EGCG accounts for 10-50% of the total catechin content and appears to be the most powerful of the catechins.  Its antioxidant activity is about 25-100 times more potent than vitamins C and E. One cup of green tea may provide 10-40mg of polyphenols and has antioxidant activity greater than a serving of broccoli, spinach, carrots or strawberries.

Research shows that green tea may be anti-atherogenic by helping manage cholesterol & triglycerides levels already in the normal range; supports healthy blood clotting; enhances immune function; and enhances weight loss.

Theoretically, the high antioxidant activity of green tea makes it beneficial by protecting the body from oxidative damage due to free radicals. Many diseases are associated with free radical damage, suppressed immune function, and accelerated aging.

In the laboratory, green tea is an effective antioxidant. It can protect against experimentally induced DNA damage.  There is also evidence from some studies that green tea provides significant immunoprotective qualities, particularly in the case of cancer patients undergoing radiation or chemotherapy.  White blood cell count appears to be maintained more effectively in cancer patients consuming green tea compared to non-supplemented patients.

There may also be an anti-obesity action of green tea.  In one study, mice receiving green tea in their diets had a significant suppression of food intake, body weight gain and fat tissue accumulation.  Also, levels of cholesterol and triglycerides were lower in mice receiving the green tea diet and leptin levels in serum showed a decrease with green tea treatments – indicating that green tea may have a direct effect reducing body weight.

Green tea is second only to water as the most consumed beverage in the world. It has been used medicinally for centuries in India and China. Green tea is prepared by picking, lightly steaming and allowing the tea leaves to dry whereas black tea is fermented before drying. Fermentation can destroy some of the active components of black tea.

Although numerous laboratory investigations have shown the powerful antioxidant activity of green tea and green tea extracts, prospective clinical studies in humans are few. From the laboratory findings, it is clear that green tea is an effective antioxidant, that is provides clear protection from experimentally induced DNA damage and that it can slow or halt the initiation and progression of cancerous tumor growth. There is also evidence from some studies that green tea provides significant immunoprotective qualities, particularly in the case of cancer patients undergoing radiation or chemotherapy. White blood cell count appears to be maintained more effectively in cancer patients consuming green tea compared to non-supplemented patients

In terms of heart disease protection, the potent antioxidant properties of polyphenols would be expected to reduce free radical damage to cells and prevent the oxidation of LDL cholesterol – both of which would be expected to inhibit the formation of atherosclerotic plaques.

Aside from the clear benefits of green tea as an antioxidant, recent studies have suggested a role catechins in promoting weight loss. In one animal study, the anti-obesity effect of green tea was evaluated by feeding different levels of green tea (1-4% in their diets) to female mice for 4 months. The study found that the mice receiving the green tea in their diets had a significant suppression of food intake, body weight gain and fat tissue accumulation. In addition, levels of cholesterol and triglycerides were lower in mice receiving the green tea diet. Perhaps the most interesting finding from this study was that Leptin levels in serum showed a decrease with green tea treatments – indicating that green tea may have a direct effect on the regulation of body weight (downward).

In some studies, green tea is associated with a mild increase in thermogenesis (increased caloric expenditure) – which is generally attributed to its caffeine content.  At least one study has shown that green tea extract stimulates thermogenesis to an extent that is much greater than can be attributed to its caffeine content per se – meaning that the thermogenic properties of green tea may be due to an interaction between its high content of catechin-polyphenols along with caffeine.  A probable theory for the thermogenic effect of green tea is an increase in levels of norepinephrine – because catechin-polyphenols are known to inhibit catechol-O-methyl-transferase (the enzyme that degrades norepinephrine).

One study examined this theory, and the effect of green tea extract on 24-hour energy expenditure in 10 healthy men – who each consumed 3 treatments of green tea extract (50mg caffeine and 90mg epigallocatechin gallate), caffeine (50 mg), and placebo (at breakfast, lunch, and dinner). The results of the study showed that, relative to placebo, the green tea extract resulted in a significant (4%) increase in 24-hour energy expenditure (approximately 80 calories per day) and a significant increase in the body’s use of fat as an energy source (24-h Respiratory Quotient). In addition, the 24-hour urinary norepinephrine excretion was 40% higher during treatment with the green tea extract than with the placebo. It is interesting to note that treatment with caffeine in amounts equivalent to those found in the green tea extract (50mg) had no effect on energy expenditure of fat oxidation – suggesting that the thermogenic properties of green tea is due to compounds other than its caffeine content alone.

Dosage

Typical dosage recommendations are for 1 to 4 cups of green tea per day or 125-500mg/day in tablet form – preferably of an extract standardized to at least 60% polyphenols and/or EGCG as a marker compound.

Side Effects

Green tea consumption of as much as 20 cups per day has not been associated with any significant side effects, other than frequent urination.  In high doses, teas that contain caffeine may lead to restlessness, insomnia, and tachycardia.  Individuals taking aspirin or other anticoagulant medications (including vitamin E and ginkgo biloba) on a daily basis should be aware of the possible inhibition of platelet aggregation (blood clotting) associated with green tea (in some cases, green tea may prolong bleeding times).  Decaffeinated versions of green tea and green tea extracts are available – but the amounts of phenolic/catechin compounds can vary between extracts. 

References

1. Anderson JW, Diwadkar VA, Bridges SR. Selective effects of different antioxidants on oxidation of lipoproteins from rats. Proc Soc Exp Biol Med. 1998 Sep;218(4):376-81.

2. 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(1):83-7.

3. 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.

4. Dulloo AG, Seydoux J, Girardier L, Chantre P, Vandermander J. Green tea and thermogenesis: interactions between catechin-polyphenols, caffeine and sympathetic activity. Int J Obes Relat Metab Disord. 2000 Feb;24(2):252-8.

5. Graham HN. Green tea composition, consumption, and polyphenol chemistry. Prev Med. 1992 May;21(3):334-50.

6. Gupta S, Ahmad N, Mohan RR, Husain MM, Mukhtar H. Prostate cancer chemoprevention by green tea: in vitro and in vivo inhibition of testosterone-mediated induction of ornithine decarboxylase. Cancer Res. 1999 May 1;59(9):2115-20.

7. Hasegawa R, Chujo T, Sai-Kato K, Umemura T, Tanimura A, Kurokawa Y. Preventive effects of green tea against liver oxidative DNA damage and hepatotoxicity in rats treated with 2-nitropropane. Food Chem Toxicol. 1995 Nov;33(11):961-70.

8. Hirose M, Hoshiya T, Akagi K, Futakuchi M, Ito N. Inhibition of mammary gland carcinogenesis by green tea catechins and other naturally occurring antioxidants in female Sprague-Dawley rats pretreated with 7,12-dimethylbenz[alpha]anthracene. Cancer Lett. 1994 Aug 15;83(1-2):149-56.

9. Kao YH, Hiipakka RA, Liao S. Modulation of endocrine systems and food intake by green tea epigallocatechin gallate. Endocrinology. 2000 Mar;141(3):980-7.

10. Lin JK, Liang YC, Lin-Shiau SY. Cancer chemoprevention by tea polyphenols through mitotic signal transduction blockade. Biochem Pharmacol. 1999 Sep 15;58(6):911-5.

11. Muramatsu K, Fukuyo M, Hara Y. Effect of green tea catechins on plasma cholesterol level in cholesterol-fed rats. J Nutr Sci Vitaminol (Tokyo). 1986 Dec;32(6):613-22.

12. Sato D. Inhibition of urinary bladder tumors induced by N-butyl-N-(4-hydroxybutyl)-nitrosamine in rats by green tea. Int J Urol. 1999 Feb;6(2):93-9.

13. Satoh K, Sakagami H. Ascorbyl radical scavenging activity of polyphenols. Anticancer Res. 1996 Sep-Oct;16(5A):2885-90.

14. Sayama K, Lin S, Zheng G, Oguni I. Effects of green tea on growth, food utilization and lipid metabolism in mice. In Vivo. 2000 Jul-Aug;14(4):481-4.

15. Schubert SY, Lansky EP, Neeman I. Antioxidant and eicosanoid enzyme inhibition properties of pomegranate seed oil and fermented juice flavonoids. J Ethnopharmacol. 1999 Jul;66(1):11-7.

16. Tanaka H, Hirose M, Kawabe M, Sano M, Takesada Y, Hagiwara A, Shirai T. Post-initiation inhibitory effects of green tea catechins on 7,12-dimethylbenz[a]anthracene-induced mammary gland carcinogenesis in female Sprague-Dawley rats. Cancer Lett. 1997 Jun 3;116(1):47-52.

17. Wang ZY, Huang MT, Ho CT, Chang R, Ma W, Ferraro T, Reuhl KR, Yang CS, Conney AH. Inhibitory effect of green tea on the growth of established skin papillomas in mice. Cancer Res. 1992 Dec 1;52(23):6657-65.

18. Weisburger JH, Rivenson A, Aliaga C, Reinhardt J, Kelloff GJ, Boone CW, Steele VE, Balentine DA, Pittman B, Zang E. Effect of tea extracts, polyphenols, and epigallocatechin gallate on azoxymethane-induced colon cancer. Proc Soc Exp Biol Med. 1998 Jan;217(1):104-8.

19. Xu Y, Ho CT, Amin SG, Han C, Chung FL. Inhibition of tobacco-specific nitrosamine-induced lung tumorigenesis in A/J mice by green tea and its major polyphenol as antioxidants. Cancer Res. 1992 Jul 15;52(14):3875-9.

20. Yang TT, Koo MW. Chinese green tea lowers cholesterol level through an increase in fecal lipid excretion. Life Sci. 2000;66(5):411-23.

21. Yang TT, Koo MW. Hypocholesterolemic effects of Chinese tea. Pharmacol Res. 1997 Jun;35(6):505-12.

22. Zhu M, Gong Y, Ge G. Effects of green tea on growth inhibition and immune regulation of Lewis lung cancer in mice. Chung Hua Yu Fang I Hsueh Tsa Chih. 1997 Nov;31(6):325-9.