Green tea
From Wikipedia, the free encyclopedia
Green tea leaves
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 that regular green tea drinkers have lower chances of heart disease and developing certain types of cancer.Although green tea does not raise the metabolic rate enough to produce immediate weight loss, a green tea extract containing polyphenols and caffeine has been shown to induce thermogenesis and stimulate fat oxidation, boosting the metabolic rate 4% without increasing the heart rate.
According to a survey released by United States Department of Agriculture in 2007,the mean content of flavonoids in a cup of green tea is higher than that in the same volume of other food and drink items that are traditionally considered of health contributing nature, including fresh fruits, vegetable juices or wine. Flavonoids are a group of phytochemicals in most plant products that are responsible for such health effects as anti-oxidative and anticarcinogenic functions. However, as a tea information site points out, the content varies dramatically amongst different tea products,basing on the same USDA survey.
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Chinese tea
Hunan Province- Junshan Yinzhen (Silver Needle tea)[君山银针], known as one of the ten most famous Chinese Teas, is one variety of Yellow Tea, like the Huo Mountain Yellow Buds (霍山黄芽) and the Mengding Yellow Buds (蒙顶黄芽). It is cultivated on Junshan Island, Yueyang City, Hunan Province (湖南省,岳阳,洞庭湖君山).
- 龙井 Longjing
- The most well-known of famous Chinese teas from Hangzhou (杭州), whose name in Chinese means dragon well. It is pan-fried 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.
- 景宁惠明茶 Hui Ming
- Named after a temple in Zhejiang.
- 开化龙顶 Long Ding
- A tea from Kaihua County known as Dragon Mountain.
- 华顶云雾 Hua Ding
- A tea from Tiantai County and named after a peak in the Tiantai mountain range.
- 天目青顶 Qing Ding
- A tea from Tian Mu, also known as Green Top.
- 平水珠茶 Gunpowder
- A popular tea also known as zhuchá. It originated in Zhejiang but is now grown elsewhere in China.
- 洞庭碧螺春 Bi Luo Chun
- 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.
- 南京雨花茶 Rain Flower
- A tea from Nanjing.
- 金坛雀舌 Que She (Tongue of golden altar sparrow)
- originate in Jin Tan city of Jiangsu Province.
- 太湖白云 White Cloud
- Fujian Province is known for mountain-grown organic green tea as well as white tea and oolong tea. The coastal mountains provide a perfect growing environment for tea growing. Green tea is picked in spring and summer seasons.
- Famous tea varieties from this south-eastern region of mainland China include Mao Feng ("fur tip"), Cui Jian ("jade sword") and Mo Li Hua Cha ("dragon pearl") green teas as well as Bai Mu Dan (white peony) white tea and Ti Kwan Yin ("iron goddess") oolong tea. Green tea is heat-cured using ovens or dings; white tea is fast-dried; oolong tea is oxidized through carefully-controlled fermentation.
- Yu Lu
- A steamed tea known as Gyokuro (Jade Dew) made in the Japanese style.
- 信阳毛尖 Xin Yang Mao Jian
- A Chinese famous tea also known as Green Tip, or Tippy Green.
- 珍眉 Chun Mee
- Name means "precious eyebrows"; from Jiangxi, it is now grown elsewhere.
- Gou Gu Nao
- A well-known tea within China and recipient of numerous national awards.
- Yun Wu
- A tea also known as Cloud and Mist.
- 大方 Da Fang
- A tea from Huangshan also known as Big Square suneet.
- 黄山毛峰 Huangshan Maofeng
- A Chinese famous tea from Huangshan.
- 六安瓜片 Lu'An Guapian
- A Chinese famous tea also known as Melon Seed.
- 猴魁 Hou Kui
- A Chinese famous tea also known as Monkey tea.
- 屯绿 Tun Lu
- A tea from Tunxi District.
- 火青 Huo Qing
- A tea from Jing County, also known as Fire Green.
- 雾里青 Wuliqing
- Wuliqing was known since the Song dynasty. Since 2002 Wuliqing is produced again according to the original processing methods by a company called Tianfang (天方). Zhan Luojiu a tea expert and professor at the Anhui Agricultural University who relived its production procedure.
- Hyson
- A medium-quality tea from many provinces, an early-harvested tea.
- 竹叶青茶 Zhu Ye Qing
- Also known as Meng Ding Cui Zhu or Green Bamboo.
- 蒙顶甘露 Meng Ding Gan Lu
- A yellowish-green tea with sweet aftertaste.
Japanese green teas
Green tea (緑茶 Ryokucha) is ubiquitous in Japan and therefore is more commonly known simply as "tea" (お茶 ocha). It is even referred to as "Japanese tea" (日本茶 nihoncha) though it was first used in China during the Song Dynasty, and brought to Japan by Myōan 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 (八女 yame) region of Fukuoka Prefecture and the Uji region of Kyoto. Shizuoka Prefecture produces 40% of raw tea leaf.
- Gyokuro (玉露, Jade Dew)
- Gyokuro is a fine and expensive type that differs from Sencha (煎茶) in that it is grown under the shade rather than the full sun for approximately 20 days.The name "Gyokuro" translates as "jade dew" and refers to the pale green color of the infusion. The shading causes the amino acids (Theanine) and caffeine in the tea leaves to increase, while catechin (the source of bitterness in tea, along with caffeine) decreases, giving rise to a sweet taste. The tea also has a distinct aroma.
- Kabusecha (冠茶, covered tea)
- Kabusecha is made from the leaves grown in the shade prior to harvest, although not for as long as Gyokuro. It has a more delicate flavor than Sencha. It is sometimes marketed as Gyokuro.
- Sencha (煎茶, decocted tea)
- The first and second flush of green tea made from leaves that are exposed directly to sunlight. This is the most common green tea in Japan. The name describes the method for preparing the beverage.
- Fukamushicha (深蒸し茶, long-steamed green tea)
- Sencha which, in the processing of the leaves, has been steamed two times longer than usual Sencha, giving it a deeper color and producing a fuller flavor in the beverage.
- Tamaryokucha (玉緑茶, lit. ball green tea)
- Tamaryokucha has a tangy, berry-like taste, with a long almondy aftertaste and a deep aroma with tones of citrus, grass, and berries. It is also called Guricha.
- Bancha (番茶, coarse tea)
- Lower grade of 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.
- Kamairicha (窯煎茶, 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.
- By-product of Sencha or Gyokuro
- Kukicha (茎茶, stalk tea)
- A tea made from stems, stalks, and twigs. Kukicha has a mildly nutty, and slightly creamy sweet flavor.
- Mecha (芽茶, 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.
- Konacha (粉茶, (coarse) powdered tea)
- Konacha is the dust and smallest parts after processing Gyokuro or Sencha. It is cheaper than Sencha and usually served at Sushi restaurants. It is also marketed as Gyokuroko (玉露粉) or Gyokurokocha.
- Other
- Matcha (抹茶, powdered tea)
- A fine ground tea made from Tencha. 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.
- Genmaicha (玄米茶, 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.
- Hōjicha (焙じ茶, roasted tea)
- A green tea roasted over charcoal (usually Bancha).
- Tencha ( 碾茶, milling tea)
- Half-finished products used for Matcha production. The name indicates its intended eventual milling into matcha. Because, like gyokuro, it is cultivated in shade, it has a sweet aroma. In its processing, it is not rolled during drying, and tencha therefore remains spread out like the original fresh leaf.
- Aracha (荒茶, raw green tea)
- Half-finished products used for Sencha and Gyokuro production. It contains all parts of the tea plant.
- Shincha (新茶, a new tea)
- First flush tea. The name is used for either Sencha or Gyokuro.
- funmatsucha (粉末茶, instant powdered tea)
- Milled green tea, used just like instant coffee. Another name for this recent style of tea is "tokeru ocha," or "tea that melts."
Other green teas
- Green tea from Ceylon
- Kahwah
Production
2006 Green tea production and export. (in thousands of metric tons)
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Steeping
Steeping is the process of making a cup of tea, it is also referred to as brewing. Generally, two grams of tea per 100ml of water, or about one teaspoon of green tea per five-ounce cup (150ml), 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 steeping time and temperature varies with different tea. The hottest steeping temperatures are 180°F to 190°F (81°C to 87°C) water and the longest steeping times two to three 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, regardless of the initial quality. It is thought that excessively hot water results in tannin chemical release, which is especially problematic in green teas as they have higher contents of these. High quality green teas can be and usually are steeped multiple times; two or three steepings is typical. The steeping technique also plays a very important role in avoiding 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. It is common practice for tea leaf to be left in the cup or pot and for hot water to be added as the tea is drunk until the flavor degrades.
Health effects
Green tea contains salubrious polyphenols, particularly catechins, the most abundant of which is epigallocatechin gallate. Green tea also contains carotenoids, tocopherols, ascorbic acid (vitamin C), minerals such as chromium, manganese, selenium or zinc, and certain phytochemical compounds. It is a more potent antioxidant than black tea,although black tea has substances which green tea does not such as theaflavin.
In vitro, animal, preliminary observational, and clinical human studies suggest that green tea can reduce the risk of cardiovascular disease, dental cavities, kidney stones, and cancer, while improving bone density and cognitive function. However, the human studies are inconsistent.Green tea consumption is associated with reduced heart disease in epidemiological studies. Animal studies have found that it can reduce cholesterol. However, several small, brief human trials found that tea consumption did not reduce cholesterol in humans. In 2003 a randomized clinical trial found that a green tea extract with added theaflavin from black tea reduced cholesterol.
A study performed at Birmingham (UK) University, showed 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.
A study performed at the Queen Margaret University, Edinburgh looked at the effects of short term green tea consumption on a group of students between the ages of 19–37.Participants were asked not to alter their diet and to drink 4 cups of green tea per day for 14 days. The results showed that short term consumption of commercial green tea reduces systolic and diastolic Blood Pressure, fasting total cholesterol, body fat and body weight. These results suggest a role for green tea in decreasing established potential cardiovascular risk factors. This study also suggests that reductions may be more pronounced in the overweight population where a significant proportion are obese and have a high risk of cardiovascular disease.
In a study performed at the Israel Institute of Technology, 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.
A study performed at the National institute of Chemistry in Ljubljana, Slovenia, demonstrated that EGCG from green tea inhibits an essential bacterial enzyme gyrase by binding to the ATP binding site of the B subunit. This activity probably contributes to the antimicrobial activity of green tea extract and may be responsible for the effectiveness of green tea in oral hygiene.
In a recent case-control study of the eating habits of 2,018 women, consumption of mushrooms and green tea was linked to a 90% lower occurrence of breast cancer.
A recent study on rats at the University of Hong Kong, published in the February issue of Journal of Agricultural and Food Chemistry, found that the catechins in green tea were absorbed by the lens, retina and other parts of the eye.The absorbed catechins reduced oxidative stress in the eye for up to 20 hours, suggesting that green tea may be effective in preventing glaucoma and other diseases of the eye.
History
Tea consumption has its legendary origins in China of more than 4,000 years ago.Green tea has been used as both a beverage and a method of traditional medicine in most of Asia, including China, Japan, Taiwan, Vietnam, Korea 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. However, many of these claims have not been validated by scientific evidence. Any claims 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.See also flavonoid and 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).
- 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 ten lbs (4.5 kg) in six weeks drinking green tea instead of coffee.
- Some green tea lovers commonly restrict their intake 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
The article Tea: A Story of Serendipity appeared in the March 1996 issue of the United States Food and Drug Administration Consumer Magazine and looked at the potential benefits of green tea. At that time the FDA had not done any reviews of the potential benefits of green tea and were waiting to do so until health claims were filed. The FDA 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", the FDA 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", the FDA 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 study published in the September 13, 2006 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 conducted by Division of Cardiovascular Medicine, Vanderbilt University Medical Center, Nashville, Tennessee; 240 adults were given either theaflavin-enriched green tea extract in form of 375 mg 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.
A more frequent consumption of green tea was associated with a lower prevalence of depressive symptoms in a Japanese study.Researchers conducted a cross-sectional study in 1,058 community-dwelling elderly Japanese individuals 70 years of age. The prevalence of mild and severe depressive symptoms was 34.1 percent and 20.2 percent, respectively. After adjustment for confounding factors, the odds ratios for mild and severe depressive symptoms when higher green tea consumption was compared with green tea consumption of 1 cup/d were: 2 to 3 cups green tea/d and 4 cups green tea/d. Similar relations were also observed in the case of severe depressive symptoms.
Drug interactions
A 2009 study at the University of Southern California using mouse models showed that several of the polyphenolic ingredients of green tea, such as EGCG, can bind with the anticancer drug bortezomib, significantly reducing its bioavailability and thereby rendering it therapeutically useless. This chemical reaction between EGCG and bortezomib is highly specific and depends on the presence of a boronic acid functional group in the bortezomib molecule. Dr. Schönthal, who headed the study, suggests that consumption of green tea, concentrated green tea extract, and other green tea products (such as EGCG capsules) be strongly contraindicated for patients undergoing bortezomib treatment.Caffeine
Unless specifically decaffeinated, green tea contains caffeine. While coffee and tea are both sources of caffeine, the amounts of caffeine in any single serving of these beverages varies significantly. An average serving of brewed coffee contains 145 mg of caffeine, the same serving size of green tea provides 25 mg (black tea provides 47–60 mg and white tea 15 mg).One of the more confusing aspects of caffeine content is the fact that while coffee contains less caffeine than tea when measured in its dry form, the caffeine content of a prepared cup of coffee is significantly higher than the caffeine content of a prepared cup of tea.Safety
In 2008 the US Pharmacopeia reviewed the safety of green tea extract. It found 216 case reports, 34 on liver damage, of which 27 were categorized as possible and 7 were categorized as probable. Potential for adverse effects is increased when extracts are used, particularly on an empty stomach.
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