Green Tea

Common name: Epigallocatechin Gallate (EGCG)

Botanical name: Camellia sinensis

Parts used and where grown

All teas (green, black, and oolong) are derived from the same plant, Camellia sinensis. The difference is in how the plucked leaves are prepared. Green tea, unlike black and oolong tea, is not fermented, so the active constituents remain unaltered in the herb. The leaves of the tea plant are used both as a social and a medicinal beverage.

Green tea has been used in connection with the following conditions (refer to the individual health concern for complete information):

Science Ratings

Health Concerns

Atherosclerosis

Cervical dysplasia (poly E or (-)-epigallocatechin-3-gallate)

Colon cancer (reduces risk)

Breast cancer (risk reduction)

Crohn’s disease

Haemochromatosis (iron overload)

Lung cancer (risk reduction)

Reliable and relatively consistent scientific data showing a substantial health benefit.
2Stars

Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.
1Star

For a herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support and/or minimal health benefit.

Historical or traditional use (may or may not be supported by scientific studies)

According to Chinese legend, tea was discovered accidentally by an emperor 4,000 years ago. Since then, Traditional Chinese Medicine has recommended green tea for headaches, body aches and pains, digestion, depression, immune enhancement, detoxification, as an energizer, and to prolong life.

Active constituents

Green tea contains volatile oils, vitamins, minerals, and caffeine, but the primary constituents of interest are the polyphenols, particularly the catechin called epigallocatechin gallate (EGCG). The polyphenols are believed to be responsible for most of green tea’s roles in promoting good health.¹

Green tea has been shown to mildly lower total cholesterol levels and improve the cholesterol profile (decreasing LDL “bad” cholesterol and increasing HDL “good” cholesterol) in most,² ³ ⁴ ⁵ but not all,⁶ studies. Green tea may also promote cardiovascular health by making platelets in the blood less sticky.

Green tea has also been shown to protect against damage to LDL (“bad”) cholesterol caused by oxygen.⁷ Consumption of green tea increases antioxidant activity in the blood.⁸ Oxidative damage to LDL can promote atherosclerosis. While population studies have suggested that consumption of green tea is associated with protection against atherosclerosis,⁹ the evidence is still preliminary.

Several animal and test tube studies have demonstrated an anticancer effect of polyphenols from green tea.¹⁰ ¹¹ ¹² In one of these studies, a polyphenol called catechin from green tea effectively inhibited metastasis (uncontrolled spread) of melanoma (skin cancer) cells.¹³ The polyphenols in green tea have also been associated with reduced risk of several types of cancer in humans.¹⁴ ¹⁵ ¹⁶ However, some human studies have found no association between green tea consumption and decreased cancer risk.¹⁷ ¹⁸

In a double-blind trial, people with leukoplakia (a pre-cancerous oral condition) took 3 grams orally per day of a mixture of whole green tea, green tea polyphenols, and green tea pigments orally, and also painted a mixture of the tea on their lesions three times daily for six months.¹⁹ As compared to the placebo group, those in the green tea group had significant decreases in the pre-cancerous condition.

Compounds in green tea, as well as black tea, may reduce the risk of dental caries.²⁰ Human volunteers rinsing with an alcohol extract of oolong tea leaves before bed each night for four days had significantly less plaque formation, but similar amounts of plaque-causing bacteria, compared to those with no treatment.²¹

Green tea polyphenols have been shown to stimulate the production of several immune system cells, and have topical antibacterial properties—even against the bacteria that cause dental plaque.²² ²³ ²⁴

One study found that intake of 10 cups or more of green tea per day improved blood test results, indicating protection against liver damage.²⁵ Further studies are needed to determine if taking green tea helps those with liver diseases.

Tea flavonoids given by capsule reduced fecal odour and favourably altered the gut bacteria in elderly Japanese with feeding tubes living in nursing homes.²⁶ The study was repeated in bedridden elderly not on feeding tubes, and green tea was again shown to improve their gut bacteria.²⁷ These studies raise the possibility of using green tea in other settings where gut bacteria are disturbed, such as after taking antibiotics. Further studies are needed to clarify the role of green tea in this respect, however.

High-tannin tea has been shown to reduce the need for blood removal from people with iron overload, or haemochromatosis, in an open study.²⁸ The tea had to be taken with meals and without lemon or milk to be effective. Tea is believed to help in haemochromatosis by preventing iron absorption.

How much is usually taken?

Much of the research documenting the health benefits of green tea is based on the amount of green tea typically consumed in Asian countries—about 3 cups (750 ml) per day (providing 240–320 mg of polyphenols).²⁹ However, other research suggests as much as 10 cups (2,500 ml) per day is necessary to obtain noticeable benefits from green tea ingestion.³⁰ ³¹ To brew green tea, 1 teaspoon (5 grams) of green tea leaves are combined with 1 cup (250 ml) of boiling water and steeped for three minutes. Decaffeinated tea is recommended to reduce the side effects associated with caffeine, including anxiety and insomnia. Tablets and capsules containing standardised extracts of polyphenols, particularly EGCG, are available. Some provide up to 97% polyphenol content—which is equivalent to drinking 4 cups (1,000 ml) of tea. Many of these standardised products are decaffeinated.

Are there any side effects or interactions?

Green tea is generally free of side effects. The most common adverse effects reported from consuming large amounts (several cups per day) of green tea are insomnia, anxiety, and other symptoms caused by the caffeine content in the herb.

An extract of green tea taken by healthy women with a meal inhibited the absorption of non-haem iron (e.g., the form of iron in plant foods) by 26%.³² Frequent use of green tea could, in theory, promote the development of iron deficiency in susceptible individuals.

There are several case reports of people developing liver damage while consuming weight-loss products that contained concentrated extracts of green tea.³³ A cause–effect relationship was not proven, and most of the products contained other ingredients in addition to green tea extract. Nevertheless, researchers have cautioned against the use of large amounts, or concentrated extracts, of green tea.

Are there any drug interactions?
Certain medicines may interact with green tea. Refer to drug interactions for a list of those medicines.

References
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1. Graham HN. Green tea composition, consumption, and polyphenol chemistry. Prev Med 1992;21:334–50.

2. Kono S, Shinchi K, Ikeda N, et al. Green tea consumption and serum lipid profiles: A cross-sectional study in Northern Kyushu, Japan. Prev Med 1992;21:526–31.

3. Yamaguchi Y, Hayashi M, Yamazoe H, et al. Preventive effects of green tea extract on lipid abnormalities in serum, liver and aorta of mice fed an atherogenic diet. Nip Yak Zas 1991;97:329–37.

4. Sagesaka-Mitane Y, Milwa M, Okada S. Platelet aggregation inhibitors in hot water extract of green tea. Chem Pharm Bull 1990;38:790–3.

5. Stensvold I, Tverdal A, Solvoll K, et al. Tea consumption. Relationship to cholesterol, blood pressure, and coronary and total mortality. Prev Med 1992;21:546–53.

6. Tsubono Y, Tsugane S. Green tea intake in relation to serum lipid levels in middle-aged Japanese men and women. Ann Epidemiol 1997;7:280–4.

7. Serafini M, Ghiselli A, Ferro-Luzzi A. In vivo antioxidant effect of green tea in man. Eur J Clin Nutr 1996;50:28–32.

8. Benzie IF, Szeto YT, Strain JJ, Tomlinson B. Consumption of green tea causes rapid increase in plasma antioxidant power in humans. Nutr Cancer 1999;34:83–7.

9. Sasazuki S, Komdama H, Yoshimasu K, et al. Relation between green tea consumption and severity of coronary atherosclerosis among Japanese men and women. Ann Epidemiol 2000;10:401–8.

10. Suganuma M, Okabe S, Sueoka N, et al. Green tea and cancer chemoprevention. Mutat Res 1999;428:339–44.

11. Weisberger JH, Rivenson A, Garr K, et al. Tea, or tea and milk, inhibit mammary gland and colon carcinogenesis in rats. Cancer Lett 1997;114:323–7.

12. Yang CS, Lee MJ, Chen L, Yang GY. Polyphenols as inhibitors of carcinogenesis. Environ Health Perspect 1997;105(Suppl 4):971–6 [review].

13. Menon LG, Kuttan R, Kuttan G. Anti-metastatic activity of curcumin and catechin. Cancer Lett 1999;141:159–65.

14. Mukhtar H, Ahmad N. Green tea in chemoprevention of cancer. Toxicol Sci 1999;52(2 Suppl):111–7.

15. Katiyar SK, Mukhtar H. Tea consumption and cancer. World Rev Nutr Diet 1996;79:154–84 [review].

16. Kohlmeier L, Weterings KG, Steck S, Kok FJ. Tea and cancer prevention: an evaluation of the epidemiologic literature. Nutr Cancer 1997;27:1–13 [review].

17. Tsubono Y, Nishino Y, Komatsu S, et al. Green tea and the risk of gastric cancer in Japan. New Engl J Med 2001;344:632–6.

18. Galanis DJ, Kolonel LN, Lee J, Nomura A. Intakes of selected foods and beverages and the incidence of gastric cancer among the Japanese residents of Hawaii: a prospective study. Int J Epidemiol 1998;27:173–80.

19. 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;220:218–24.

20. Otake S, Makimura M, Kuroki T, et al. Anticaries effects of polyphenolic compounds from Japanese green tea. Caries Res 1991;25:438–43.

21. Ooshima T, Minami T, Aono W, et al. Reduction of dental plaque deposition in humans by oolong tea extract. Caries Res 1994;28:146–9.

22. Stoner GD, Mukhtar H. Polyphenols as cancer chemopreventive agents. J Cell Bioch 1995;22:169–80.

23. You SQ. Study on feasibility of Chinese green tea polyphenols (CTP) for preventing dental caries. Chin J Stom 1993;28:197–9.

24. Hamilton-Miller JM. Antimicrobial properties of tea (Camellia sinensis L.). Antimicro Agents Chemother 1995;39:2375–7.

25. Imai K, Nakachi K. Cross sectional study of effects of drinking green tea on cardiovascular and liver diseases. BMJ 1995;310:693–6.

26. Goto K, Kanaya S, Nishikawa T, et al. The influence of tea catechins on fecal flora of elderly residents in long-term care facilities. Ann Long-Term Care 1998;6:43–8.

27. Goto K, Kanaya S, Ishigami T, Hara Y. The effects of tea catechins on fecal conditions of elderly residents in a long-term care facility. J Nutr Sci Vitaminol 1999;45:135–41.

28. Kaltwasser JP, Werner E, Schalk K, et al. Clinical trial on the effect of regular tea drinking on iron accumulation in genetic haemochromatosis. Gut 1998;43:699–704.

29. Murray MT. The Healing Power of Herbs. Rocklin, CA: Prima Publishing, 1995, 192–6.

30. Imai K, Suga K, Nakachi K. Cancer-preventive effects of drinking green tea among a Japanese population. Prev Med 1997;26:769–75.

31. Imai K, Nakachi K. Cross sectional study of effects of drinking green tea on cardiovascular and liver diseases. BMJ 1995;310:693–6.

32. Samman S, Sandstrom B, Toft MB, et al. Green tea or rosemary extract added to foods reduces nonheme-iron absorption. Am J Clin Nutr 2001;73:607–12.

33. Bonkovsky HL. Hepatotoxicity associated with supplements containing Chinese green tea (Camellia sinensis). Ann Intern Med 2006;144:68–71.

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The information presented in Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or chemist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires March 2007.