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Green Tea (Camellia sinensis) |
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What is Green Tea (Camellia sinensis): |
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Green tea is produced from the leaves of the tea plant. It is brewed for its many health benefits. Green tea differs from other varieties of teas in the way the leaves are processed. The leaves are just steamed and dried, but not fermented. As the leaves don’t go through oxidation, green tea retains a higher concentration of natural antioxidants (the polyphenols). Polyphenols are deemed to be more potent antioxidants than vitamin C. Polyphenols reduce damage caused by free radicals, the reactive molecules that play a key role in the aging process, as well as in the incidence of cancer, heart disease, and other degenerative conditions.
Free radicals harm cell proteins and genetic material, which leads to serious health problems. The antioxidants in tea get hold of the free radicals before cell injury occurs. Researchers think that the antioxidants can possibly repair DNA damage brought about by the oxidizing free radicals as well. Green tea has six types of polyphenols, referred to as catechins. It is especially rich in the polyphenol EGCG (epigallocatechin-3-gallate), which has been recognized for its several health protective properties.
Some studies also suggest that green tea could support weight loss by increasing the body’s metabolic rate and reducing body fat.
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History of Green Tea (Camellia sinensis): |
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Green tea has been enjoyed for centuries as a refreshing beverage in Asian culture. It has been used in traditional Chinese medicine for a wide range of health problems - for healing wounds, as a diuretic, to improve resistance, and promote heart health. The Dutch first introduced Green Tea to the West in the 1600’s and tea is now the number one consumed beverage in the world. Since the 1980s Green Tea supplements have become popular in a variety of weight loss and anti-oxidant nutritional supplements.
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Benefits of Green Tea (Camellia sinensis): |
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Green tea can help prevent cancer, and it may control its advancement. Catechins, the antioxidants abundantly present in green tea, counter free radicals before they cause damage that can turn cells cancerous. Catechins have also been found to inhibit cancer initiation and growth process through specific mechanisms.
Population-based studies have linked green tea consumption with lower rates of cancer. The Journal of the National Cancer Institute published the results of an epidemiological study indicating that drinking green tea significantly reduced the risk of developing esophageal cancer in Chinese men and women. Regular consumption of green tea also protects women against breast cancer. Animal studies suggest that green tea checks cancer in its early stages. Catechins in green tea have exhibited the ability to inhibit tumor formation in the intestine and colon. It has been observed that chemically induced tumors decreased in size in mice that were fed green tea. Epigallocatechin-3-gallate has been shown to modulate the inflammatory response in malignant tumor cells in the human colon.
Green tea offers cardiovascular benefits due to the naturally-occurring flavanoids that work as antioxidants. Regular intake of green tea can reduce the risk of suffering a heart attack. Lower incidence of cardiovascular events has been observed in habitual green tea drinkers in Southeast Asian countries. Studies have shown that Green Tea drinkers tend to have lower cholesterol levels.
Green tea could help regulate blood glucose levels, preventing diabetes and the complications connected to diabetes (e.g., cataracts). Catechins in green tea have the ability to block starch and sucrose in the digestive tract. Over a period of three months diabetic rats who consumed green tea showed lower glucose levels when the composition of their blood and eye lenses were assessed.
Preliminary studies indicate that constituents in green tea could help control weight and metabolic conditions associated with obesity. Mice on a high fat diet, when treated with EGCG, showed less weight gain and body fat than those who were not administered the catechin. Results also indicate that mice treated with EGCG had less fat buildup in their livers.
Green tea antioxidants are believed to guard the body against some of the negative effects of aging. The polyphenols in tea possibly limit age-related degeneration of our brain; tea consumption has been associated with lower incidence of dementia, Alzheimer's and Parkinson's diseases. Cellular and animal models of neurological disorders denote that epigallocatechin-3-gallate has a neuroprotective effect. Research suggests green tea impedes enzymes implicated in the accumulation of protein deposits in the brain, which is linked with the development of Alzheimer's disease. Further, results of a study involving mice indicate that over a long-term period, tea catechins could help maintain physical endurance and improve energy metabolism in muscles that tend to atrophy with age.
Research on this subject:
Basu A, Lucas EA. Mechanisms and Effects of Green Tea on Cardiovascular Health. Nutr Rev. 2007 Aug;65(8 Pt 1):361-75.
Bose M, et al. The Major Green Tea Polyphenol, Epigallocatechin-3-Gallate, Inhibits Obesity, Metabolic Syndrome, and Fatty Liver Disease in High-Fat-Fed Mice. J Nutr. 2008 Sep;138(9):1677-83.
Dufresne CJ, Farnworth ER. A Review of Latest Research Findings on the Health Promotion Properties of Tea. J. Nutri Biochem. 2001;12 (7):404-421.
Gao YT, McLaughlin JK, Blot WJ, et al. Reduced Risk of Esophageal Cancer Associated With Green Tea Consumption. J Natl Cancer Inst. 1994 Jun 1;86(11):855–858.
Issa AY, Volate SR, Muga SJ, et al. Green Tea Selectively Targets Initial Stages of Intestinal Carcinogenesis in The AOM-Apc Mouse Model. Carcinogenesis. 2007;28(9):1978–1984.
Mandel SA, Amit T, Kalfon L, et al. Targeting Multiple Neurodegenerative Diseases Etiologies with Multimodal-Acting Green Tea Catechins. J Nutr. 2008 Aug;138:1578S-1583S.
Murase, et al, Tea Catechin Ingestion Combined with Habitual Exercise Suppresses the Aging-Associated Decline in Physical Performance in Senescence-Accelerated Mice. Am J Physiol Regul Integr Comp Physiol. 2008;295:R281-R289.
Porath D, Riegger C, Drewe J, Schwager J. Epigallocatechin-3-gallate Impairs Chemokine Production in Human Colon Epithelial Cell Lines. J Pharmacol Exp Ther. 2005;315:1172–80.
Vinson JA, Zhang J. Black and Green Teas Equally Inhibit Diabetic Cataracts in a Streptozotocin-Induced Rat Model of Diabetes. J Agric Food Chem. 2005;53(9):3710–3713/
Zhang M, Holman CD, Huang J, Xie X. Green Tea and the Prevention of Breast Cancer: A Case-Control Study in Southeast China. Carcinogenesis. 2007;28(5):1074-1078.
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Sources and Forms of Green Tea (Camellia sinensis): |
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Green tea is made from the leaves of Camellia sinensis, a plant native to Asia. It is marketed in the dried leaf form. Green tea is usually brewed with a teaspoon of the dried tea leaves in a cup of hot water or by steeping a tea bag for about 3 to 5 minutes. Steeping releases its catechins.
Green tea extract is also sold as a capsule and as a liquid formulation. Decaffeinated green tea products are available as well. There could be variation in the amount of healthy constituents present in regular and de-caf tea varieties. The flavanol content was found to be lower in the decaffeinated form than in regular tea in one comparison study that assessed different tea products.
However the nutrient loss in the decaf form of tea does depend on the decaffeination process; with a natural method of decaffeination more of the polyphenols are preserved. The manufacturer’s decaffeination method can be ascertained from the label on the tea product packaging.
Henning SM, Fajardo-Lira C, Lee HW, Youssefian AA, Go VL, Heber D. Catechin Content of 18 Teas and a Green Tea Extract Supplement Correlates With the Antioxidant Capacity. Nutr Cancer. 2003;45(2):226-35.
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Recommended Dosage of Green Tea (Camellia sinensis): |
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People in Asian countries typically drink about 3 cups per day which provides approximately 240–320 mg of polyphenols. However there is no definative recommendation as to the optimum intake of green tea.
Researchers have discovered health benefits from drinking 1 to 7 cups of green tea. Even drinking one cup of tea regularly can help lower total cholesterol as seen in a study involving healthy Japanese men in the 40-79 age group. While a review of studies on cardiovascular disease suggests that drinking 7 cups of green tea daily could reduce CHD risk factors through: weight control, improvement in cholesterol levels, inhibition of platelet aggregation (clumping), and moderation of blood pressure.
It has been observed that men in the early stages of prostate cancer who drank 5 or more cups of green tea daily cut their risk of advanced prostrate cancer, versus to non tea drinkers.
Correspondingly, drinking at least a cup of green tea per day may help women with epithelial ovarian cancer survive longer.
While investigating the correlation between green tea intake and fat oxidation it was found that supplementation with 3 capsules of green tea extract, (amounting to a total of 890 ± 13 mg polyphenols and 366 ± 5 mg EGCG) could raise fat oxidation rate in men involved on a moderate-intensity exercise program.
Research on this subject:
Hernández FTT, Rodríguez-Rodríguez E, Sánchez-Muniz FJ. Green tea, a Good Choice for Cardiovascular Disease Prevention? Arch Latinoam Nutr. 2004 Dec;54(4):380-94.
Kurahashi N, Sasazuki S, Iwasaki M, Inoue M, and Tsugane S (for the JPHC Study Group). Green Tea Consumption and Prostate Cancer Risk in Japanese Men: A Prospective Study. American Journal of Epidemiology. 2008;167(1):71-77.
Kuriyama S, Shimazu T, Ohmori K, et al. Green Tea Consumption and Mortality Due to Cardiovascular Disease, Cancer, and All Causes in Japan - The Ohsaki Study. JAMA. 2006;296:1255-65.
Tokunaga S, et al. Green Tea Consumption and Serum Lipids and Lipoproteins in a Population of Healthy Workers in Japan. Annals of Epidemiology. 2002 Apr;12(3):157-165.
Venables MC, Hulston CJ, Cox HR, Jeukendrup AE. Green Tea Extract Ingestion, Fat Oxidation, and Glucose Tolerance in Healthy Humans. American Journal of Clinical Nutrition. 2008 March;87(3):778-784.
Zhang M, Lee AH, Binns CW, Xie X. Green Tea Consumption Enhances Survival of Epithelial Ovarian Cancer. Int J Cancer. 2004 Nov 10;112(3):465-9.
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Safety and Side Effects of Green Tea (Camellia sinensis): |
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Green tea, when taken in excess, can lead to caffeine overload. This can cause headache, irritability, sleeplessness, nausea, dizziness, vomiting, and diarrhea. Side effects associated with caffeine can be avoided by opting for decaffeinated green tea.
Some prescription medications such as warfarin (a blood thinner) can interact unfavorably with green tea. Green tea should be avoided when taking prescribed drugs and over-the-counter pills that contain caffeine or other stimulants. It is best to consult your doctor or pharmacist about possible interactions between green tea and medications recommended to you. Liquid preparations of green tea may contain sugar and/or alcohol. Those with diabetes, alcohol dependence, or liver disease need to be fully aware of all ingredients in green tea formulations.
As it is an herbal product, green tea supplements may contain harmful impurities such as pesticides, arsenic, and heavy metals, so make sure that you use a reliable brand.
Green tea products can interfere with certain medical/laboratory tests such as the chemical stress test, or urine test for calcium. The lab technician and your doctor need to know that you take green tea before undergoing laboratory tests.
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Frequently Asked Questions on Green Tea (Camellia sinensis): |
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Can green tea be used in the treatment or prevention of Cancer?
Green tea as a treatment for preventing or curing cancer continues to be promising. Green tea, with its high EGCG content has the potential to arrest cancer. EGCG activates specific pathways that check growth of malignant cells and keep cancers from spreading. Laboratory studies in cell cultures and animals have shown how the bioactive compound in green tea can be useful in treating cancer.
Researchers at the University of Mississippi Medical Center discovered the effect of EGCG on breast cancer cells in female mice. The findings show that after 5 weeks, the green tea antioxidant decreased tumor size by 66% and weight by 68% in the mice that had ingested EGCG as compared to the tumors in untreated mice. Mice fed the antioxidant also had significantly lower density of small blood vessels within the tumors and lower VEGF protein levels (associated with tumor growth).
Dr. Gu, the senior researcher for the study, theorized EGCG may directly target both tumor blood vessels and tumor cells of breast cancer, leading to the arrest of new blood vessel formation and migration.
It has also been observed that EGCG inhibits cancer through apoptosis, whereby damaged cells self-destruct. A recent study at the MetroHealth Medical Center in Ohio demonstrated that epigallocatechin-3-gallate (EGCG) in green tea can suppress the growth of human pancreatic cancer cells by triggering apoptosis or programmed cell death.
When topically applied, green tea extract can alleviate damage caused by radiation therapy in cancer patients. Green tea extract controls the release of pro-inflammatory cytokines in human white blood cells. Researchers believe that polyphenols and other tea compounds are involved in our body’s anti-inflammatory and anti-bacterial mechanisms.
Clinical trials are underway to further establish the efficacy of green tea in different forms of cancer in humans.
Research on this subject:
Basu A, Haldar S. Combinatorial Effect of Epigallocatechin-3-Gallate and TRAIL on Pancreatic Cancer Cell death. Int J Oncol. 2009 Jan;34(1):281-6.
Jian-Wei G, Young E, et al. Ingredient Found in Green Tea Significantly Inhibits Breast Cancer Growth in Female mice. The American Physiological Society (Press Release). 2008 April 7.
Pajonk F, et al, The Effects of Tea Extracts on Proinflammatory Signaling. BMC Medicine. 2006;4:28.
Can green tea protect against cardiovascular disease?
Green tea is good for the heart. Several mechanisms have been identified that explain its cardiovascular benefits. Green tea improves the health of the endothelial cells that line our arteries. Endothelial cell dysfunction leads to clogging of the arteries and is a critical risk factor for heart disease.
Normally the artery widens as blood supply to the area increases; dilation of the artery as a result of the blood flow is an indicator of endothelial function. People who drink green tea have better blood vessel function as seen in a recent study at Cardiology Department of Athens Medical School. It was observed that within 30 minutes of drinking green tea, volunteers experienced significant widening of their branchial artery, a major blood vessel that traverses from the shoulder to the elbow. Green tea has been found to improve endothelial function even in chronic smokers, and may lower their risk of heart attack.
Green tea supports cardiac health by controlling total cholesterol levels and improving cholesterol profile. It regulates the body’s cholesterol metabolism and lowers cellular cholesterol. Green tea can decrease cholesterol synthesis in whole cells by inhibiting the action of the integral enzyme HMG-CoA reductase. It was observed that green tea extract could affect enzyme activity quite quickly and reduce cholesterol production by 55%.
Green tea antioxidants impede oxidation of low density lipoprotein (LDL) and lowers aortic cholesterol and triglyceride level. Modification of LDL in the arterial wall by oxidation is the first stage in development of atherosclerotic plaque. It eventually leads to arterial blockage and a heart attack. Catechins in green tea can significantly reduce oxidized low density lipoprotein concentration as per findings reported in the International Heart Journal. Study participants who were given 500 mg of catechin (which amounts to about 6 or 7 cups of green tea) showed a marked decrease in oxidized LDL concentration after a period of 4 weeks. What is noteworthy is that these results were achieved without adopting any other lifestyle modification.
Research on this subject:
Alexopoulos, et al. The Acute Effect of Green Tea Consumption on Endothelial Function in Healthy Individuals. European Journal of Cardiovascular Prevention & Rehabilitation. 2008;15(3):300.
Inami S, Takamo M, Yamamoto M, et al. Tea Catechin Consumption Reduces Circulating Oxidized Low-Density Lipoprotein. Int. Heart J. 2007 Nov;48(6):725-32.
Kim W, Jeong MH, et al. Effect of Green Tea Consumption on Endothelial Function and Circulating Endothelial Progenitor Cells in Chronic Smokers. Circ J. 2006 Aug;70(8):1052-7.
Miura Y, Chiba T, et al. Tea Catechins Prevent the Development of Atherosclerosis in Apoprotein E–Deficient Mice. Journal of Nutrition. 2001;131:27-32.
Singh DK, Banerjee S, Porter TD. Green and Black Tea Extracts Inhibit HMG-CoA Reductase and Activate AMP Kinase to Decrease Cholesterol Synthesis in Hepatoma Cells. The Journal of Nutritional Biochemistry. 2008 July (ScienceDirect).
Can green tea aid weight loss?
Green tea can facilitate weight loss. It speeds up our metabolism, helping to burn fat. Administering green tea extract produced a 4% increase in 24 hour energy expenditure as per findings reported in the American Journal of Clinical Nutrition. Findings suggest that constituents in green tea boosts thermogenesis (the inherent rate at which calories are burned), and induces fat oxidation. Researchers noted that subjects who were given only caffeine and no green tea, showed no change in metabolic rates.
Catechins, which occur in large amounts in green tea, can lower body weight, BMI, waist circumference, body fat mass, and subcutaneous fat. Japanese men who drank tea enriched with catechins derived from green tea extract achieved considerable reduction in body fat over a 12 week period. Researchers believe that when taken regularly, catechin-rich tea may be useful in preventing obesity.
While drinking green tea can be safely incorporated into your daily diet, its usage as a weight control supplement needs to be further investigated through long-term studies.
Here are some studies on the above mentioned benefits of green tea.
Research on this subject:
Dulloo AG, Duret C, et al. Efficacy of a Green Tea Extract Rich in Catechin Polyphenols and Caffeine in Increasing 24-h Energy Expenditure and Fat Oxidation in Humans. American Journal of Clinical Nutrition. 1999 Dec;70(6):1040-1045.
Nagao T, Komine Y, et al. Ingestion of a Tea Rich In Catechins Leads To a Reduction in Body Fat and Malondialdehyde-Modified LDL in Men. American Journal of Clinical Nutrition. 2005 Jan;81(1):122-129.
How is green tea different from black and white tea?
Green, black, oolong, and white tea varieties have a common source: leaves of the Camellia sinensis plant. However, in black tea, the crushed leaves are thoroughly fermented during processing. Thus it is dark in color and has a strong flavor. Green tea on the other hand is made from leaves that are dried and steamed, and not allowed to ferment. It has a milder taste and is richer in antioxidants. Oolong tea is made from leaves that are fermented slightly and falls between black and green tea in its polyphenol content.
White tea is pale in color and has a very subtle flavor. It is prepared from buds and immature tea leaves that are minimally processed and do not undergo fermentation. White tea has the highest level of polyphenols compared to other tea varieties. It also happens to be the most expensive of these teas.
Is it better to drink green tea than coffee?
Green tea is rich in polyphenols that are considered to be some of the most powerful antioxidants. As cited in the above research studies, epigallocatechin gallate (the major component in green tea) works on many different levels and through many different mechanisms to protect the body against: cancer, heart disease, diabetes, and metabolic dysfunction. Green tea has exhibited anti-inflammatory and antibacterial properties.
Coffee too has some health benefits. Regular coffee consumption has been associated with lower incidence of certain cancers and gallstones, and is associated with decreased risks of: Type II diabetes and age-related deterioration of cognitive functioning.
In terms of caffeine content, a cup of green tea has about half the amount of caffeine present in a cup of regular coffee.
Research on this subject:
AGA News Release (2002). Harvard Nurses' Health Study: Coffee Lowers Risk of Gallstone Disease in Women.
Inoue M, et al. Influence of Coffee Drinking on Subsequent Risk of Hepatocellular Carcinoma: A Prospective Study in Japan. J Natl Cancer Inst. 2005 Feb 16;97(4):293-300.
van Dam RM, Hu FB. Coffee Consumption and Risk of Type 2 Diabetes. JAMA. 2005;294:97-104.
van Gelder BM, et al. Coffee consumption is Inversely Associated with Cognitive Decline in Elderly European Men: The FINE Study. European Journal of Clinical Nutrition. 2007;61:226–232.
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Additional Research on Green Tea (Camellia sinensis): |
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Green Tea and Cancer
Blot WJ, Chow WH. McLaughlin JK. Tea and cancer: a review of the epidemiological evidence. Eur J Cancer Prev. 1996 Dec;5(6):425-38.
Chen D, Dou QP. Tea polyphenols and their roles in cancer prevention and chemotherapy. Int J Mol Sci. 2008 Jun;9(7):1196-206.
Ji BT, Chow WH, Hsing AW, et al. Green tea consumption and the risk of pancreatic and colorectal cancers. Int J Cancer. 1997 Jan 27;70(3):255-8.
Green Tea and Heart Disease
Tanabe N, Suzuki H, Aizawa Y, Seki N. Consumption of green and roasted teas and the risk of stroke incidence: results from the Tokamachi-Nakasato cohort study in Japan. Int J Epidemiol. 2008 Oct;37(5):1030-1040.
Tinahones FJ, Rubio MA, Garrido-Sanchez L, et al. Green tea reduces LDL oxidability and improves vascular function. J Am Coll Nutr. 2008 Apr;27(2)209-13.
Upaganlawar A, Gandhi C, Balaraman R. Effect of green tea and vitamin e combination in isoproterenol induced myocardial infarction in rats. Plant Foods Hum Nutr. 2009 Mar;64(1):75-80.
Green Tea and Weight Loss
Auvichayapat P, Prapochanung M, Tunkamnerdthai O, et al. Effectiveness of green tea on weight reduction in obese Thais: A randomized, controlled trial. Physiol Behav. 2008 Feb 27;93(3):486-91.
Hsu CH, Tsai TH, Kao YH, et al. Effect of green tea extract on obese women: a randomized, double-blind, placebo-controlled clinical trial. Clin Nutr. 2008 Jun;27(3):363-70.
Hursel R, Westerterp-Plantenga MS. Green tea catechin plus caffeine supplementation to a high-protein diet has no additional effect on body weight maintenance after weight loss. Am J Clin Nutr. 2009 Mar;89(3):822-30.
Maki KC, Reeves RS, Farmer M, et al. Green tea catechin consumption enhances exercise-induced abdominal fat loss in overweight and obese adults. J Nutr. 2009 Feb;139(2):264-70.
Puig T, Relat J, Marrero PF, et al. Green tea catechin inhibits fatty acid synthase without stimulating carnitine palmitoyltransferase-1 or inducing weight loss in experimental animals. Anticancer Res. 2008 Nov-Dec;28(6A):3671-6.
Shixian Q, VanCrey B, Shi J, Kakuda Y, Jiang Y. Green tea extract thermogenesis-induced weight loss by epigallocatechin gallate inhibition of catechol-O-methyltransferase. J Med Food. 2006 Winter;9(4):451-8.
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