green tea

What Is It?
Health Benefits

Dosage Information

Guidelines for Use

General Interaction

Possible Side Effects



Evidence Based Rating Scale

What Is It?

Legend has it that in ancient times, a Chinese emperor was drinking some hot water when leaves from a nearby tea shrub (Camellia sinensis) dropped into his cup. He apparently liked the soothing drink that resulted from this chance event. And so began what is today a worldwide love affair with tea. It's now second only to water as the most popular drink in the world.

Interestingly, research studies in recent years have confirmed the presence of various healing substances that provide the therapeutic properties long ascribed to the ubiquitous tea leaf. Of particular importance are potent Antioxidant chemicals called Polyphenols that help guard against many kinds of basic cell damage.

To prepare green tea, the leaves of Camellia sinensis are steamed, rolled, and dried. Black and oolong teas come from the same plant, but the leaves are processed differently (they are fermented) and therefore don't provide the same types of therapeutic effects as green tea does. Products labeled gunpowder tea are also green tea. These pellets, imported from China, are just tightly compressed green tea leaves that will unfold when steeped. (1)

In addition to the tea, a number of different forms of green tea supplements are now available.

Health Benefits

Green tea is well-established as a potent source of healing antioxidants--the same beneficial compounds that are found in fruits and vegetables, and even in red wine. The leaf also boasts the presence of notable healing substances such as tannins, phytoestrogens, fluoride, and catechins, the most abundant of which is a superstar antioxidant called EGCG (epigallocatechin-3-gallate).

Many of the medicinal claims made for green tea haven't been examined outside a laboratory setting, specifically, in clinical trials that assess the plant's health effects in people. On the other hand, the pure research findings are exciting, and there certainly appears to be no harm in integrating this ancient brew (or green tea supplements) into your daily diet.

For example, ongoing research suggests that, thanks to its numerous and varied antioxidant compounds, sipping green tea regularly may provide a number of benefits including helping to prevent various types of cancer, guarding against heart disease by lowering cholesterol levels and reducing blood pressure, staving off tooth decay (the tea contains the cavity fighter, fluoride), helping to heal gum infections, and generally promoting longevity.

Researchers have found that as little as ten ounces of green tea will significantly increase the body's antioxidant capacity for at least two hours. These increases are similar to those reported after drinking ten ounces of red wine, another famed source of antioxidants; however, wine should be limited as a health drink because of its alcoholic content.

Because it contains astringent tannin compounds, green tea in moderation can ease indigestion, diarrhea, and other forms of stomach upset. Swiss researchers even have preliminary evidence that green tea accelerates the burning of Fat calories in people who are overweight. A small but interesting 1999 study reported in the American Journal of Clinical Nutrition reported increased energy expenditure and fat oxidation in men who took a green tea Extract as opposed to a Placebo or caffeine alone. (2)

Specifically, green tea may help to:

Counter aging. Given the latest findings on the potent antioxidants in green tea, it's no wonder that this brew has long been touted for promoting long life. Its high antioxidant concentrations apparently enhance longevity by fighting heart disease and cancer, among other ailments. According to epidemiologic studies, Japanese men and women who drink five to ten cups of green tea daily are more likely to live longer and to remain cancer and heart disease-free. (3)

Treat arthritis. Antioxidants in green tea may prevent and reduce the severity of osteoarthritis. Laboratory studies show the catechins in green tea inhibit collagen breakdown. Drinking green tea may reduce inflammation in osteoarthritis and may protect against developing osteoarthritis. (4) In addition, preliminary animal studies suggest green tea's catechins have anti-rheumatic activity and may potentially benefit rheumatoid arthritis; however, additional human studies are warranted before recommending it specifically for this indication. (5)

Prevent cancer. The antioxidant EGCG sets in motion a process called apoptosis, or programmed cell death. Interestingly, the cell death that ensues only affects cancer cells, not healthy ones. (6) EGCG may well enhance the body's natural antioxidant system as well, encouraging the elimination of damaging oxygen molecules called Free radicals.

Numerous studies indicate green tea is beneficial in preventing various cancers. A 2009 review of studies suggests green tea has the potential to protect against colon, skin, lung, breast, and prostate cancer. (7) A 2010 review of three studies shows green tea is a promising agent to protect against prostate cancer. (6) A 2002 review of studies suggests green tea has great promise for preventing bladder cancer and can be safely recommended as part of a healthy diet and lifestyle for overall cancer prevention. (8) Also there is some evidence that women who drink at least one cup of green tea per day have a slightly lower risk of developing ovarian cancer than women who don't drink green tea. (9) Drinking green tea may also protect against oral cancer and inhibit the growth of the lesions of oral leukoplakia, white patches on the mucous membranes in the mouth that can potentially become malignant. (10)

Studies on the prevention of colorectal and esophageal cancers are conflicting. Laboratory and animal studies for green tea in the prevention of colorectal cancer provide strong evidence for a protective effect. However, a 2006 meta-analysis concluded there is insufficient data at this time to support a potential protective effect from green tea for colorectal cancer in humans. (11) Green tea was found to activate cellular antioxidants and inhibit the formation of procarcinogens in the gastrointestinal tract; however, results for green tea’s ability to prevent esophageal cancer are inconsistent. (12) In fact, one large study done over a four-year period found that drinking green tea at high temperatures increased the risk of developing esophageal cancer. (13) Results regarding green tea's ability to protect against lung cancer are also inconsistent. (14)

Prevent diabetes. In a large Japanese study, 17,513 individuals aged 40-65 years who did not have cardiovascular disease, cancer, or type 2 diabetes completed a questionnaire concerning consumption of coffee, black, green, and oolong teas to examine their relationship to physician-diagnosed diabetes over a five-year period. Coffee, caffeine, and green tea were associated with a reduced risk for diabetes for a green tea consumption of at least six cups per day. (15)

Treat genital warts. A specific brand of green tea extract ointment has been approved by the FDA as a prescription for treating genital and perianal warts. Veregen® (Bradley Pharmaceuticals) completely cleared external warts in 24% to 60% of individuals after 10-16 weeks of treatment. (16) In another study, both topical and oral forms of green tea extract were more effective than placebo in treatment of cervical dysplasia caused by the Human Papilloma (wart) virus. (31)

Prevent gingivitis. In one study, 47 individuals with gingivitis received chew candies containing either green tea extracts or placebo eight times per day for four weeks. Individuals received a dental cleaning at the beginning of the study and were instructed to maintain their normal dental cleaning habits. At the end of four weeks, the placebo group experienced worsening plaque formation and gum inflammation while the green tea group had slight improvements, suggesting that green tea may prevent or improve gingivitis. (17)

Treat high cholesterol. Hyperlipidemia—a condition with excess lipids such as cholesterol in the blood—is considered to be a risk factor for coronary heart disease. In one study, a green tea extract enriched with theaflavin taken daily for twelve weeks in a dose of 375mg seemed to mildly reduce low-density lipoproteins (LDL) or "bad" cholesterol. (18) In another study, individuals were given 250mg per day of green tea extract for eight weeks followed by eight weeks of placebo. LDL and total cholesterol levels were reduced at the end of the first eight weeks, which were maintained at the end of the second eight weeks. These results suggested a beneficial effect of green tea on lipid levels. (19) In addition to its lipid-lowering effects, there is some evidence suggesting that green tea may prevent cardiovascular disease, hypertension, and stroke. Studies in humans are inconsistent; however, a large population study in Japan demonstrated reduced overall mortality in cardiovascular disease that resulted primarily from reduced incidence of stroke. More studies are needed before green tea can be recommended specifically for prevention of these conditions. (20-22, 30)

Improve mental alertness and cognitive function. In a preliminary animal study, rats consuming green tea extract in a dose of 400mg per kilogram of body weight demonstrated improved cognitive function. This may be due to green tea's antioxidant properties and may be promising for mental alertness and cognitive function in humans. (23)

Prevent neurological disorders such as Parkinson's and dementia. Animal studies and human epidemiological studies suggest that consumption of green tea, in particular the polyphenols in green tea, may provide a protective benefit against the development of dementia and Parkinson's disease. (24) Other studies suggest the caffeine in green tea provides a protective effect. (25)

Aid in weight loss. Recent studies suggest the caffeine and catechins in green tea may help burn calories. In one study, men taking a green tea extract containing 90mg of the catechin EGCG three times daily burned 266 more calories per day than those taking placebo. (26) A review of studies of alternative weight-loss products indicated green tea consumers experienced significant weight loss. (27)


  • tablet
  • powder
  • liquid
  • dried Herb/tea
  • capsule
  • topical

Dosage Information

Special tips: --Green tea capsules provide a more potent antioxidant effect than a cup of green tea: Green tea leaf is 8% to12% polyphenols (the key antioxidants) while the capsules contain 50% to 90% polyphenols, depending on the brand.

--To get an adequate amount of polyphenols, you need three to four cups of green tea a day or 100 mg of the extract in capsule form. What you do is largely a matter of personal taste. If you want to make green tea your mealtime beverage (as they do in Japan), then obviously you don't need to take extract capsules. If you drink just one cup a day, you may want to add a capsule.

--Antioxidant researchers say that two 8-ounce cups of green tea contain about as many flavonoids (a type of antioxidant) as a serving of vegetables or fruit.

Guidelines for Use

  • The healing properties of green tea can be derived from all of its forms, but brewing the tea may certainly be the most pleasant way to ingest it. Of course, the taste of green tea may not appeal to everyone. A generous dollop of honey makes it more palatable for some people.

  • Preparing the tea with loose leaves provides no benefit over tea bags, but do try to find bags that haven't been lying around for months.

  • For a caffeine-free product, look for decaffeinated green tea to brew or, better yet, switch to capsules, many of which don't contain any caffeine.

  • It doesn't appear to matter what time of day you drink green tea, although doing so throughout the day may be the most beneficial because it provides a constant supply of antioxidants. And remember, green tea does contain caffeine, so drink the brew earlier in the day if you find that it keeps you awake at night.

  • Take green tea supplements at meals with a tall glass of water to ensure optimal absorption and effectiveness.

General Interaction

  • Catechins in green tea and caffeine are reported to have antiplatelet activity. Use caution if taking anti-coagulant medications or herbs that also have this activity, e.g. aspirin, warfarin.

  • Green tea should not be taken with alcoholic beverages or amphetamines as they may increase the side effects of the caffeine in the tea.

  • Green tea may increase the risk of bleeding when combined with anticoagulant and antiplatelet drugs.

  • Green tea may interfere with the activity of diabetes medication.

  • There are a number of medications that may theoretically interact with green tea. If you are taking any medication, consult your physician before supplementing with green tea.

Possible Side Effects

  • Although allergic reactions can occur, most of the potential side effects of green tea are the result of its caffeine content. Most green tea supplements have very little caffeine, about 5 to 6 mg in two 250 mg pills, whereas one cup of brewed tea has about 40 mg of caffeine. However, this is significantly lower than the 107-151 mg caffeine in one cup of coffee. (28) If you drink excessive amounts of brewed tea, you could experience caffeine-related irritability, sleeplessness, irregular heartbeat, dizziness, vomiting, diarrhea, headache, or loss of appetite.

  • Rare cases of hepatoxicity (liver dysfunction) have been reported primarily in relation to oral forms of green tea extract. (32)


  •  Use green tea supplements (which are very low in caffeine) instead of drinking the tea while breast-feeding; the caffeine in the tea can affect a baby's sleep habits adversely.

  • Avoid excess use in pregnancy (greater than two cups/day) as caffeine crosses the placenta and fetal blood levels are comparable to maternal levels.

  • Never brew or drink green tea with boiling water; the high temperature can destroy valuable therapeutic compounds and sipping such hot tea may harm the throat and esophagus. In general, green teas taste better when brewed at temperatures of 140°F-185°F (60°C-85°C). (29) 


1. Green tea. Altern Med Rev. 2000 Aug;5(4):372-5.
2. Dulloo AG, Duret C, Rohrer D, Girardier L, Mensi N, Fathi M, Chantre P, Vandermander J. Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans. Am J Clin Nutr. 1999 Dec;70(6):1040-5.
3. Nakachi K, Eguchi H, Imai K. Can teatime increase one's lifetime? Ageing Res Rev. 2003 Jan;2(1):1-10.
4. Adcocks C, Collin P, Buttle DJ. Catechins from green tea (Camellia sinensis) inhibit bovine and human cartilage proteoglycan and type II collagen degradation in vitro. J Nutr. 2002 Mar;132(3):341-6.
5. Ahmed S. Green tea polyphenol epigallocatechin 3-gallate in arthritis: progress and promise. Arthritis Res Ther. 2010;12(2):208. Epub 2010 Apr 28.
6. Johnson JJ, Bailey HH, Mukhtar H. Green tea polyphenols for prostate cancer chemoprevention: a translational perspective. Phytomedicine. 2010 Jan;17(1):3-13.
7. Butt MS, Sultan MT. Green tea: nature's defense against malignancies. Crit Rev Food Sci Nutr. 2009 May;49(5):463-73. Review.
8. Kamat AM, Lamm DL. Chemoprevention of bladder cancer. Urol Clin North Am. 2002 Feb;29(1):157-68.
9. Nagle CM, Olsen CM, Bain CJ, Whiteman DC, Green AC, Webb PM. Tea consumption and risk of ovarian cancer. Cancer Causes Control. 2010 Sep;21(9):1485-91. Epub 2010 May 20.
10. Li N, Sun Z, Han C, Chen J. The chemopreventive effects of tea on human oral precancerous mucosa lesions. Proc Soc Exp Biol Med. 1999 Apr;220(4):218-24.
11. Sun CL, Yuan JM, Koh WP, Yu MC. Green tea, black tea and colorectal cancer risk: a meta-analysis of epidemiologic studies. Carcinogenesis. 2006 Jul;27(7):1301-9.
12. Koo MW, Cho CH. Pharmacological effects of green tea on the gastrointestinal system. Eur J Pharmacol. 2004 Oct 1;500(1-3):177-85.
13. Wu M, Liu AM, Kampman E, Zhang ZF, Van't Veer P, Wu DL, Wang PH, Yang J, Qin Y, Mu LN, Kok FJ, Zhao JK. Green tea drinking, high tea temperature and esophageal cancer in high- and low-risk areas of Jiangsu Province, China: a population-based case-control study. Int J Cancer. 2009 Apr 15;124(8):1907-13.
14. Lee AH, Liang W, Hirayama F, Binns CW. Association between green tea consumption and lung cancer risk. J Prev Med Public Health. 2010 Jul;43(4):366-7.
15. so H, Date C, Wakai K, et al; JACC Study Group. The relationship between green tea and total caffeine intake and risk for self-reported type 2 diabetes among Japanese adults. Ann Intern Med 2006;144:554-62.
16. Meltzer SM, Monk BJ, Tewari KS. Green tea catechins for treatment of external genital warts. Am J Obstet Gynecol. 2009 Mar;200(3):233.e1-7.
17. Krahwinkel T, Willershausen B. The effect of sugar-free green tea chew candies on the degree of inflammation of the gingiva. Eur J Med Res 2000;5:463-7.
18. Maron DJ, Lu GP, Cai NS, et al. Cholesterol-lowering effect of a theaflavin-enriched green tea extract: a randomized controlled trial. Arch Intern Med 2003;163:1448-53.
19. Batista Gde A, Cunha CL, Scartezini M, von der Heyde R, Bitencourt MG, Melo SF. Prospective double-blind crossover study of Camellia sinensis (green tea) in dyslipidemias. Arq Bras Cardiol. 2009 Aug;93(2):128-34.
20. Clement Y. Can green tea do that? A literature review of the clinical evidence. Prev Med. 2009 Aug-Sep;49(2-3):83-7. Epub 2009 May 22.
21. Schneider C, Segre T. Green tea: potential health benefits. Am Fam Physician. 2009 Apr 1;79(7):591-4. Review.
22. Stangl V, Lorenz M, Stangl K. The role of tea and tea flavonoids in cardiovascular health. Mol Nutr Food Res. 2006 Feb;50(2):218-28.
23. Xu Y, Zhang JJ, Xiong L, Zhang L, Sun D, Liu H. Green tea polyphenols inhibit cognitive impairment induced by chronic cerebral hypoperfusion via modulating oxidative stress. J Nutr Biochem. 2010 Aug;21(8):741-8.
24. Mandel SA, Amit T, Kalfon L, Reznichenko L, Youdim MB. Targeting multiple neurodegenerative diseases etiologies with multimodal-acting green tea catechins. J Nutr. 2008 Aug;138(8):1578S-1583S.
25. Ross GW, Abbott RD, Petrovitch H, et al. Association of coffee and caffeine intake with the risk of parkinson disease. JAMA 2000;283:2674-9.
26. Dulloo AG, Duret C, Rohrer D, et al. Efficacy of a green tea extract rich in catechin polyphenols and caffeine in increasing 24-h energy expenditure and fat oxidation in humans. Am J Clin Nutrition 1999;70:1040-1045.
27. de Lira-García C, Souto-Gallardo M, Bacardí-Gascón M, Jiménez-Cruz A. [A systematic review of the effectiveness of alternative weight-loss products' ingredients] Rev Salud Publica (Bogota). 2008 Nov-Dec;10(5):818-30.
28. Bunker ML, McWilliams M. Caffeine content of common beverages. J Am Diet Assoc. 1979 Jan;74(1):28-32.
29. The Fragrant Leaf. Accessed 9/20/2010.
30. Kuriyama S, Shimazu T, Ohmori K, et al. Green tea consumption and mortality due to cardiovascular disease, cancer, and all-cause mortality. JAMA 2006;296:1255-65.
31. Ahn WS, Yoo J, Huh SW, et al. Protective effects of green tea extracts (polyphenon E and EGCG) on human cervical lesions. Eur J Cancer Prev 2003;12:383-90.
32. Bonkovsky HL, Hepatotoxicity Associated with Supplements Containing Chinese Green Tea (Camellia sinensis). 2006;144(1):68-71.

Evidence Based Rating Scale

The Evidence Based Rating Scale is a tool that helps consumers translate the findings of medical research studies and what our clinical advisors have found to be efficacious in their personal practice into a visual and easy to interpret format. This tool is meant to simplify the information on supplements and therapies that demonstrate promise in the treatment of certain conditions.



Date Published: 04/18/2005
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