The health benefits of the tea leaf Camellia sinensis are derived from a group of phytochemicals known as polyphenols. Polyphenols in fresh green tea leaves are present as a series of chemicals called catechins. The dominant and most biologically active among the catechins, (-)-epigallocatechin-3-gallate (EGCG), has been shown to induce expression of glutathione S-transferase, glutathione peroxidase, glutamate cysteine ligase, heme oxygenase-1, and other enzymes that protect a variety of cells, including cultured neurons, against oxidative stress-induced cell death. EGCG modulates the redoxsensitive transcription factor Nrf2, which plays a key role in activating detoxifying enzyme HO-1, as well as other phase II enzymes.[1-7] *
Green Tea Leaf Extract
Green tea polyphenols protect erythrocytes (red blood cells) from oxidative stress. In research studies, EGCG supported healthy insulin activity, protected the pancreatic cells by reducing undesirable cytokines (e.g., interleukin-1 beta), and reduced interferon-gamma–induced nitric oxide production—an excess of which may cause free radical damage. Furthermore, it was found that the polyphenols triggered genes that inhibit activation of NF-kappaB and reduced the level of messenger RNA for the hepatic gluconeogenic enzymes, which convert non-carbohydrate sources into glucose. EGCG has been shown to support healthy immune function, support the endocrine system, and promote fat oxidation beyond what would be explained by its caffeine content.*
Many of the wide range of health benefits derived from green tea are dose-dependent, and most Americans are not willing to consume the necessary 5-10 cups of tea a day to gain its advantages. Careful processing of the tea into an extract highly concentrates the key beneficial constituents. Each 600 mg capsule of Green Tea Extract contains 80% polyphenols, 60% catechins, and 30% EGCG. This is equivalent to approximately 10 cups of green tea. Each capsule contains 36-45 mg of caffeine per serving, roughly the equivalent of a can of cola and less than the 95-200 mg of caffeine in an 8-oz cup of brewed coffee. Naturally occurring caffeine in green tea is believed to act synergistically with the polyphenols.
In summary, green tea’s benefits are based upon four actions:
- It is a powerful antioxidant that protects against DNA damage
- It induces detoxifying enzymes
- It supports gene signaling, which helps regulate cellular growth, development, and apoptosis
- It selectively improves the function of the intestinal bacterial flora.
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- Matsunaga K, Klien TW, Friedman H, et al. Legionella pneumophila replication in macrophages inhibited by selective immunomodulatory effects on cytokine formation by epigallocatechin gallate, a major form of tea catechins. Infect Immun. 2001 Jun;69(6):3947-53. [PMID: 11349063]
- Dulloo AG, Duret C, Rohrer D, et al. Effi cacy 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):1040-45. [PMID:10584049]
- 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. [PMID: 10698173]
- Wheeler DS, Catravas JD, Odoms K, et al. Epigallocatechin-3-gallate, a green tea-derived polyphenol, inhibits IL-1 beta-dependent proinflammatory signal transduction in cultured respiratory epithelial cells. J Nutr. 2004 May;134(5):1039-44. [PMID: 15113942]
- Dudka J, Jodynis-Liebert J, Korobowicz E, et al. Activity of NADPH-cytochrome P-450 reductase of the human heart, liver and lungs in the presence of (-)-epigallocatechin gallate, quercetin and resveratol: an in vitro study. Basic Clin Pharmacol Toxicol. 2005 Aug;97(2):74-9. [PMID: 15998352]
- Townsend PA, Scarabelli TM, Pasini E, et al. Epigallocatechin-3-gallate inhibits STAT-1 activation and protects cardiac myocytes from ischemia/reperfusion induced apoptosis. FASEB J. 2004 Oct, 18(13):1621-3. [PMID: 15319365]
- Rizvi SI, Zaid MA, Anis R, et al. Protective role of tea catechins against oxidation-induced damage of type 2 diabetic erythrocytes. Clin Exp Pharmacol Physiol. 2005 Jan-Feb;32 (1-2):70-5. [PMID: 15730438]
- Anderson RA, Polansky MM. Tea enhances insulin activity. J Agric Food Chem. 2002 Nov;50(24):7182-6. [PMID: 12428980]
- Koyama Y, Abe K, Sano Y, et.al. Effects of green tea on gene expression of hepatic gluconeogenic enzymes in vivo. Planta Med. 2004 Nov;70(11):1100-2. [PMID: 15549673]
- Burzynski SR. Aging: gene silencing or gene activation? Med Hypotheses. 2005;64(1):201-8. [PMID: 15533642]
- Mayo Clinic Staff. Nutrition and healthy eating: Caffeine content for coffee, tea, soda and more. Mayo Clinic. http://www.mayoclinic.com/health/caffeine/ AN01211. Published October 1, 2011. Accessed August 16, 2012.
- Dulloo AG, Seydoux J, Girardier L, et al. Green tea and thermogenesis: interactions between catechin-polyphenols, caffeine and sympathetic activity. Int J Obes Relat Metab Disord. 2000 Feb;24 (2):252-8. [PMID: 10702779]