Green Tea Helps Boost the Immune System and Cardiovascular Health

By David N. Ilfeld, M.D.
Board Certified in Internal Medicine, Rheumatology, Allergy & Immunology, & NSI Scientific Advisory Board Member

09/27/2007

After water, black or green tea is the most common beverage in the world. Green tea is one of the foods with the highest antioxidant activity. The antioxidant polyphenols in green tea are classified as catechins and the major and most active is called epigallocatechin gallate (EGCG). When fermented, green tea becomes black tea and has less antioxidants as well as somewhat different antioxidants. Beneficial antioxidant polyphenols make up roughly 30-40% of green tea, as opposed to only 3-10% of black tea. In vitro and animal studies show that EGCG from green tea can block the development of cancer by modulating cell proliferation, transformation, inflammation, suicide (apoptosis), invasion and metastasis. Regarding human studies, meta-analysis of epidemiological studies (statistically combining together many separate epidemiological studies) indicates that drinking five or more cups of green tea a day shows a non-statistically significant trend towards the prevention of breast cancer development1.

There was an interesting observation in a study of Chinese, Japanese and Filipino women in Los Angles County. Both green tea and soy had significant, independent protective effects on breast cancer risk. The benefit of green tea was primarily observed for women who were low soy consumers. Similarly, the protective effect of soy was primarily observed among women who were non-drinkers of green tea2. Meta-analysis of epidemiological studies has shown that drinking many cups of green tea daily may perhaps have a preventive effect on the development of colon cancer3. A Japanese study showed no relationship between drinking green tea and the risk of cancer mortality4. Meta-analysis of epidemiological studies of black tea has shown no effect on the development of breast cancer or colon cancer2,3. Thus green tea may possibly prevent the development of some types of cancer, though the evidence is not yet clear.

Tea may have an effect on precancerous abnormalities. A double-blind, intervention trial was done in patients with oral mucosa leukoplasia, which can often develop into oral cancer. Mixed tea given orally and topically for six months resulted in the size of the oral lesions decreasing by 38% whereas the oral lesions decreased in size by 10% in the control group5. In women with human papilloma virus infected cervical lesions, green tea extracts topically and/or orally gave a 69% response rate whereas untreated controls had a 10% response rate6. A double-blind study of men with high-grade prostate intraepithelial neoplasia reported that, after one year, only one prostate cancer was diagnosed among the 30 men treated by swallowing 600 mg of green tea extract per day, whereas nine prostate cancers were found among the 30 placebo-treated men7. These three small interventional studies raise the possibility that green tea extract may be useful in blocking the development of cancer from precancerous lesions.

Epidemiological studies show a much stronger and more striking effect for drinking tea on reducing the risk of cardiovascular disease and cardiovascular mortality. Regarding primary prevention for healthy people, drinking green or black tea has been shown to protect from heart attacks. For example, a Dutch study reported an inverse association of drinking two or more cups of tea with heart attacks with a 32% reduction of non-fatal heart attacks and a 70% reduction of fatal heart attacks8. Similarly, an American study reported that drinking tea was associated with a 44% reduction of heart attacks9. Regarding secondary prevention, after a heart attack, 1,900 American patients were followed for an average of four years. Tea drinkers of less than 14 cups per week had a 31% decreased risk of death and tea drinkers of 14 cups or more per week had a 39% decreased risk of death as compared to non-tea drinkers10. Tea has also been reported to be associated with a reduced risk for stroke. A Chinese study reported that drinking green tea was related to a 65% reduction in the risk of stroke11. 

A Japanese study reported that drinking five cups or more of green tea daily (versus drinking less than five cups of green tea) was associated with more than a 50% reduction in the risk of stroke12. A Dutch study reported that drinking 4.7 cups or more of tea daily (versus less than 2.6 cups of tea) was associated with a 69% risk reduction for stroke13. Drinking tea was reported to be associated with increased risk for coronary heart disease in the United Kingdom and for stroke in Australia; whereas drinking tea was associated with a decreased risk for cardiovascular disease in the rest of the world14. This has led to speculation that perhaps the British custom of drinking black tea together with milk may impair the effect of tea on cardiovascular disease. In summary, drinking two or three cups of tea a day may protect from cardiovascular disease and drinking five or more cups of tea a day may give added cardiovascular protection.

There are several mechanisms of action by which tea may prevent cardiovascular disease. A Japanese, double-blind study of 240 patients with abdominal obesity compared taking a green tea extract with 583 mg of catechins daily versus a control group taking green tea extract with 96 mg of catechins daily for 12 weeks15. Decreases in body weight, waist circumference, hip circumference and subcutaneous fat area were greater in the catechin group than in the control group. For patients who initially had a systolic blood pressure of 130 or more, a greater decrease in systolic blood pressure was observed in the catechin group versus the control group. Furthermore, low density lipoprotein (LDL) cholesterol, also called the "bad cholesterol," was decreased more in the catechin group. In a Chinese, double-blind 12 week study of 240 patients with mild to moderate elevation of cholesterol, green tea extract 375 mg decreased LDL cholesterol by 16%, whereas the placebo group had no significant change in LDL cholesterol16. A third study of patients with mild elevation of cholesterol showed that drinking five cups of black tea daily (versus a placebo beverage with caffeine) reduced LDL cholesterol by 11%17. Thus the apparent reduction of cardiovascular disease by tea may, in part, be due to reduction of LDL cholesterol. Other mechanisms of action which may also, in part, contribute for tea protecting the cardiovascular system include inhibiting oxidation of LDL cholesterol, decreasing inflammation, decreasing platelet aggregation and improving endothelial function so that arteries can improve blood flow. 

In conclusion, drinking green tea and taking green tea extracts in capsules appear to be beneficial. Drinking black tea also has health benefits, though probably less than green tea. I suggest that we all try to drink more tea—especially green tea. I drink one or two cups of green tea per day. Thus if you are like me, you may benefit from also taking supplements of green tea extract. The scientific studies clearly indicate optimal benefits occur at 5 or more cups of tea per day and very few people will or can achieve this without supplements. I recommend you choose a good quality multivitamin or green tea supplement with standardized green tea in the 250–500 mg per day range. Look for 98% polyphenols and 45% EGCG, the primary active components of green tea providing the amazing benefits. There are also some excellent standardized green tea extracts at 250–500 mg per capsule available at Vitacost.com with the most popular being dramatically reduced in price recently. Other products I strongly recommend to patients and family to promote healthy cardiovascular and cellular health include Nutraceutical Sciences Institute® (NSI®) patent pending softgel antioxidant combo TocoQ10 with Japanese pharmaceutical grade coenzyme Q10 in the 200–400 mg per day range along with NSI®'s amazing Mega EFA pharmaceutical grade molecularly distilled super concentrated fish oil at 2–4 softgels per day. One last idea in closing, the studies supporting the health and anti-aging benefits of "universal" water and fat soluble antioxidant alpha lipoic acid at 600 mg per day continue to flood the medical and science journals.

1. Seely D, Mills EJ, Wu P, Verma S and Guyatt GH, 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., June 2005; 4(2): 144-155.
2. Wu AH, Yu M, Tseng CC, Hankin J and Pike MC, Green tea and risk of breast cancer in Asian Americans, Int J Cancer,September 2003; 106(4): 574-579.
3. Sun CL, Yuan JM, Koh WP and Yu MC, Green tea, black tea, and colorectal cancer risk: a meta-analysis of epidemiologic studies, Carcinogenesis. July 2006; 27(7): 1301-1309.
4. Kuriyama S, Shimazu T, Ohmori K, Kikuchi N et al. Green tea consumption and mortality due to cardiovascular disease, cancer, and all causes in Japan: the Ohsaki study, JAMA,September 2006; 296(10): 1255-1265.
5. Li N, Sun Z, Han C and Chen J, The chemopreventive effects of tea on human oral precancerous mucosa lesions, Proc Soc Exp Biol Med, April 1999; 220(4): 218-224.
6. Ahn WS, Yoo J, Huh SW, Kim CK et al., Protective effects of green tea extracts (polyphenon E and EGCG) on human cervical lesions, Eur J Cancer Prev,October 2003; 12(5): 383-390.
7. Berttuzzi S. Brausi M, Rizzi F, Castagnetti G, Peracchia G and Corti A, 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.,January 2006; 66(2): 1234-1240.
8. Geleijnse JM, Launer LJ, Van der Kiup DA, Hofman A and Witteman JC, Inverse association of tea and flavonoid intakes with incident myocardial infarction: the Rotterdam Study, Am J Clin Nutr. May 2002; 75(5): 880-886.
9. Sesso HD, Gaziano JM, Buring JE and Hennekens CH, Coffee and tea intake and the risk of myocardial infarction, Am J Epidemiol,January 1999; 149(2): 162-167.
10. Mukamal KJ, Maclure M, Muller JE, Sherwood JB and Mittleman MA, Tea consumption and mortality after acute myocardial infarction, Circulation. May 2002; 105(21): 2476-2481.
11. Chen Z, Li Y, Zhao LC, Zhou BF et al., A study on the association between tea consumption and stroke, Zhonghua Liu Xing Bing Xue Za Zhi. August 2004; 25(8): 666-670.
12. Sato Y, Nakatsuka H, Watanabe T, Hisamichi S et al., Possible contribution of green tea drinking habits to the prevention of stroke, Tohoku J Exp Med,April 1989; 157(4): 337-343.
13. Keli SO, Hertog MG, Feskens EJ and Kromhout D, Dietary flavonoids, antioxidant vitamins, and incidence of stroke: the Zutphen study, Arch Intern Med. March 1996; 156(6): 637-642.
14. Peters U, Poole C and Arab L. Does tea affect cardiovascular disease? A meta-analysis, Am J Epidemiol,September 2001; 154(6): 495-503.
15. Nagao T, Hase T and Tokimitsu I, A green tea extract high in catechins reduces body fat and cardiovascular risk in humans, Obesity,June 2007; 15(6): 1473-1483.
16. Maron DJ, Lu GP, Cai NS, Wu ZG et al., Cholesterol-lowering effect of a theaflavin-enriched green tea extract: a randomized controlled trial, Arch Intern Med,June 2003; 163(12): 1448-1453.
17. Davies MJ, Judd JT, Baer DJ, Clevidence BA et al., Black tea consumption reduces total and LDL cholesterol in mildly hypercholesterolemic adults, J Nutr,October 2003; 133(10): 3298S-3302S.