Green Tea Extract
Green Tea Extract (GTE) comes from the dried leaves of the Camellia sinensis plant. It has numerous potential health benefits and provides a natural stimulant (caffeine). Additionally, green tea has shown to be thermogenic, which helps to increase body temperature and burn calories (references 78, 89).
GTE is taken to help support immune function, mental alertness, cardiovascular health and fat loss (references 6, 9, 10). Studies have also shown that consuming up to 2500 mg of GTE catechins daily for 24 weeks may reduce the total cholesterol (references 12, 13), and more specifically, the “bad” cholesterol (low-density lipoprotein). Green tea contains 2% to 4% caffeine, which affects thinking and alertness (for further information on caffeine, please refer to the write-up). Additionally, there is early research suggesting that taking certain green tea pills improves some breathing tests during exercise in healthy adults.
GTE is thought to be safe when taken at appropriate doses for periods of up to two years. Some people experience upset stomachs and constipation. In rare cases GTE may cause liver problems. In high dosages, GTE may be unsafe due to the caffeine content. These side effects can range from mild to serious and include headache, nervousness, sleep problems, vomiting, diarrhea, irritability, irregular heartbeat, tremor, heartburn, dizziness, ringing in the ears, convulsions, and confusion. Dosages above 10 grams may be lethal (references 1, 5).
Children or women who are pregnant or breast-feeding can consume GTE, but should limit the dosage to less than 200mg per day.
Using fish oil and quercetin have been shown to exert synergistic benefits and help increase green tea's bioavailability (reference 14). Green tea catechins also appear to be synergistic with L-theanine in regards to alleviating cognitive decline in animal studies (reference 11). On the other end of the spectrum, green tea should not be consumed in combination with stimulant drugs (i.e. amphetamines, cocaine, ephedrine).
Dosages of GTE are highly dependent on the standardized composition of the catechin epigallocatechin gallate (aka EGCG). Studies have shown that 400-500 milligrams of EGCG per day may provide some fat-burning benefits. 50-1600 (reference 3, 4) milligrams is generally considered safe to consume daily (reference 15); taking into account a person’s age, diet and weight being the determining factor of the upper daily limit. Due to the way in which GTE is absorbed in the body, consuming on an empty stomach allows for greater efficacy (reference 2).
1. Park YS, et al Comparison of the nutrient and chemical contents of traditional Korean Chungtaejeon and green teas . Plant Foods Hum Nutr. (2010)
2. Chen L1, et al Absorption, distribution, elimination of tea polyphenols in rats . Drug Metab Dispos. (1997)
3. Lambert JD1, et al Epigallocatechin-3-gallate is absorbed but extensively glucuronidated following oral administration to mice . J Nutr. (2003)
4. Isozaki T, Tamura H Epigallocatechin gallate (EGCG) inhibits the sulfation of 1-naphthol in a human colon carcinoma cell line, Caco-2 . Biol Pharm Bull. (2001)
5. Henning SM, et al Bioavailability and antioxidant effect of epigallocatechin gallate administered in purified form versus as green tea extract in healthy individuals . J Nutr Biochem. (2005)
6. Hong J, et al Involvement of multidrug resistance-associated proteins in regulating cellular levels of (-)-epigallocatechin-3-gallate and its methyl metabolites .Biochem Biophys Res Commun. (2003)
7. 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)
8. Derdemezis CS, et al Effect of Plant Polyphenols on Adipokine Secretion from Human SGBS Adipocytes . Biochem Res Int. (2011)
9. Seifert JG, et al Effect of acute administration of an herbal preparation on blood pressure and heart rate in humans . Int J Med Sci. (2011)
10. Wang H, et al Effects of catechin enriched green tea on body composition . Obesity (Silver Spring). (2010)
11. Lu K, et al The acute effects of L-theanine in comparison with alprazolam on anticipatory anxiety in humans . Hum Psychopharmacol. (2004)
12. Koo SI, Noh SK Green tea as inhibitor of the intestinal absorption of lipids: potential mechanism for its lipid-lowering effect . J Nutr Biochem. (2007)
13. Ikeda I, et al Tea catechins decrease micellar solubility and intestinal absorption of cholesterol in rats . Biochim Biophys Acta. (1992)
14. Wang P, Heber D, Henning SM Quercetin Increased the Antiproliferative Activity of Green Tea Polyphenol (-)-Epigallocatechin Gallate in Prostate Cancer Cells .Nutr Cancer. (2012)
15. Ullmann U, et al A single ascending dose study of epigallocatechin gallate in healthy volunteers . J Int Med Res. (2003)