Green tea

Plant Description:

Green, black, and oolong tea are all derived from the leaves of the Camellia sinensis plant. Originally cultivated in East Asia, this plant grows as large as a shrub or tree. Today, Camellia sinensis grows throughout Asia and parts of the Middle East and Africa.

People in Asian countries more commonly consume green and oolong tea while black tea is most popular in the United States. Green tea is prepared from unfermented leaves, the leaves of oolong tea are partially fermented, and black tea is fully fermented. The more the leaves are fermented, the lower the polyphenol content (See: "What's It Made Of?") and the higher the caffeine content. Green tea has the highest polyphenol content while black tea has roughly 2 - 3 times the caffeine content of green tea.

What's It Made Of?:

Researchers think the health-giving properties of green tea are mostly due to polyphenols, chemicals with potent antioxidant properties. In fact, the antioxidant effects of polyphenols seem to be greater than vitamin C. The polyphenols in green tea also give it a somewhat bitter flavor.

Polyphenols contained in teas are classified as catechins. Green tea contains six primary catechin compounds: catechin, gallaogatechin, epicatechin, epigallocatechin, epicatechin gallate, and apigallocatechin gallate (also known as EGCG). EGCG is the most studied polyphenol component in green tea and the most active.

Green tea also contains alkaloids including caffeine, theobromine, and theophylline. They provide green tea's stimulant effects. L-theanine, an amino acid compound found in green tea, has been studied for its calming effects on the nervous system.

Available Forms:

Most green tea dietary supplements are sold as dried leaf tea in capsule form. Look for standardized extracts of green tea. There are also liquid extracts made from the leaves and leaf buds. The average cup of green tea contains 50 - 150 mg polyphenols (antioxidants). Decaffeinated green tea products contain concentrated polyphenols. Caffeine-free supplements are available.

How to Take It:

Pediatric

Green tea has not been studied in children, so it is not recommended for pediatric use.

Adult

Depending on the brand, 2 - 3 cups of green tea per day (for a total of 240 - 320 mg polyphenols) or 100 - 750 mg per day of standardized green tea extract is recommended. Caffeine-free products are available and recommended.

Precautions:

The use of herbs is a time-honored approach to strengthening the body and treating disease. However, herbs contain active substances that can trigger side effects and interact with other herbs, supplements, or medications. For these reasons, people should take herbs with care, under the supervision of a practitioner knowledgeable in the field of botanical medicine.

People with heart problems or high blood pressure, kidney problems, liver problems, stomach ulcers, and psychological disorders, particularly anxiety, should not take green tea. Pregnant and breastfeeding women should also avoid green tea.

People with anemia, diabetes, glaucoma, or osteoporosis should ask their health care provider before drinking green tea or taking an extract.

People who drink large amounts of caffeine, including caffeine from green tea, for long periods of time may experience irritability, insomnia, heart palpitations, and dizziness. Caffeine overdose can cause nausea, vomiting, diarrhea, headaches, and loss of appetite. If you are drinking a lot of tea and start to vomit or have abdominal spasms, you may have caffeine poisoning. If your symptoms are severe, lower your caffeine intake and see your health care provider.

Possible Interactions:

If you are being treated with any of the following medications, you should not drink green tea or take green tea extract without first talking to your health care provider:

Adenosine -- Green tea may inhibit the actions of adenosine, a medication given in the hospital for an irregular and usually unstable heart rhythm.

Beta-lactam -- Green tea may increase the effectiveness of beta-lactam antibiotics by making bacteria less resistant to treatment.

Benzodiazepines -- Caffeine, including caffeine from green tea, may reduce the sedative effects of these medications commonly used to treat anxiety, such as diazepam (Valium) and lorazepam (Ativan).

Beta-blockers, Propranolol, and Metoprolol -- Caffeine, including caffeine from green tea, may increase blood pressure in people taking propranolol (Inderal) and metoprolol (Lopressor, Toprol XL). These medications are used to treat high blood pressure and heart disease.

Blood Thinning Medications -- People who take warfarin (Coudamin) should not drink green tea. Since green tea contains vitamin K, it can make this medication ineffective. You should not mix green tea and aspirin because they both prevent blood from clotting. Using the two together may increase your risk of bleeding.

Chemotherapy -- The combination of green tea and chemotherapy medications, specifically doxorubicin and tamoxifen, increased the effectiveness of these medications in laboratory tests. However, the same results have not been found in studies on people. On the other hand, there have been reports of both green and black tea extracts affecting a gene in prostate cancer cells that may make them less sensitive to chemotherapy drugs. For that reason, people should talk to their doctors before drinking black and green tea or taking tea extracts while undergoing chemotherapy.

Clozapine (Clozaril) -- The effects of the clozapine may be reduced if taken within 40 minutes after drinking green tea.

Ephedrine -- When taken with ephedrine, green tea may cause agitation, tremors, insomnia, and weight loss.

Lithium -- Green tea has been shown to reduce blood levels of lithium, a medication used to treat bipolar disorder. That can make lithium less effective.

Monoamine Oxidase Inhibitors (MAOIs) -- Green tea may cause a severe increase in blood pressure, called a "hypertensive crisis," when taken together with these drugs used to treat depression. Examples of MAOIs include:

Isocarboxazid (Marplan)
Moclobemide (Manerix)
Phenelzine (Nardil)
Tranylcypromine (Parnate)
Birth control pills -- Oral contraceptives can prolong the amount of time caffeine stays in the body, which may increase its stimulating effects.

Phenylpropanolamine -- A combination of caffeine, including caffeine from green tea, and phenylpropanolamine, used in many over-the-counter and prescription cough and cold medications and weight loss products, may cause mania and a severe increase in blood pressure. The FDA issued a public health advisory in November 2000 to warn people of the risk of bleeding in the brain from use of this medication and urged all manufacturers of this drug to remove it from the market. Most drugs that contained phenylpropanolamine have been reformulated without it.

Quinolone antibiotics -- Green tea may makes these medications more effective and also increase the risk of side effects. These medications include:

Ciprofloxacin (Cipro)
Enoxacin (Penetrex)
Grepafloxacin (Raxar)
Norfloxacin (Chibroxin, Noroxin)
Sparfloxacin (Zagam)
Trovafloxacin (Trovan)
Other medications -- Green tea, especially caffeinated green tea, may interact with a number for medications, including:

Acetaminophen (Tylenol)
Carbamazepine (Tegretol)
Dipyridamole (Persatine)
Estrogen
Fluvoxamine (Luvox)
Methotrexate
Mexiletine (Mexitil)
Phenobarbital
Theophylline
Verapamil (Bosoptin, Calan, Covera- HS, Verelan, Verelan PM)
To be safe, check with your health care provider before drinking or taking green tea if you also take other medications.

Alternative Names:

Camellia sinensis

Reviewed last on: 10/14/2011
Steven D. Ehrlich, NMD, Solutions Acupuncture, a private practice specializing in complementary and alternative medicine, Phoenix, AZ. Review provided by VeriMed Healthcare Network.
Supporting Research

Belza A, Toubro S, Astrup A. The effect of caffeine, green tea and tyrosine on thermogenesis and energy intake. Eur J Clin Nutr. 2007; [Epub ahead of print].

Bettuzzi S, Brausi M, Rizzi F, Castagnetti G, Peracchia G, Corti A. Chemoprevention of human prostate cancer by oral administration of green tea catechins in volunteers with high-grade prostate intraepithelial neoplasia: a preliminary report from a one-year proof-of-principle study. Cancer Res. 2006;66(2):1234-40.

Borrelli F, Capasso R, Russo A, Ernst E. Systematic review: green tea and gastrointestinal cancer risk. Aliment Pharmacol Ther Mar 1, 2004;19(5):497-510.

Boschmann M, Thielecke F. The effects of epigallocatechin-3-gallate on thermogenesis and fat oxidation in obese men: a pilot study. J Am Coll Nutr. 2007;26(4):389S-395S.

Brown AL, Lane J, Holyoak C, Nicol B, Mayes AE, Dadd T. Health effects of green tea catechins in overweight and obese men: a randomised controlled cross-over trial. Br J Nutr. 2011 Jun 7:1-10. [Epub ahead of print]

Cooper R, Morre DJ, Morre DM. Medicinal benefits of green tea: Part I. Review of noncancer health benefits. J Altern Complement Med. 2005;11(3):521-8.

Diepvens K, Westerterp KR, Westerterp-Plantenga MS. Obesity and thermogenesis related to the consumption of caffeine, ephedrine, capsaicin and green tea. Am J Physiol Regul Integr Comp Physiol. 2007;292(1):R77-85.

Fujita H, Yamagami T. Antihypercholesterolemic effect of Chinese black tea extract in human subjects with borderline hypercholesterolemia. Nutr Res. 2008;28(7):450-6.

Fukino Y, Ikeda A, Maruyama K, Aoki N, Okubo T, Iso H. Randomized controlled trial for an effect of green tea-extract powder supplementation on glucose abnormalities. Eur J Clin Nutr. 2007; [Epub ahead of print].

Gross G, Meyer KG, Pres H, Thielert C, Tawfik H, Mescheder A. A randomized, double-blind, four-arm parallel-group, placebo-controlled Phase II/III study to investigate the clinical efficacy of two galenic formulations of Polyphenon(R) E in the treatment of external genital warts. J Eur Acad DermatolVenereol. 2007;21(10):1404-12.

Heck AM, DeWitt BA, Lukes AL. Potential interactions between alternative therapies and warfarin. [review]. Am J Health Syst Pharm. 2000 Jul 1;57(13):1221-1227.

Hsu CH, Liao YL, Lin SC, Tsai TH, Huang CJ, Chou P. Does supplementation with green tea extract improve insulin resistance in obese type 2 diabetics? A randomized, double-blind, and placebo-controlled clinical trial. Altern Med Rev. 2011 Jun;16(2):157-63.

Inoue M, Tajima K, Mizutani M, et al. Regular consumption of green tea and the risk of breast cancer recurrence: follow-up study from the Hospital-based Epidemiologic Research Program at Aichi Cancer Center (HERPACC), Japan. Cancer Lett. 2001;167(2):175-182.

Jian L, Xie LP, Lee AH, Binns CW. Protective effect of green tea against prostate cancer: a case-control study in southeast China. Int J Cancer Jan 1, 2004;108(1):130-135.

Jin X, Zheng RH, Li YM. Green tea consumption and liver disease: a systematic review. Liver Int. 2008;28(7):990-6.

Katiyar SK, Ahmad N, Mukhtar H. Green tea and skin. Arch Dermatol. 2000;136(8):989-94.

Kato A, Minoshima Y, Yamamoto J, Adachi I, Watson AA, Nash RJ. Protective effects of dietary chamomile tea on diabetic complications. J Agric Food Chem. 2008;56(17):8206-11.

Kimura K, Ozeki M, Juneja LR, Ohira H. L-Theanine reduces psychological and physiological stress responses. Biol Psychol. 2007;74(1):39-45.

Koo SI, Noh SK. Green tea as inhibitor of the intestinal absorption of lipids: potential mechanism for its lipid-lowering effect. J Nutr Biochem. 2007;18(3):179-83.

Kovacs EM, Lejeune MP, Nijs I, Westerterp-Plantenga MS. Effects of green tea on weight maintenance after body-weight loss. Br J Nutr Mar 1, 2004;91(3):431-437.

Kuriyama S, Shimazu T, Ohmori K, Kikuchi N, Nakaya N, Nishino Y, Tsubono Y, Tsuji I. Green tea consumption and mortality due to cardiovascular disease, cancer and all causes in Japan: the Ohsaki study. JAMA. 2006;296(10):1255-65.

Lee W, Min WK, Chun S, Lee YW, Park H, Lee do H, Lee YK, Son JE. Long-term effects of green tea ingestion on atherosclerotic biological markers in smokers. Clin Biochem. Jan 1, 2005;38(1):84-87.

Low Dog T, Riley D, Carter T. Traditional and alternative therapies for breast cancer. Alt Ther. 2001;7(3):36-47.

McKenna DJ, Hughes K, Jones K. Green tea monograph. Alt Ther. 2000;6(3):61-84.

Miura Y, Chiba T, Tomita I, et al. Tea catechins prevent the development of atherosclerosis in apoprotein E-deficient mice. J Nutr. 2001;131(1):27-32.

Nagao T, Hase T, Tokimitsu I. A green tea extract high in catechins reduces body fat and cardiovascular risks in humans. Obesity (Silver Spring). 2007;15(6):1473-83.

Peters U, Poole C, Arab L. Does tea affect cardiovascular disease? A meta-analysis. Am J Epidemiol. 2001;154(6):495-503.

Pianetti S, Guo S, Kavanagh KT, Sonenshein GE. Green tea polyphenol epigallocatechin-3 gallate inhibits Her-2/neu signaling, proliferation, and transformed phenotype of breast cancer cells. Cancer Res. 2002;62(3):652-655.

Rowe CA, Nantz MP, Bukowski JF, Percival SS. Specific formulation of Camellia sinensis prevents cold and flu symptoms and enhances gammadelta T cell function: a randomized, double-blind, placebo-controlled study. J Am Coll Nutr. 2007;26(5):445-52.

Ryu OH, Lee J, Lee KW, et al. Effects of green tea consumption on inflammation, insulin resistance and pulse wave velocity in type 2 diabetes patients. Diabetes Res Clin Pract. 2006;71(3):356-8.

Sano T, Sasako M. Green tea and gastric cancer. N Engl J Med. 2001;344(9):675-676.

Sasazuki S, Kodama H, Yoshimasu K et al. Relation between green tea consumption and the severity of coronary atherosclerosis among Japanese men and women. Ann Epidemiol. 2000;10:401-408.

Setiawan VW, Zhang ZF, Yu GP, et al. Protective effect of green tea on the risks of chronic gastritis and stomach cancer. Int J Cancer. 2001;92(4):600-604.

Shankar S, Ganapathy S, Hingorani SR, Srivastava RK. EGCG inhibits growth, invasion, angiogenesis and metastasis of pancreatic cancer. Front Biosci. 2008;13:440-52.

Steptoe A, Gibson EL, Vuonovirta R, Hamer M, Wardle J, Rycroft JA, Martin JF, Erusalimsky JD. The effects of chronic tea intake on platelet activation and inflammation: a double-blind placebo controlled trial. Atherosclerosis. 2007;193(2):277-82.

Suzuki Y, Tsubono Y, Nakaya N, Suzuki Y, Koizumi Y, Tsuji I. Green tea and the risk of breast cancer: pooled analysis of two prospective studies in Japan. Br J Cancer. Apr 5, 2004;90(7)1361-1363.

Thatte U, Bagadey S, Dahanukar S. Modulation of programmed cell death by medicinal plants. [Review]. Cell Mol Biol. 2000;46(1):199-214.

Thavanesan N. The putative effects of green tea on body fat: an evaluation of the evidence and a review of the potential mechanisms. Br J Nutr. 2011 Aug 3:1-13. [Epub ahead of print]

Tsubono Y, Nishino Y, Komatsu S, et al. Green tea and the risk of gastric cancer in Japan. N Engl J Med. 2001;344(9):632-636.

Vinson JA, Teufel K, Wu N. Green and black teas inhibit atherosclerosis by lipid, antioxidant, and fibrinolytic mechanisms. J Agric Food Chem. 2004;52(11):3661-5.

Wargovich MJ, Woods C, Hollis DM, Zander ME. Herbals, cancer prevention and health. [Review]. J Nutr. 2001;131(11 Suppl):3034S-3036S.

Westerterp-Plantenga MS, Lejeune MP, Kovacs EM. Body weight and weight maintenance in relation to habitual caffeine intake and green tea. Obes Res Jul 2005;13(7):1195-1204.

Wu AH, Butler LM. Green tea and breast cancer. Mol Nutr Food Res. 2011 Jun;55(6):921-30.

Yang G, Shu XO, Li H, Chow WH, Ji BT, Zhang X, Gao YT, Zheng W. Prospective cohort study of green tea consumption and colorectal cancer risk in women. Cancer Epidemiol Biomarkers Prev. 2007;16(6):1219-23.

Yang G, Zheng W, Xiang YB, Gao J, Li HL, Zhang X, Gao YT, Shu XO. Green tea consumption and colorectal cancer risk: a report from the Shanghai Men's Health Study. Carcinogenesis. 2011 Sep 8. [Epub ahead of print]

Yuan JM. Green tea and prevention of esophageal and lung cancers. Mol Nutr Food Res. 2011 Jun;55(6):886-904.

Zhang M, Lee AH, Binns CW, Xie X. Green tea consumption enhances survival of epithelial ovarian cancer. Int J Cancer Nov 10, 2004;112(3):465-469.

Zheng J, Yang B, Huang T, Yu Y, Yang J, Li D. Green tea and black tea consumption and prostate cancer risk: an exploratory meta-analysis of observational studies. Nutr Cancer. 2011;63(5):663-72. Epub 2011 Jun 11.

Zhou B, Yang L, Wang L, Shi Y, Zhu H, Tang N, Wang B. The association of tea consumption with ovarian cancer risk: a meta-analysis. Am J Obstet Gynecol. 2007;197(6):594.e1-6.

Source:
http://www.umm.edu/altmed/articles/green-tea-000255.htm