Green tea is tea made solely with the leaves of Camellia sinensis that have 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 that regular green tea drinkers have lower chances of heart disease and developing certain types of cancer. Green tea has also been claimed as useful for "weight loss management" possibly by inducing thermogenesis and stimulating fat oxidation.
Zhejiang is home to the most famous of all teas, Xi Hu Longjing (西湖龙井), as well as many other high-quality green teas.
Hua Ding
A tea from Tiantai County (天台县) and named after a peak in the Tiantai mountain (天台山) range.
Hui Ming ‡
Hui Ming Tea is named after a temple in Zhejiang.
Long Ding (lit. "Dragon Mountain")
A tea from Kaihua County (开化县), known as Dragon Mountain.
Longjing (龙井; lit. "Dragon Well") †
Xi Hu Long Jing(西湖龙井). The most well-known of famous Chinese teas from the West Lake (西湖) district in Hangzhou (杭州), 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 (四川) Province and hence not authentic Longjing.
Qing Ding (Green Top)
A tea from Tian Mu (天目), also known as Green Top. Tian Mu mountain is located in Lin An county (临安市) in the north west of Zhejiang province (浙江省). There are two 1500-meter peaks, each with a pond on top filled with crystal clear water looking like an eye, hence the name of Eyes on Heaven.
Gunpowder (珠茶; pinyin: zhū chá) †
A popular tea also known as zhuchá. It originated in Shaoxing County (simplified Chinese: 绍兴; traditional Chinese: 紹興; pinyin: Shàoxīng; Wade-Giles: Shao-hsing), Zhejiang but is now grown elsewhere in China.
Anhui Province is home to several varieties of tea, including three Chinese famous teas. These are:
Da Fang (Chinese: 大方)
A tea from Mount Huangshan also known as Big Square suneet. It is grown at the south of Huangshan in Xi County (歙縣) of Anhui Province, in China. It has similarities to Longjing and a nutty aroma.
Huang Shan Mao Feng (黄山毛峰; Fur Peak)
A Chinese famous tea from Huangshan (黄山). The tea is grown near Huangshan (Yellow) Mountain, which is home to many famous varieties of Green Tea. Huangshan Mao Feng Tea's English translation is "Yellow Mountain Fur Peak" due to the small white hairs which cover the leaves and the shape of the processed leaves which resemble the peak of a mountain.
Liu An Gua Pian (六安瓜片)
A Chinese famous tea. The tea is a Green tea from Liu An County in China's Anhui Province. The literal translation for Liu An Gua Pian Tea is Liu An Melon Seed Tea. Its name is derived from the shape of the processed tea leaves, which are flat and oval and resemble a melon seed.
Hou Kui (猴魁) ‡
Taiping Hou Kui (simplified Chinese: 太平猴魁; pinyin: tàipíng hóukuí lit. "peaceful monkey leader") tea is a Chinese famous tea also known as Monkey tea. It is grown at the foot of Huangshan (黄山) in Taiping County, Anhui.
Tun Lu (屯绿)
A tea from Tunxi District (屯溪区, pinyin : tún xī qū).
Huo Qing (火青)
A tea from Jing County (simplified Chinese: 泾县; pinyin: Jīng Xiàn), also known as Fire Green.
Wuliqing (雾里青)
Wuliqing was known since the Song dynasty (Chinese: 宋朝; pinyin: Sòng Cháo; Wade-Giles: Sung Ch'ao). 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 (Lucky Dragon)
Hyson or Lucky Dragon Tea is a Chinese green tea that comes from the Anhui Provence of China. It is made from young leaves that are thinly rolled to have a long, twisted appearance that unfurls when brewed. The name Hyson is likely a Chinese name meaning "flourishing spring" or "blooming spring," emerging between 1730-40 in the Chinese dialect Guangdong as "héichēun". While hyson tea is often thought of as low-grade or mediocre quality tea, young hyson is considered high quality.
Bi Luo Chun (Chinese: 碧螺春; pinyin: Bìluóchūn) †
Dong Ting Bi Luo Chun (洞庭碧螺春; Green Snail Spring). 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 (四川).
Rain Flower
A tea from Nanjing (Chinese: 南京; Pinyin: Nánjīng; Wade-Giles: Nan-ching; Postal map spelling: Nanking).
Shui Xi Cui Bo
Chun Mee (珍眉, Eyebrow tea)
Chun Mee (珍眉) is a popular green tea. Its name means "precious eyebrows." It has a dusty appearance and is generally more acidic and less sweet than other green teas. It was originally produced only in the Jiangxi province, but is now grown elsewhere.
Gou Gu Nao
A well-known tea within China and recipient of numerous national awards.
Yun Wu (Cloud and mist)
A tea also known as Cloud and Mist.
The Fujian Province is known for mountain-grown organic green tea as well as white and oolong teas (乌龙茶). 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 (毛峰, lit. "fur tip"), Cui Jian ("jade sword") and Mo Li Hua Cha ("dragon pearl") green teas as well as Bai Mu Dan (Chinese: 白牡丹, Pinyin: bái mǔ dān, Jyutping: baak6 maau5 daan1, POJ: peh bo tan; literally "white peony") white tea and Ti Kwan Yin (simplified Chinese: 铁观音; traditional Chinese: 鐵觀音; pinyin: tiěguānyīn; Min Nan POJ: Thih-koan-im; Cantonese Jyutping: tit3 gwun1 yam1; literally meaning iron guanyin) oolong tea. Green tea is heat-cured using ovens or dings; white tea is fast-dried; oolong tea is oxidized through carefully-controlled fermentation.
Junshan Yinzhen (simplified Chinese: 君山银针; traditional Chinese: 君山銀針; pinyin: jūn shān yín zhēn, lit. "Silver Needle(s) of the Gentleman Mountain")
It is a Yellow tea from Junshan Island of Hunan Province in China. It is one of Chinese famous Teas. Although the same kind of tea trees are also planted around Dongting Lake, where Junshan Island is located, those teas should not be called Junshan Yinzhen.
Yu Lu (玉露; yùlù)
A steamed tea known as Gyokuro (Jade Dew) made in the Japanese style. Gyokuro (玉露) is a fine and expensive type of green tea from Japan.
Guangdong Province has few green teas and most of them are mainly consumed within the province.
West Mountain
This green tea is a traditional tea variety in Guangxi Province.
Mao Jian
Mao jian is one of common variety in Chinese green tea distinguished by its hairy, fine, and corded appearance.
Zhu Ye Qing
Also known as Meng Ding Cui Zhu or Green Bamboo.
Meng Ding Gan Lu (Chinese: 蒙顶甘露)
A yellowish-green tea with sweet aftertaste. It is the most famous tea from Mount Meng Shan, Sichuan Province in the southwest part of China. Ganlu is translated as "Sweet Dew", which refers to sweet flavor and taste of the tea.
White Hair
The Tea is from Menghai County (勐海县; pinyin: Měnghǎi Xiàn).
Xin Yang Mao Jian (信阳毛尖) †‡
Xin Yang Mao Jian tea (信阳毛尖) is a green tea produced in Xinyang, Henan. It is designated as a China Famous Tea. It is also known as Green Tip, or Tippy Green.
17. Tibet (Tibetan: བོད་; Wylie: bod, pronounced [pʰø̀ʔ]; Chinese: 西藏; pinyin: Xī Zàng)
† One of top-ten Chinese teas.
‡ Awarded gold medal in Panama Pacific International Exposition, San Francisco, 1915.
Steeping
While commonly called brewing, the process of making a cup of tea is actually steeping. Generally, 2 grams of tea per 100ml of water, or about one teaspoon of green tea per 5 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 individual teas. The hottest steeping 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, 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; 2 or 3 steepings is typical. The steeping 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. 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 recent study 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 had its origin in China more than 4000 years ago. Green tea has been used as both a beverage and a method of traditional medicine in most of Asia, including China, Japan, Vietnam, Korea, 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 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
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 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 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. Normal green tea itself may contain more caffeine than coffee (by dry weight--for caffeine per serving size), but the length of infusion with hot water and the number of times the leaves are reused can greatly alter caffeine intake. Using a given amount of green tea leaves steeped in 100 mL of water, experiments have shown that after the first 5 minutes of brewing, the 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, respectively.
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 coffee contains the most caffeine, the same serving size of tea provides 1/2 to 1/3 as much. One of the more confusing aspects of caffeine content is the fact that 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.
Green teas contain two caffeine metabolites (caffeine-like substances): theophylline, which is a stronger stimulant than caffeine, and theobromine, which is slightly weaker than caffeine.
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.
References
http://en.wikipedia.org/wiki/Green_tea
http://en.wikipedia.org/wiki/Chinese_tea
http://en.wikipedia.org/wiki/China_Famous_Tea
http://www.green-tea-store.com/map/map.html
Chinese tea | Dietary antioxidants | Green tea | Monoamine oxidase inhibitors
This page was last modified on 16 May 2010 at 08:34.
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