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Green Tea

Parts Used & 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.

How It Works

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 been shown to protect against the oxidation of cholesterol to a more toxic molecule (oxidized cholesterol).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 odor and favorably 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 hemochromatosis, 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 hemochromatosis by preventing iron absorption.

In a double-blind trial, men with precancerous changes in the prostate received a green tea extract providing 600 mg of catechins per day or a placebo for one year. After one year, prostate cancer had developed in 3.3% of the men receiving the green tea extract and in 30% of those given the placebo, a statistically significant difference.29 These results suggest that drinking green tea or taking green tea catechins may help prevent prostate cancer in men at high risk of developing the disease.

There are four case reports in which certain types of leukemia or lymphoma (low grade B-cell malignancies) improved after the patients began taking green tea extracts.30

References

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(4):197-9.

24. Hamilton-Miller JM. Antimicrobial properties of tea (Camellia sinensis L.). Antimicrob 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. Bettuzzi S, Brausi M, Rizzi F, et al. 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 Res2006;66:1234-40.

30. Shanafelt TD, Lee YK, Call TG, et al. Clinical effects of oral green tea extracts in four patients with low grade B-cell malignancies. Leuk Res 2006;30:707-12.

31. 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.

32. 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.

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

34. 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.

35. Wu AH, Spicer D, Stanczyk FZ, et al. Effect of 2-month controlled green tea intervention on lipoprotein cholesterol, glucose, and hormone levels in healthy postmenopausal women. Cancer Prev Res 2012;5:393-402.

36. Zheng XX, Xu YL, Li SH, et al. Green tea intake lowers fasting serum total and LDL cholesterol in adults: a meta-analysis of 14 randomized controlled trials. Am J Clin Nutr 2011;94:601-10.

37. 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.

38. 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.

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

40. Graham HN. Green tea composition, consumption, and polyphenol chemistry. Prev Med 1992;21:334-50.

41. Kim J, Hwang JS, Cho YK, et al. Protective effects of (-)-epigallocatechin-3-gallate on UVA- and UVB-induced skin damage. Skin Pharmacol Appl Skin Physiol 2001;14:11-9.

42. Katiyar SK. Skin photoprotection by green tea: antioxidant and immunomodulatory effects. Curr Drug Targets Immune Endocr Metabol Disord 2003;3:234-42 [review].

43. Katiyar SK, Perez A, Mukhtar H. Green tea polyphenol treatment to human skin prevents formation of ultraviolet light B-induced pyrimidine dimers in DNA. Clin Cancer Res 2000;6:3864-9.

44. Elmets CA, Singh D, Tubesing K, et al. Cutaneous photoprotection from ultraviolet injury by green tea polyphenols. J Am Acad Dermatol 2001;44:425-32.

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

46. Hill AM, Coates AM, Buckley JD, et al. Can EGCG reduce abdominal fat in obese subjects? J Am Coll Nutr 2007;26:396S–402S.

47. Liu K, Zhou R, Wang B, et al. Effect of green tea on glucose control and insulin sensitivity: a meta-analysis of 17 randomized controlled trials. Am J Clin Nutr 2013;98:340–48.

48. Bettuzzi S, Brausi M, Rizzi F, et al. 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;66:1234-40.

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

50. You SQ. Study on feasibility of Chinese green tea polyphenols (CTP) for preventing dental caries. Chin J Stom 1993;28(4):197-9.

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

52. Matsuo N, Yamada K, Shoji K, et al. Effect of tea polyphenols on histamine release from rat basophilic leukemia (RBL-2H3) cells: the structure-inhibitory activity relationship. Allergy 1997;52:58-64.

53. Plein K, Burkard G, Hotz J. Treatment of chronic diarrhea in Crohn disease. A pilot study of the clinical effect of tannin albuminate and ethacridine lactate. Fortschr Med 1993;111:114-8 [in German].

54. 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.

55. 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.

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

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

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

59. 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.

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

61. Schonthal AH. Adverse effects of concentrated green tea extracts. Mol Nutr Food Res 2011;55:874-885.

62. Liatsos GD, Moulakakis A, Ketikoglou I, Klonari S. Possible green tea-induced thrombotic thrombocytopenic purpura. Am J Health Syst Pharm 2010;67:531-4.

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The information presented by 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 pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires December 2018.

Copyright © 2018 Healthnotes, Inc. All rights reserved.

The information presented by 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. Self-treatment is not recommended for life-threatening conditions that require medical treatment under a doctor's care. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires December 2018.