Green tea is made from the dried leaves of Camellia sinensis, an evergreen shrub. Green tea, black tea, and oolong tea all come from the same plant. Green tea is made by lightly steaming the freshly cut leaf. Green tea is primarily made and consumed in China, Japan, and countries in North Africa and the Middle East.
Unlike black and oolong tea leaves, green tea leaves do not undergo a fermenting process. As a result, green tea has higher levels of antioxidant compounds. Like wine, curcumin, purple sweet potato leaves, and cocoa, green tea is high in compounds called polyphenols. Many of the potential cancer-preventing effects of green tea are thought to involve a compound called catechin. Tea also contains tannins, trace elements, and vitamins.
Green tea is a source of caffeine; one cup of tea contains approximately 50 milligrams of caffeine, depending on the strength of the tea and the size of the cup. For a complete overview of caffeine, information is available in the Natural Standard caffeine monograph.
Green tea is used as an antioxidant to help prevent chronic disease. It has been studied for genital warts, allergy symptoms, anxiety, arthritis, bone health, cancer, heart conditions, the common cold, exercise performance, liver disease, tooth cavities, diabetes, infections, fertility problems, some viruses, high cholesterol, high blood pressure, high triglyceride levels, liver conditions, menopause, mental performance, sun sensitivity, skin conditions and healing, and weight loss.
Although there is good evidence to support green tea use for genital warts and for lowering cholesterol, more research is needed before firm conclusions may be made.
(Czech, Russian, Slovenian), čaje zelené (Czech), čajnoe derevo (Russian), čajovník čínský (Czech), camellia, Camellia assamica, Camellia sinensis, Camellia sinensis (L.) Kuntze, camellia tea, Camellia thea, Camellia theifera, catechins, çay (Turkish), cha (Chinese, Thai, Japanese, Korean, Sinhalese, Urdu), chá (Portuguese - Brazil), cha no ki (Japanese), chaa (Hindi), chaay (Hindi, Sinhalese), chá-da-Índia (Portuguese), chaha (Kannada), chai (Hindi, Russian), chainoe derevo (Russian), chá-preto (Brazilian), chay (Persian, Urdu), chaya (Tamil), Chinese rea, Chinesischer Thee (German), chiya (Nepali), EGC, EGCG, epicatechin gallate, epicatechins, epigallocatechin, (-)-epigallocatechin, epigallocatechin-3-gallate, gamma-aminobutyric acid, green tea extract, GTE, herbata chińska (Polish), hiina teepõõsas (Estonian), Hydroxycut®, ichibi (Japanese), Japanese tea, kamelia (Polish), lignin, lotus-f3, L-theanine, matcha, matcha green tea, matsu-cha tea, methylated EGCG, methylxanthine, nok cha (Korean), O-methylated catechin, organic acids, phenolic acids, phytochemicals, pianta del tè (Italian), planta del té (Spanish), Poly E, polyphenols, Polyphenon E®, proanthocyanidins, shay (Arabic), sinecatechins, sinecatechins 15% ointment, te (Danish, Kannada, Norwegian, Sinhalese, Swedish), tannins, té (Spanish), tea (Hungarian), tea green, tea pigment, tebusk (Danish), tebuske (Swedish), tee (Finnish, German), teekameelia (Estonian), teepensas (Finnish), Teestrauch (German), teestruik (Dutch), teh (Hebrew, Malay), teyaku (Telugu), thayilai (Tamil), thé (French), Thea bohea, Thea sinensis, Thea viridis, Theaceae (family), theanine, theesoortt (Dutch), tTheestrauch (German), theestruik (Dutch), théier (French), theifers, theobromine, theophylline, Veregen®, vitamins.
Combination product examples: AR25®, Exolise®, FertilityBlend (chasteberry extract, green tea extracts, L-arginine, vitamins and minerals), LGNC-07 (green tea extract and L-theanine), LipoKinetix® (norephedrine, caffeine, yohimbine, diiodothyronine, and sodium usnate), Metabolife 356 (caffeine, plus extracts of green tea, Garcinia cambogia, and yerba mate), Nature's Bounty® Green Tea Extract, PhosphoLEAN™ (85mg of N-oleyl-phosphatidylethanolamine extracted from soya lecithin and 121mg of a dry green tea extract), Puritan's Pride® Green Tea Extract.
Note: This monograph focuses on green tea. Green tea contains caffeine. Thus, there may be theoretical uses, safety issues, adverse effects, interactions, and mechanisms of action associated with caffeine that are not specifically addressed in this monograph. For a more complete overview of green tea, information on caffeine is available in the Natural Standard caffeine monograph.
These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Polyphenon E®, a green tea extract, has been FDA-approved for genital warts caused by the human papilloma virus (HPV). A study reports that Polyphenon E® ointment may have antioxidant, anti-inflammatory, and anticancer effects. Polyphenon E® ointment should be used under the care of a doctor or other health professional. Other research suggests that green tea creams may be useful for genital and anal warts and may be a less expensive alternative to regular treatment.
Research suggests that green tea may lower cholesterol; however, studies in people with high cholesterol are limited. Further study in people with this condition is needed before a firm conclusion can be made.
Research suggests that green tea may improve acne by blocking the bacteria that causes this condition. More study is needed to determine the possible benefits of green tea and green tea extract.
Limited research reports that benifuuki green tea reduced symptoms of hay fever caused by Japanese cedar. More studies are needed before a conclusion can be made.
Green tea contains an amino acid called L-theanine, which has been studied and compared to caffeine or alprazolam (Xanax®), for anxiety. L-theanine was found to have positive effects on anxiety under some conditions. However, more high-quality research is needed in this area.
Green tea has been found to have anti-inflammatory benefits. It has been considered for use in osteoarthritis and rheumatoid arthritis. However, research in humans is lacking. More research is needed.
Evidence is mixed from available research of green tea catechins for exercise performance. Further study in this field is needed.
Several reviews have discussed green tea for cancer prevention. Several large studies have looked for a possible link between green tea consumption and cancer incidence. Most research has focused on cancers of the digestive system (stomach, colon, rectum, pancreas, and esophagus), although the risk of breast and prostate cancer have also been studied. Early human research suggests that green tea lacks effect in treating cancer. Further study is needed before a conclusion can be made.
Polyphenols, compounds found in green tea, have been shown to have antiviral effects. Early research suggests that specific green tea formulas may help prevent cold and flu symptoms. In children, drinking one to five cups daily has been linked to a reduced risk of developing the flu. More studies are needed to confirm these results.
There has been limited human research looking at the use of green tea for cavities. Early study suggests that green tea may help decrease plaque. More information is needed before conclusions can be made.
Early research suggests that a combination product called FertilityBlend may help women become pregnant. However, there is a lack of study on the use of green tea alone for fertility. More information is needed in this area.
Gum disease (infection around the tooth)
Green tea intake may decrease signs of inflammation and infection of the tissues around the tooth. Research suggests that green tea extract as part of a combination therapy may help reduce gum bleeding. More well-designed trials are needed before a conclusion can be made.
Several large studies have looked for a possible link between green tea and measures of heart health. Studies have looked at cholesterol levels, blood pressure, and narrowed arteries, and have found a lack of benefit. More research is needed on the use of green tea for treating or preventing heart conditions.
High blood pressure
Early study suggests that green tea may increase blood pressure in people who have high-normal or mild high blood pressure. Recent research suggests that tea in general lacks effect on blood pressure. Other studies report that drinking green tea may help reduce the likelihood of developing high blood pressure. More clinical trials are needed in this area.
Human T-cell lymphocytic virus (carriers)
Early research suggests that green tea may reduce infection severity in people who carry the HTLV-1 virus, which causes cancer of immune system cells. More high-quality research is needed in this area.
Hypertriglyceridemia (high triglycerides)
Early study suggests that green tea may help reduce post-meal triglyceride levels in people who have high triglycerides. Additional research is needed in this area.
Some case reports suggest that green tea products may cause liver damage and inflammation. However, another review reports that increased green tea consumption may reduce liver disease risk. Further study is needed before firm conclusions can be made.
Early research suggests that taking a green tea-containing formula may help relieve menopause symptoms such as hot flashes and problems with sleep. More studies are needed on the effects of green tea alone.
Different types of tea contain different compounds that may help improve cognition. Caffeine may increase alertness and thought. Early non-human research looked at the effects of caffeine, tea, or coffee use on short- and long-term memory and alertness. In limited human research, benefits were lacking on mental performance, mood, and blood flow in the brain. More research is needed before conclusions may be made.
Green tea polyphenols may benefit bone health and quality of life in women with low bone density. However, evidence for bone mass is lacking. More research is needed before a conclusion can be made.
Studies suggest that catechins, the main compounds in green tea, may help fight infection. Green tea consumption has been linked to a lower risk of death from pneumonia in women. More research is needed before a conclusion can be made.
Limited study has found mixed results to support the use of green tea for skin aging caused by sun exposure. More research is needed in this area.
Tuberculosis (management of oxidative stress)
Green tea catechins may help reduce oxidative stress in people who have tuberculosis. More research is needed before a conclusion can be made.
Upper respiratory tract infection
Green tea was found to be less effective than CYSTUS052®, another plant extract, for symptoms of upper respiratory tract infection (infection of the nose or throat). Further research is needed in this area.
Green tea was included in a review of treatments for wound odor control. However, more well-designed studies related to green tea are needed before conclusions can be made.
Early research suggests that green tea may lack an effect on blood sugar or insulin levels in people with diabetes. In people without diabetes, blood sugar levels were higher two hours after a meal consumed with green tea, compared to a meal consumed with water. However, green tea consumption has been linked to a lower risk of diabetes in some research. More research is needed before a firm conclusion can be made.
There are mixed reports on green tea's effects on weight loss. Some research suggests a lack of effect on weight loss or maintenance of weight. Other research reports a small decrease in weight when caffeine was included with green tea. Further study is needed before firm conclusions can be made.