Green tea as cancer treatment and prevention has been common topic for decades. And hundreds of medical studies have been conducted on it. While some claims are superficial, some are backed up by real medical studies.
Green tea is slightly oxidized during manufacturing, thus keeping intact its curative properties. It is very popular in China and Japan, where it is considered as one of the most effective alternative therapies to fight and prevent many medical conditions such as many cancers. Recently it is spreading more and more in the West, where traditionally people drink black tea instead.
The Anticancer Agent of Green Tea
In almost all anti-cancer diet, green tea occupies a place of excellence because it is the food that contains the most anti-cancer molecules. These anticancer agents are represented by the catechins (flavonoid family) and occupy one third of the weight of tea leaves!
Catechins have the distinction of being able to tackle many of the processes used by cancerous cells to grow. The most powerful and abundant catechin is EGCG (epigallocatechin gallate); it has, in particular, the property to suffocate cancerous cells.
In fact, when cancer cells proliferate to form a small tumor, they must necessarily form, in parallel, a network of blood vessels to be fed and to be able to reproduce. This is called angiogenesis. EGCG has the property of preventing development of angiogenesis, which is indispensable for the formation of any malignant tumor and growth. This is one of the most interesting finding in research conducted on green tea and cancer prevention.
However, it role in preventing cancer is somewhat controversial. Although the cell cultures and animal models show that epigallocatechin-3-gallate (EGCG), the main polyphenol found in green tea, has potent anti-inflammatory and anti-proliferative capable of selectively inhibiting cell growth and inducing apoptosis in cancer cells without affecting normal cells, its effectiveness is not fully proven in humans in certain studies, according to some researchers.
Green Tea and Lung Cancer
A study presented January 11, 2010 at a conference sponsored by the American Association for Cancer Research (AACR) and the International Association for the Study of Lung Cancer (IASLC) demonstrated that green tea protect smokers from lung cancer. Dr. Lin Hsin-I, from Chung Shan Medical University in Taiwan, and colleagues recruited 170 people with lung cancer and 340 healthy patients as controls. Participants were questioned about their daily routine: the number of cigarettes smoked, the number of cups of green tea consumed, their dietary intake of fruits and vegetables, cooking methods, and family history of lung cancer. The results show that smokers and nonsmokers who do not drink green tea are five times more likely to develop lung cancer than those who drink at least one cup of green tea per day. Smokers who did not drink green tea are twelve times more likely to be diagnosed with the disease than those who drink at least one cup of green tea per day. Other studies on green tea and lung cancer confirm these findings.
Green Tea and Cancer Prevention
The potential role of green tea in preventing cancer is of great interest in the scientific community. This interest was first motivated by epidemiological studies suggesting an association between green tea and cancer prevention, certain cancers. Subsequently, studies in animal models have shown that catechins are capable of inhibiting the growth of cancerous cells in certain organs such as breast, lung, esophagus, prostate, liver, and skin. There are, however, few clinical studies to corroborate the effects of green tea in humans.
In 2005, following an allegation application for anticancer properties of green tea, the Food and Drug Administration (FDA) stated that there was no scientific evidence of an effect of tea green on the following cancers: colon, rectum, stomach, lung, pancreas, and ovaries. For breast and prostate, the FDA came to the conclusion that its preventive effect is very unlikely.
Green Tea and Endometrial Cancer
In 2009, a meta-analysis of epidemiological studies showed a correlation between green tea and endometrial cancer; regular consumption reduces the risk considerably. The authors of the study, however, draw attention to the fact that the number of studies on the subject is low and the amount of green tea used is difficult to quantify. Another study published the same year found the same results, an association between green tea consumption (5-6 cups per week or daily cup) and reduced risk (23%) of endometrial cancer.
Green Tea and Ovarian Cancer
There are few studies on Green Tea and Ovarian Cancer. However, it is found that women who drink at least two cups per day have at least 46% less risk for developing ovarian cancer. This observation was also reported in another study published in 2002.
Green Tea and Prostate Cancer
The link between green tea and prostate cancer prevention is still difficult to assess. Some population studies show a correlation between reduced risk and increased tea consumption. Others conclude that this is not the case. The results of clinical studies are still few, though promising. Volunteers with BPH at risk of cancer evolution took 600 mg tea catechins daily for one year. At the end of treatment, the rate of cancer was diagnosed only 3% instead of 30% in the control group. There are more studies being conducted on Green Tea and Prostate Cancer; hopefully more light will be shed.
Green Tea and Breast Cancer
The data on green tea and breast cancer are mainly epidemiological and few. They suggest that tea consumption may reduce the risk of breast cancer occurrence and limit its recurrence. The effect would observe from 3 to 5 cups per day. Other studies suggest that the practice does not reduce the risk of breast cancer among Asian women however. Research on Green tea and breast cancer prevention is highly controversial. While the big companies claim there is no real proof the practice really helps women avoiding the disease other independent studies claim completely otherwise.
Green Tea and Esophageal Cancer
Epidemiological studies have also shown that consumption of 2 to 3 cups of tea per week, from February to March, reduces the risk of esophageal cancer. This effect is especially found in women. However, the results of these studies have been contradicted by another study on Green Tea and Esophageal Cancer performed on people with precancerous lesions of the esophagus. After consuming 5 mg tea extract daily for 11 months, no improvement in the condition of the lesion has been shown.
Green Tea and Oral Cancer
A preliminary study suggests that consumption of green tea extract, precisely 3 times daily after meals, for 12 weeks, helps prevent cancer of the mouth, compared to placebo. This clinical study conducted on 39 participants at risk of cancer of the mouth is confirmed by a study of greater magnitude on green tea and mouth cancer.
- Heiss, Mary Lou; Heiss, Robert J. (2007),The Story of Tea: A Cultural History and Drinking Guide, Ten Speed Press, pp. 179–185, ISBN 1-58008-745-0
- Lin YW, Hu ZH, Wang X, Mao QQ, Qin J, Zheng XY, Xie LP (February 2014).“Tea consumption and prostate cancer: an updated meta-analysis”. World J Surg Oncol (Meta-Analysis) 12: 38. doi:10.1186/1477-7819-12-38. PMC 3925323. PMID 24528523.
- Hou IC, Amarnani S, Chong MT, Bishayee A (June 2013).“Green tea and the risk of gastric cancer: epidemiological evidence”. World J Gastroenterol (Review) 19 (24): 3713–22. doi:10.3748/wjg.v19.i24.3713. PMC 3699047. PMID 23840110
- Zheng XX, Xu YL, Li SH, Liu XX, Hui R, Huang XH (August 2011).“Green tea intake lowers fasting serum total and LDL cholesterol in adults: a meta-analysis of 14 randomized controlled trials”. Am J Clin Nutr (Meta-Analysis)94 (2): 601–10.doi:10.3945/ajcn.110.010926. PMID 21715508.
- Green Tea Consumption and Mortality Due to Cardiovascular Disease, Cancer, and All Causes in Japan, S Kuriyama, T Shimazu, K Ohmori, N Kikuchi, N Nakaya, Y Nishino, Y Tsubono, I Tsuji, JAMA. 7. Boehm K, Borrelli F, Ernst E, Habacher G, Hung SK, Milazzo S, Horneber M, Green tea (Camellia sinensis) for the prevention of cancer [ archive] , Cochrane Database of Systematic Reviews, 2009, Issue 3. Art. No.: CD005004. DOI: 10.1002/14651858.CD005004.pub2
- Boon HS, Olatunde F, Zick SM,Trends in complementary/alternative medicine use by breast cancer survivors: comparing survey data from 1998 and 2005 [ archive], BioMed Central Womens Health, 2007;7:1-7
- Lin I-H, Ho M-L, Chen H-Y, Lee H-S, Huang C-C, et al. (2012),Smoking, Green Tea Consumption, Genetic Polymorphisms in the Insulin-Like Growth Factors and Lung Cancer Risk [ archive] . PLoS ONE 7(2): e30951. doi:10.1371/journal.pone.0030951
- Parkin DM, Bray F,et al. Global cancer statistics, 2002. CA Cancer J Clin. 2005 Mar-Apr;55(2):74-108.
11. Yang CS, Wang X, et al. Cancer prevention by tea: animal studies, molecular mechanisms and human relevance. Nat Rev Cancer. 2009 Jun;9(6):429-39. Review.
12. Kurahashi N, Sasazuki S, et al; Green tea consumption and prostate cancer risk in Japanese men: a prospective study. JPHC Study Group. Am J Epidemiol. 2008 Jan 1;167(1):71-7. Epub 2007 Sep 29.
13. Jian L, Xie LP, et al. Protective effect of green tea against prostate cancer: a case-control study in southeast China. Int J Cancer. 2004 Jan 1;108(1):130-5.
14. Kikuchi N, Ohmori K, et al. No association between green tea and prostate cancer risk in Japanese men: the Ohsaki Cohort Study. Br J Cancer. 2006 Aug 7;95(3):371-3. Epub 2006 Jun 27.
15. Bettuzzi S, Brausi M, et al. Chemoprevention of human prostate cancer by oral administration of green tea catechins in volunteers with high-grade prostate intraepithelial neoplasia: a preliminary report from a one-year proof-of-principle study. Cancer Res. 2006 Jan 15;66(2):1234-40.
16. Seely D, Mills EJ, et al. The effects of green tea consumption on incidence of breast cancer and recurrence of breast cancer: a systematic review and meta-analysis. Integr Cancer Ther. 2005 Jun;4(2):144-55. Review.
17. Sun CL, Yuan JM, et al. Green tea, black tea and breast cancer risk: a meta-analysis of epidemiological studies. Carcinogenesis. 2006 Jul;27(7):1310-5. Epub 2005 Nov 25.
18. Ogunleye AA, Xue F, Michels KB. Green tea consumption and breast cancer risk or recurrence: a meta-analysis. Breast Cancer Res Treat. 2010 Jan;119(2):477-84. Epub 2009 May 13. Review.
19. Gao YT, McLaughlin JK, et al. Reduced risk of esophageal cancer associated with green tea consumption. J Natl Cancer Inst. 1994 Jun 1;86(11):855-8.
20. Sun CL, Yuan JM, et al. Urinary tea polyphenols in relation to gastric and esophageal cancers: a prospective study of men in Shanghai, China. Carcinogenesis. 2002 Sep;23(9):1497-503.
21. Wang LD, Zhou Q, et al. Intervention and follow-up on human esophageal precancerous lesions in Henan, northern China, a high-incidence area for esophageal cancer. Gan To Kagaku Ryoho. 2002 Feb;29 Suppl 1:159-72.
22. Tang NP, Li H, et al. Tea consumption and risk of endometrial cancer: a metaanalysis. Am J Obstet Gynecol. 2009 Dec;201(6):605.e1-8. Epub 2009 Sep 20.
23. FDA US Food and Drug Administration. Food – Labeling and Nutrition – Letter Responding to Health Claim Petition dated January 27, 2004: Green Tea and Reduced Risk of Cancer Health Claim (Docket number 2004Q-0083) (Docket number 2004Q-0083). [Consulté le 2 juin 2010]. www.fda.gov.
24. Taubert D, Roesen R, Schömig E. Effect of cocoa and tea intake on blood pressure: a meta-analysis. Arch Intern Med. 2007 Apr 9;167(7):626-34.
25. Santé Canada. Médicaments et produits de santé – Extraits de thé vert. Gouvernement du Canada. [Consulté le 2 juin 2010]. www.hc-sc.gc.ca.
26. Santé Canada. Médicaments et produits de santé – Bulletin canadien des effets indésirables. Gouvernement du Canada. [Consulté le 2 juin 2010]. www.hc-sc.gc.ca.
27. u K, Gray MA, Oliver C, Liley DT, Harrison BJ, Bartholomeusz CF, Phan KL, Nathan PJ. The acute effects of L-theanine in comparison with alprazolam on anticipatory anxiety in humans. LHum Psychopharmacol. 2004 Oct;19(7):457-65.
28. Nobre AC, Rao A, Owen GN. L-theanine, a natural constituent in tea, and its effect on mental state. Asia Pac J Clin Nutr. 2008;17 Suppl 1:167-8.
29. Kimura K, Ozeki M, Juneja LR, Ohira H. L-Theanine reduces psychological and physiological stress responses. Biol Psychol. 2007 Jan;74(1):39-45.
30. Rowe CA, Nantz MP, et al. Specific formulation of Camellia sinensis prevents cold and flu symptoms and enhances gamma,delta T cell function: a randomized, double-blind, placebo-controlled study. J Am Coll.Nutr 2007;26(5):445-452.
31. Zheng, X. X., Xu, Y. L., Li, S. H., Liu, X. X., Hui, R., and Huang, X. H. Green tea intake lowers fasting serum total and LDL cholesterol in adults: a meta-analysis of 14 randomized controlled trials. Am.J.Clin.Nutr. 2011;94(2):601-610. View abstract.
32. Kim, A., Chiu, A., Barone, M. K., Avino, D., Wang, F., Coleman, C. I., and Phung, O. J. Green tea catechins decrease total and low-density lipoprotein cholesterol: a systematic review and meta-analysis. J.Am.Diet.Assoc. 2011;111(11):1720-1729. View abstract.