Top Benefits of Green Tea
Consumption of green tea has been documented since 2700 BC, and many epidemiological and interventional studies have shown either a strong correlation or a cause-effect relationship with many beneficial health effects of drinking 3-10 cups of tea per day. In addition, many intervention studies have been performed on various extracts of green tea in an attempt to identify the mechanism of action of the individual components, especially the polyphenols.
EGCg (Epi Gallo-Catechin-3-Gallate) is one of the more extensively studied green tea polyphenols, as it was believed and proven to account for many of the benefits observed from dry green tea or green tea extract consumption.
An average cup of green tea is typically made from 5 g dry green tea leaves which provide about 240-320 mg polyphenols (19) and among these, EGCg constitutes about 200 mg (12).
It peaks in the plasma 2 hours after consumption and levels return to baseline after 24 hrs. By isolating a single compound for interventions, studies have been able to elucidate the mechanisms of action behind specific physiological effects, although for supplementation/consumption purposes, it is still advisable to consume the tea or tea extracts that contain a wide array of naturally occurring substances.
In general, the overall effect of naturally occurring mixtures of substances tend to exhibit a greater effect than the sum of the individual components, often due to synergy. For quality and effectiveness, standardized extracts are advisable, as they guarantee a potent amount of the desirable active component with research proven benefits, as is the case with EGCg.
Benefits of Green Tea
Consumption of green tea was shown to increase antioxidant activity in the blood (19).
Increased Energy Expenditure
Administration of a green tea extract containing 375 mg catechins (270 mg EGCg) and 150 mg of caffeine three times per day, to human sedentary subjects, has increased the 24-hr EE (Energy Expenditure) by 4% which can translate into an average of an extra 100-150 calories burned per day. This was thought to be due to the increase in the post meal thermogenesis component of the EE by approximately 40%. Given that the subjects were sedentary, it is conceivable that the difference could have been more substantial with additional exercise induced thermogenesis. More studies on this are needed. The effect was clearly proven to be due to more than that of the caffeine content alone. The mechanism of action of green tea polyphenols is believed to be the inhibition of the COMT enzyme, which degrades NE (norepinephrine), thus prolonging its lipolytic effect. Tyrosine supplementation may be helpful in supporting the optimal production of norepinephrine, especially during stressful states. (1)
Improved Fat Metabolism
In the same study mentioned above, the percentage of calories derived from fat burned for the 24-hr EE, was 41% in the green tea group versus 31% in the control group, while following the same diet and sedentary activity pattern. This showed a metabolic shift from burning carbohydrates to burning fat, since the percentage of calories derived from carbohydrates was 42% in the green tea group versus 55% in the control. Another animal study showed that green tea polyphenols inhibit pancreatic lipase, thus reducing triglycerides and cholesterol absorption and preventing weight gain. (6)
In animal models, EGCg was shown to cause a reduction in food intake. (5)
Blood Glucose Management
Green tea components were shown to influence various metabolic pathways related to the blood glucose control in animal models:
- EGCg inhibits intestinal glucose uptake performed by sodium dependent glucose transporter (7).
- Green tea supplementation ameliorates insulin resistance and increases glucose transporter IV content in a fructose-fed rat model (8).
- EGCg reduces hepatic glucose production (9).
- EGCg suppresses inflammatory damage on pancreatic beta-cell, characteristic of Type I diabetes (10).
Green tea exerts protective effects on the brain due to its powerful antioxidant activity, for example during ischemic brain reperfusion injury (11). It also seems to be a great candidate for stalling neurodegeneration through additional newly discovered mechanisms (12).
Green tea consumption was shown to protect LDL cholesterol from oxidation, cause a small decrease in LDL levels and reduce platelet aggregation (16). With regards to blood pressure, it should be used with caution: a human study showed no significant ambulatory average increases in BP for regular tea consumers of 5 cups per day (around 2000mg polyphenols), although there was a mild elevation by 5mmHg/1mmHg 60 minutes after consumption.(18)
Reduced Risk of Cancer Development and Metastasis: Through protection against mutagenic substances (such as: smoking, UV light, dietary carcinogens), enhanced detoxification, reduced cell proliferation (by inhibiting IGF-1 pathway and PGE2 formation) and angiogenesis while increasing apoptosis in cancer cells only. In animal models, it was shown to increase the effectiveness of chemotherapy. In animal and human epidemiological studies, the following types of cancers showed reduced incidence and severity in association with green tea consumption: lung, stomach, colon, pancreas, liver, breast, prostate, skin.(13, 14)
Skin Aging & Skin Cancer Protection
Research suggests that GTP (green tea polyphenols) as a dietary supplement could be useful to attenuate solar UVB light-induced premature skin aging. (22)
Reduction of Inflammation
Green tea polyphenols inhibit pathways related to the production of inflammatory mediators COX2 and LOX enzymes and exert anti-histamine action.(16, 21)
Antibacterial and Antiviral Action
EGCg was shown to be effective in conjunction with antibiotic treatment for H. Pylori and against other antibiotic resistant bacteria. (13, 23)
Testosterone is converted by 5-AR (5-alpha reductase) to DHT (Dihydrotestosterone) in various cells in the body, such as epidermal and prostate cells. DHT is thought to contribute to the development of male pattern baldness, acne, hirsutism (excessive facial/body hair in females), as well as prostate enlargement and cancer.
Some popular pharmacological agents used for hair loss inhibit only 5-AR Type 2, expressed in Prostate cells, with no effect on epidermal cells, which express 5-AR type 1. Green tea polyphenols inhibit 5-AR type 1, which makes green tea a good complement to these hair loss formulas and a good candidate for reducing the occurrence and reoccurrence of male pattern baldness, acne and hirsutism. (21)
Green tea polyphenols enhance the glucuronidation detoxification pathways.
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4. Choo JJ. Green tea reduces body fat accretion caused by high-fat diet in rats through beta-adrenoceptor activation of thermogenesis in brown adipose tissue. J Nutr Biochem. 2003 Nov; 14(11): 671-6.
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6. Juhel C, Armand M, Pafumi Y et al. Green tea extract (AR 25) inhibits lipolysis of triglycerides in gastric and duodenum medium in vitro. J Nutr Biochem 2000;11:45-51.
7. Kobayashi Y, Suzuki M . Green tea polyphenols inhibit the sodium-dependent glucose transporter of intestinal epithelial cells by a competitive mechanism. J Agric Food Chem. 2000 Nov; 48(11): 5618-23.
8. Wu LY, Juan CC . Green tea supplementation ameliorates insulin resistance and increases glucose transporter IV content in a fructose-fed rat model. Eur J Nutr. 2004 Apr;43(2):116- 24. Epub 2004 Jan 06.98.
9. Waltner-Law ME, Wang XL Epigallocatechin gallate, a constituent of green tea, represses hepatic glucose production. J Biol Chem. 2002 Sep 20;277(38):34933-40. Epub 2002 Jul 12.
10. Han MK. Epigallocatechin gallate, a constituent of green tea, suppresses cytokine-induced pancreatic beta-cell damage. Exp Mol Med. 2003 Apr 30;35(2):136-9.
11. Hong JT, Ryu SR . Neuroprotective effect of green tea extract in experimental ischemia-reperfusion brain injury. Brain Res Bull. 2000 Dec;53(6):743-9.
12. Kostrzewa RM, Segura-Aguilar J. Novel mechanisms and approaches in the study of neurodegeneration and neuroprotection. a review. Neurotox Res. 2003;5(6):375-83.
13. Mukhtar H, Ahmad N. Tea polyphenols: prevention of cancer and optimizing health. Am J Clin Nutr. 2000 Jun;71(6 Suppl):1698S-702S; discussion 1703S-4S.
14. Demeule M, Michaud-Levesque J . Green tea catechins as novel antitumor and antiangiogenic compounds. Curr Med Chem Anti-Canc Agents. 2002 Jul;2(4):441-63.
15. Rutter K, Sell DR . Green tea extract suppresses the age-related increase in collagen crosslinking and fluorescent products in C57BL/6 mice. Int J Vitam Nutr Res. 2003 Nov;73(6):453-60.
16. Sueoka N, Suganuma M . A new function of green tea: prevention of lifestyle-related diseases. Ann N Y Acad Sci. 2001 Apr;928:274-80.
17. Liao S.The medicinal action of androgens and green tea epigallocatechin gallate. Hong Kong Med J. 2001 Dec;7(4):369-74
18. Hodgson JM, Puddey IB. Effects on blood pressure of drinking green and black tea. J Hypertens. 1999 Apr;17(4):457-63.
19. 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.
20. Murray MT. The Healing Power of Herbs. Rocklin, CA: Prima Publishing, 1995, 192-6.
21. Alexis AF, Jones A., Potential therapeutic applications of tea in dermatology. Int J Dermat 1999, 38, 735-743.
22. Vayalil PK, Mittal A, Hara Y, Elmets CA, Katiyar SK. Green tea polyphenols prevent ultraviolet light-induced oxidative damage and matrix metalloproteinases expression in mouse skin. J Invest Dermatol. 2004 Jun;122(6):1480-7.
23. Yanagawa Y, Yamamoto Y . A combination effect of epigallocatechin gallate, a major compound of green tea catechins, with antibiotics on Helicobacter pylori growth in vitro. Curr Microbiol. 2003 Sep;47(3):244-9.