Green tea has been consumed for thousands of years in some cultures. Recently, clinical studies have bolstered claims of green tea’s benefits for some health conditions, but evidence for others is lacking or contradictory.
Green tea contains 20 to 45 percent polyphenols by weight, of which up to 80 percent are catechins. Catechins—in particular epigallocatechin gallate (EGCG)—are potent antioxidants that serve a variety of protective functions.
Green tea is made by lightly steaming and drying the leaves from the Camellia sinensis plant. This method of preparation distinguishes green tea from other popular kinds of tea (i.e., oolong or black teas), which typically undergo a period of fermentation during processing.
White tea is purported to contain even higher levels of polyphenols than green tea.
Health benefits attributed to green tea include:
Genital and Perianal Warts
- In October 2006, after evaluating the pooled results of two phase III clinical trials, the FDA approved Veregen ointment—a mixture of catechins extracted from green tea—for the treatment of external perianal and genital warts caused by human papillomavirus (HPV). (US Food and Drug Administration. Veregen (kunecatechins) ointment, 15%. http://www.fda.gov/cder/foi/label/2006/021902lbl.pdf and Ahn W, et al. Protective effects of green tea extracts (polyphenon E and EGCE) on human cervical lesions. Eur J Cancer Prev 2003;12(5):383-90)
- Preliminary trials suggest a similar benefit from catechins, alone or in combination with an oral green tea extract, in treating cervical HPV.
Cancer
- A 2006 meta-analysis of epidemiologic studies showed that a high intake of green tea conferred a 20% reduction in the risk of breast cancer in certain populations of women. (Sun C, et al. Green tea, black tea and breast cancer risk: a meta-analysis of epidemiological studies. Carcinogenesis 2006; 27(7):1310-15)
- A similar analysis in the same journal revealed an 18% reduction in the risk of colorectal cancer among persons who consumed large quantities of green tea.
- A Chinese study of over 18,000 men showed that drinkers of green tea had one-half the risk for stomach or esophageal cancer when compared to men who drank little green tea. (Sun C, et al. Urinary tea polyphenols in relation to gastric and esophageal cancers: a prospective study of men in Shanghai, China. Carcinogenesis 2002;23(9):1497-1503)
- Several studies show a decrease in risk of prostate cancer among green tea drinkers. One recent large trial demonstrated a dose-related reduction in advanced prostate cancer among men who drank green tea. (Kurahashi N, et al. Green tea consumption and prostate cancer risk in Japanese men: a prospective study. Am J Epidemiol 2008;167(1):71-7)
- The National Cancer Institute is investigating the utility of green tea formulations as cancer preventives and adjuvant therapies for certain tumors.
Cardiovascular Disease
- Results of trials to evaluate the effects of green tea on cardiovascular disease have been inconsistent. Some studies associate green tea consumption with significant reductions in cholesterol levels, while others do not.
- Epidemiologic studies show reduced mortality from heart attack and stroke with green tea consumption, but the mechanism has not been clarified. Japanese adults who drink more than five cups of green tea daily enjoy significant reductions in risk of cardiovascular death or stroke. (Kuriyama S, et al. Green tea consumption and mortality due to cardiovascular disease, cancer, and all causes in Japan: the Ohsaki study. JAMA 2006;296(10):1255-65)
Weight Loss
- Although some studies show that green tea is useful for weight management, other studies show no effect. No studies demonstrate a persistent weight benefit from consuming green tea. (Schneider C and Segre T. Green tea: potential health benefits. Am Fam Phys 2009;79(7):591-4)
Given the known health benefits of green tea—specifically the polyphenols it contains—more research is needed to further define and expand its role.
