The following articles about Green Tea studys come from Wikipedia, the free Ecyclopedia.

Green tea is made solely with 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 in Asia from Japan and South Korea 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 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 have lower chances of heart disease[3] and developing 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 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, as a tea information site points out, the content varies dramatically amongst different tea products,[7] basing on the same USDA survey.

Oolong (simplified Chinese: 乌龙; traditional Chinese: 烏龍; pinyin: wūlóng) is a traditional Chinese tea (Camellia sinensis) produced through a unique process including withering under the strong sun and oxidation before curling and twisting.[1] Most oolong productions, especially fine quality ones, involved unique tea plant cultivars that are exclusively used for particular varieties.[2] In terms of degree of fermentation, it can range from 8%[3] to 85%,[4] depending on the variety and production style. The popularity of this tea category is closely tied to tea connoisseurs of south China and Chinese expatriates in Southeast Asia,[5] and the tea preparation process that originated from this area: gongfu tea-making, or the gongfu tea infusion approach.

In Chinese tea culture, semi-oxidised oolong teas are collectively grouped as qīngchá (Chinese: 青茶; literally "blue-green tea").[6] The taste of oolong ranges hugely amongst various sub-varieties.[7] It can be sweet and fruity with honey aromas,[8] or woody and thick with roasted aromas,[9][10] or green and fresh with bouquet aromas,[11] all depending on the horticulture and style of production.[12] Several subvarieties of oolong, including those produced in the Wuyi Mountains of northern Fujian and in the central mountains of Taiwan, are among the most famous Chinese teas.

Different varieties of oolong are processed differently, but the leaves are formed into two distinct styles. Some are rolled into long curly leaves, while the others are 'wrap-curled' into small beads each with a tail. The former style is the more traditional of the two.

The name oolong tea comes into the English language from the Chinese name (Chinese: 烏龍茶), meaning "black dragon tea".

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,[12] 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.[12]

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.[13]

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.[14] 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.[15] 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.[16]

A study [17] 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.[18]

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.[19] 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.

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."^{[33] [34]}

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."^{[35][36][dubious – discuss]}

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.^[37]

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."^[38]

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." ^[39]

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).^[40]

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."^[41]

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.^[42]

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" ^[43]

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.^[44] 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.^[45]

A more frequent consumption of green tea was associated with a lower prevalence of depressive symptoms in a Japanese study.^[46] 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.