Green tea is made solely from the leaves of Camellia sinensis that have undergone minimal oxidation during processing. Green tea originates from China[1] and has become associated with many cultures throughout Asia. It has recently become more widespread in the West, where black tea is traditionally consumed. Many varieties of green tea have been created in countries where they are grown. These varieties can differ substantially due to variable growing conditions, horticulture,[2] production 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 may have a lower risk of developing heart disease[3] and certain types of cancer.[4] 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.[5]
According to a survey released by the United States Department of Agriculture in 2007,[6] 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.[6] However, based on the same USDA survey, the content of flavanoids may vary dramatically amongst different tea products.[7]
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Tea consumption has its legendary origins in China of more than 4,000 years ago.[8] 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. A book written in the Tang dynasty in china is considered one of the most important in the history of green tea. The book was written by Lu Yu and is called the "Tea Classic" or "Cha Jing". It was written between 600 and 900 AD and spoke about exactly how and where one should enjoy a fine cup of green tea.[9] 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.
Green tea is processed and grown in a variety of ways, depending on the type of green tea desired. As a result of these methods, maximum amounts of polyphenols and antioxidants are retained, giving maximum green tea benefits. The growing conditions can be broken down into two basic types - those grown in the sun and those grown under the shade. The green tea plants are grown in rows that are pruned to produce shoots in a regular manner, and are generally harvested three times per year. The first flush takes place in late April to early May. The second harvest usually takes place from June through July, and the third picking takes place in late July to early August. Sometimes, there will also be a fourth harvest. It is the first flush in the spring which brings the best quality leaves, with higher prices to match. Processed green teas, known as "aracha" are stored under low humidity refrigeration in 30 or 60 kg paper bags at 0-5°C (32-41°F). This aracha has yet to be refined at this stage, with a final firing taking place before blending, selection, and packaging takes place. The leaves in this state will be re-fired throughout the year as they are needed, giving the green teas a longer shelf life and better flavor. The first flush tea of May will readily store in this fashion until the next year's harvest. After this re-drying process, each crude tea will be sifted and graded according to size. Finally, each lot will be blended according to the blend order by the tasters and packed for sale.[10]
Steeping is the process of making a cup of tea; it is also referred to as brewing. In general, two grams of tea per 100ml of water, or about one teaspoon of green tea per five ounce 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 steeping time and temperature varies with different tea. The hottest steeping temperatures are 81°C to 87°C (180°F to 190°F) water and the longest steeping times two to three minutes. The coolest brewing temperatures are 61°C to 69°C (140°F to 160°F) 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. 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.
Hunan Province
Zhejiang Province 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.
Jiangsu Province
Fujian Province
Hubei Province
Henan Province
Jiangxi Province
Anhui Province
Sichuan Province
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.[12] 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.
Green tea contains salubrious polyphenols, in particular 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,[15] although black tea has substances that 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.[15]
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.[16]
A study performed at the University of Birmingham showed that average fat oxidation rates were 17% higher after ingestion of green tea extract than after ingestion of a placebo.[17] Likewise, 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.[18] 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.[19]
A study [20] 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.[21]
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.[22] 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.
2011 research by the Linus Pauling Institute at Oregon State University found that EGCG in green tea has a powerful ability to increase regulatory T cells in the body and boost the immune system and suppress autoimmune disorders.[23]
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, 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."[24] [25]
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."[26][27]
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. To be specific, 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.[28]
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."[29]
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." [30]
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).[31]
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."[32]
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.[33]
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" [34]
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.[35] 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.[36]
A more frequent consumption of green tea was associated with a lower prevalence of depressive symptoms in a Japanese study.[37] 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.
A 2004 study found that components of green tea (catechins) were effective against the parasite Trypanosoma cruzi, which causes Chagas' disease, a major disease in South and Central America.[38]
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.
The weight loss effect of green tea has not been proven completely, though there are some studies that have come back with some promising results. People who are trying to refrain from caffeine intake should remember that green tea also contains caffeine. There are green tea versions available that are without caffeine, so a consumer might want to check for this on the green tea packaging before assuming that the green tea that they are purchasing has no caffeine.
The article Tea: A Story of Serendipity[44] 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 was waiting to do so until health claims were filed. The FDA has since denied two petitions to make qualified health claims as to the health benefits of green tea.[45]
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, the FDA is denying these claims. However, the 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."[46]
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."[47]
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,[48] and added to the "Prescription Drug Product List" in October 2006.[49] Kunecatechins ointment is indicated for the topical treatment of external genital and perianal warts.[50]
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.[51] 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.[52] Use of green tea in conjunction with anticoagulants may result in reduced effectiveness; there is a correlation between the quantity of tea consumed and the method of production may affect the amount of Vitamin K.
Unless specifically decaffeinated, green tea contains caffeine.[53] While coffee and tea are both sources of caffeine, the amount 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).[54] 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.[55]
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, in particular on an empty stomach.[56][57]
2006 Green tea production and export. (in thousands of metric tons)[58]
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On June 17, 2011, radioactive cesium of 1,038 becquerels per kilogram was detected at Charles de Gaulle airport in France in tea leaves imported from Shizuoka Prefecture, Japan, which was more than twice as much as the restricted amount of 500 becquerels per kilogram designated by the European Union, and the government of France announced that they rejected them, which amounted to 162 kilograms.[59] The governor of Shizuoka Prefecture Heita Kawakatsu stated that people who consume the tea leaves "have absolutely no problem when they drink them because it will be diluted to about ten becquerels per kilogram when they steep them even if the leaves have 1,000 becquerels per kilogram," which was a consequence of own examinations of the prefecture.[60] Minister for Consumer Affairs and Food Safety Renhō stated on June 3, 2011, that "there are cases in which aracha are sold as furikake (condiments sprinkled on rice) and so on and they are eaten as they are, therefore we think that it is important to inspect tea leaves including aracha from the viewpoint of consumers' safety."[61]
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