green Tea Extract than after ingestion of a placebo. Similarly the contribution of fat oxidation to total energy expenditure was also significantly higher by a similar percentage following ingestion of Green Tea Extract. This implies that ingestion of Green Tea Extract can not only increase fat oxidation during moderately intensive exercise but also improve insulin sensitivity and glucose tolerance in healthy young men.
In a study performed at the Technion, it was shown that the main antioxidant polyphenol of green tea extract, EGCG, when fed to mice induced with Parkinson's and Alzheimer's disease, helped to protect brain cells from dying, as well as 'rescuing' already damaged neurons in the brain, a phenomenon called neurorescue or neurorestoration. The findings of the study, led by Dr. Silvia Mandell, were presented at the Fourth International Scientific Symposium on Tea and Human Health in Washington D.C., in 2007. Resulting tests underway in China, under the auspices of the Michael J. Fox Foundation, are being held on early Parkinson's patients.
History
Tea consumption had its origin in China more than 4000 years ago. Green tea has been used as traditional medicine in areas such as China, Japan, India and Thailand to help everything from controlling bleeding and helping heal wounds to regulating body temperature, blood sugar and promoting digestion.
The Kissa Yojoki (Book of Tea), written by Zen priest Eisai in 1191, describes how drinking green tea can have a positive effect on the five vital organs, especially the heart. The book discusses tea's medicinal qualities, which include easing the effects of alcohol, acting as a stimulant, curing blotchiness, quenching thirst, eliminating indigestion, curing beriberi disease, preventing fatigue, and improving urinary and brain function. Part One also explains the shapes of tea plants, tea flowers, and tea leaves, and covers how to grow tea plants and process tea leaves. In Part Two, the book discusses the specific dosage and method required for individual physical ailments.
Unproven claims
Green tea has been credited with providing a wide variety of health benefits, many of which have not been validated by scientific evidence. These claims and any for which academic citations are currently missing are listed here:
- Stopping certain neurodegenerative diseases such as Alzheimer's and Parkinson's.
- The prevention and treatment of cancer.
- Treating multiple sclerosis.
- Preventing the degradation of cell membranes by neutralizing the spread of free radicals which occur during oxidation process.
- Reducing the negative effects of LDL cholesterol (bad cholesterol) by lowering levels of triglycerides and increasing the production of HDL cholesterol (good cholesterol).
- Joy Bauer, a New York City nutritionist, says [the catechins in green tea] increase levels of the metabolism speeding brain chemical norepinephrine (noradrenaline).
- Japanese researchers claim that drinking five cups of green tea a day can burn 70 to 80 extra calories. Dr. Nicholas Perricone, a self-proclaimed anti-aging specialist, appeared on The Oprah Winfrey Show and told Oprah's viewers they can lose 10 lbs (4.5 kg) in 6 weeks drinking green tea instead of coffee.
- Some green tea lovers commonly restrict their intake because of the stimulants it contains — equivalent to about a third the amount of caffeine as is found in coffee. Too much caffeine can cause nausea, insomnia, or frequent urination.
United States Food and Drug Administration (FDA)
The article Tea: A Story of Serendipity appeared in the March 1996 issue of FDA Consumer Magazine and looked at the potential benefits of green tea. At that time they had not done any reviews of the potential benefits of green tea and were waiting to do so until health claims were filed. They have since denied two petitions to make qualified health claims as to the health benefits of green tea.
On June 30, 2005, in response to "Green Tea and Reduced Risk of Cancer Health Claim", they stated:
"FDA concludes that there is no credible evidence to support qualified health claims for green tea consumption and a reduced risk of gastric, lung, colon/rectal, esophageal, pancreatic, ovarian, and combined cancers. Thus, FDA is denying these claims. However, FDA concludes that there is very limited credible evidence for qualified health claims specifically for green tea and breast cancer and for green tea and prostate cancer, provided that the qualified claims are appropriately worded so as to not mislead consumers."
On May 9, 2006, in response to "Green Tea and Reduced Risk of Cardiovascular Disease", they concluded "there is no credible evidence to support qualified health claims for green tea or green tea extract and a reduction of a number of risk factors associated with CVD."
However in October 2006, the FDA approved an ointment based on green tea. New Drug Application (NDA) number N021902, for kunecatechins ointment 15% (proprietary name Veregen) was approved on October 31, 2006, and added to the "Prescription Drug Product List" in October 2006. Kunecatechins ointment is indicated for the topical treatment of external genital and perianal warts.
Scientific studies
According to research reported at the Sixth International Conference on Frontiers in Cancer Prevention, sponsored by the American Association for Cancer Research, a standardized green tea polyphenol preparation (Polyphenon E) limits the growth of colorectal tumors in rats treated with a substance that causes the cancer. "Our findings show that rats fed a diet containing Polyphenon E are less than half as likely to develop colon cancer," Dr. Hang Xiao, from the Ernest Mario School of Pharmacy at Rutgers University, Piscataway, New Jersey, noted in a statement.
A 2006 study published in the September 13 issue of the Journal of the American Medical Association concluded "Green tea consumption is associated with reduced mortality due to all causes and due to cardiovascular disease but not with reduced mortality due to cancer." The study, conducted by the Tohoku University School of Public Policy in Japan, followed 40,530 Japanese adults, ages 40-79, with no history of stroke, coronary heart disease, or cancer at baseline beginning in 1994. The study followed all participants for up to 11 years for death from all causes and for up to 7 years for death from a specific cause. Participants who consumed 5 or more cups of tea per day had a 16 percent lower risk of all-cause mortality and a 26 percent lower risk of cardiovascular disease ("CVD") than participants who consumed less than one cup of tea per day. The study also states, "If green tea does protect humans against CVD or cancer, it is expected that consumption of this beverage would substantially contribute to the prolonging of life expectancy, given that CVD and cancer are the two leading causes of death worldwide."
A study in the February 2006 edition of the American Journal of Clinical Nutrition concluded "A higher consumption of green tea is associated with a lower prevalence of cognitive impairment in humans."
In May 2006, researchers at Yale University School of Medicine weighed in on the issue with a review article that looked at more than 100 studies on the health benefits of green tea. They pointed to what they called an "Asian paradox," which refers to lower rates of heart disease and cancer in Asia despite high rates of cigarette smoking. They theorized that the 1.2 liters of green tea that is consumed by many Asians each day provides high levels of polyphenols and other antioxidants. These compounds may work in several ways to improve cardiovascular health, including preventing blood platelets from sticking together (This anticoagulant effect is the reason doctors warn surgical patients to avoid green tea prior to procedures that rely on a patient's clotting ability) and improving cholesterol levels, said the researchers, whose study appeared in the May issue of the Journal of the American College of Surgeons. Specifically, green tea may prevent the oxidation of LDL cholesterol (the "bad" type), which, in turn, can reduce the buildup of plaque in arteries, the researchers wrote.
A study published in the August 22, 2006 edition of Biological Psychology looked at the modification of the stress response via L-Theanine, a chemical found in green tea. It "suggested that the oral intake of L-Theanine could cause anti-stress effects via the inhibition of cortical neuron excitation."
In a double-blind, randomized, placebo-controlled trial done by Division of Cardiovascular Medicine, Vanderbilt University Medical Center, Nashville, Tennessee, 240 adults were given either theaflavin-enriched green tea extract in form of 375mg capsule daily or a placebo. After 12 weeks, patients in the tea extract group had significantly less low-density lipoprotein cholesterol (LDL-C) and total cholesterol (16.4% and 11.3% lower than baseline, p<0.01) than the placebo group. The author concluded that theaflavin-enriched green tea extract can be used together with other dietary approaches to reduce LDL-C.
A study published in the January, 2005 edition of the American Journal of Clinical Nutrition concluded "Daily consumption of tea containing 690 mg catechins for 12 wk reduced body fat, which suggests that the ingestion of catechins might be useful in the prevention and improvement of lifestyle-related diseases, mainly obesity."
According to a Case Western Reserve University School of Medicine study published in the April 13 2005 issue of the Proceedings of the National Academy of Sciences, antioxidants in green tea may prevent and reduce the severity of rheumatoid arthritis. The study examined the effects of green tea polyphenols on collagen-induced arthritis in mice, which is similar to rheumatoid arthritis in humans. In each of three different study groups, the mice given the green tea polyphenols were significantly less likely to develop arthritis. Of the 18 mice that received the green tea, only eight (44 percent) developed arthritis. Among the 18 mice that did not receive the green tea, all but one (94 percent) developed arthritis. In addition, researchers noted that the eight arthritic mice that received the green tea polyphenols developed less severe forms of arthritis.
A German study found that an extract of green tea and hot water (filtered), applied externally to the skin for 10 minutes, three times a day could help people with skin damaged from radiation therapy (after 16-22 days).
A study published in the December 1999 American Journal of Clinical Nutrition found that "Green tea has thermogenic properties and promotes fat oxidation beyond that explained by its caffeine content per se. The green tea extract may play a role in the control of body composition via sympathetic activation of thermogenesis, fat oxidation, or both."
In lab tests, EGCG, found in green tea, was found to prevent HIV from attacking T-Cells. However, it is not yet known if this has any effect on humans.
A study in the August, 2003 issue of a new potential application of Cellular and Molecular Life Sciences found that "a new potential application of (–)-epigallocatechin-3-gallate [a component of green tea] in prevention or treatment of inflammatory processes is suggested"
However, pharmacological and toxicological evidence does indicate that green tea polyphenols can in fact cause oxidative stress and liver toxicity in vivo at certain concentrations. This would imply that consumers should exercise caution when consuming herbal products produced from concentrated green tea extract. Other evidence presented in the review cautions against the drinking of green tea by pregnant women.
Adverse Drug Interactions
A 2009 study at USC by Encouse B. Golden, et al. showed that a main component of green tea, EGCG, binds with the cancer drug Velcade, rendering it therapeutically useless. The authors advise that patients undergoing treatment for multiple myeloma and mantle cell lymphoma, or who are otherwise taking this medication avoid consumption of green tea or any products containing green tea extract.
See also
Literature
External links
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