Gerald Hurowitz, M.D.·Published 28 November 2011·7 min read
Key points
The green tea benefits were discovered 4,000 years ago and since then has been considered a wonder drink!
Lung, colon, and liver cancer Epidemiological studies are one way of looking at the potential benefits of green tea.
Green tea’s potential benefits in preventing prostate cancer have arisen from the low incidence of prostate cancer among the Chinese and Japanese–two populations with a high intake of green tea.
Studies on the potential health benefits of green tea pertaining to diabetes have been somewhat conflicting.
The green tea benefits were discovered 4,000 years ago and since then has been considered a wonder drink!
Green tea acts as an antiviral agent. This beverage contains am mineral called fluoride that prevents cavities as well as strengthens tooth enamel. Did you know that drinking a cup of this tea everyday can help reduce plaque formation and bacterial infections in your mouth? This is because this beverage acts as anti-inflammatory agent. Therefore, it maintains a healthy, active metabolism and circulatory system on your body. This proves that this drink is indeed a miracle in a cup!
What happens is that our body utilizes the defensive antioxidant molecules which are present in our system as a response to the negative effects of free radicals. This is done to detoxify the harmful effects.
This is the main reason why health professionals are encouraging you to increase the levels of antioxidants in your body. There are various food available that contains high levels of antioxidants such as fruit and vegetables.
The antioxidant levels of green tea is hundred times more effective than vitamin C and twenty-five times better than vitamin E in protecting our immune systems. Another great reason to drink several cups everyday.
Green tea and cancer risk?
Lung, colon, and liver cancer Epidemiological studies are one way of looking at the potential benefits of green tea. Of note, these types of studies are good for identifying potential associations, but are not as robust of study design as randomized controlled trials.
A prospective cohort study comprised of 8552 individuals in Japan found that drinking more than 10 cups per day of green tea showed a remarkable risk reduction for lung, colon, and liver cancer (Sueoka et al, 2001). Though the study had a large sample size and an 11-year follow-up period, consuming this much green tea is probably not realistic and may have potential side effects due to the caffeine content.
Prostate cancer
Green tea’s potential benefits in preventing prostate cancer have arisen from the low incidence of prostate cancer among the Chinese and Japanese–two populations with a high intake of green tea. Prostate cancer is not only the most commonly diagnosed cancer in American men, but also the second most common cause of cancer death for them. Researchers are actively studying the role of green tea polyphenols in prostate cancer prevention.
Although tea drinking has been associated with health benefits for centuries, only in recent years have its medicinal properties been investigated scientifically. The October issue of Harvard Women's Health Watch recognizes the healthy power of tea while helping readers get the most out of their cups.
Tea's health benefits are largely due to its high content of flavonoids — plant-derived compounds that are antioxidants. Green tea is the best food source of a group called catechins. In test tubes, catechins are more powerful than vitamins C and E in halting oxidative damage to cells and appear to have other disease-fighting properties. Studies have found an association between consuming green tea and a reduced risk for several cancers, including, skin, breast, lung, colon, esophageal, and bladder.
Written and revised by
Gerald Hurowitz, M.D.
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Additional benefits for regular consumers of green and black teas include a reduced risk for heart disease. The antioxidants in green, black, and oolong teas can help block the oxidation of LDL (bad) cholesterol, increase HDL (good) cholesterol and improve artery function. A Chinese study published recently in the Archives of Internal Medicine showed a 46%-65% reduction in hypertension risk in regular consumers of oolong or green tea, compared to non-consumers of tea.
A case-control study conducted in China found that risk of prostate cancer decreased with increasing duration, quantity, and frequency of green tea consumption (Jian L et al, 2004).
As well, a more recent meta-analysis (Zheng J et al, 2011) concluded that green tea consumption may have a protective effect against prostate cancer risk particularly in Asian populations.
Green tea and Diabetes?
Studies on the potential health benefits of green tea pertaining to diabetes have been somewhat conflicting.
Postprandial glucose and insulin RCT
A randomized controlled trial involving 14 healthy volunteers found that consuming 300 ml of green tea with breakfast did not have any glucose or insulin-lowering effects. However, the study did find that increased satiety and fullness was reported after consuming green tea compared to water (Josic J et al, 2010).
Waist circumference, systolic blood pressure, and HBA1C
In contrast to the above study which was done on a single-dose basis in healthy volunteers, researchers in Japan compared the effects of green tea consumption (582.8 mg catechins) vs. control (96.3 g catechins) in those with type 2 diabetes over a 12 week period (Nagao T et al, 2009).
These researchers concluded that green tea may play a role in reducing obesity, helping diabetic maintain a low HbA1c level, and improving insulin secretory ability in diabetics who do not yet require insulin. Of note, the group consuming high doses of catechins lost 3.3 cm from their waist vs. the control (+.1cm). HbA1c was reduced by 0.37 by week 12 vs. control (-.01) though this difference did not reach the level of statistical significance.
Long-term tea consumption and diabetes?
Researchers from Greece published the results of a study that found that moderate tea consumption (1-2 cups per day–either green or black tea) was associated with a 70% lower odds (not risk) of having diabetes when other confounding factors were adjusted for (Panagiotakos DB et al, 2009).
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Green tea and Obesity?
Does green tea catechin consumption enhance fat loss?
A recent study published in the Journal of Nutrition (Maki et al, 2009) found that moderately obese subjects who consumed a beverage containing 625 mg of green tea catechins lost more abdominal fat mass than subjects who consumed a caffeine-only control drink over a 12-week time period. In addition to consuming the beverages, the test subjects and control groups both engaged in a moderate exercise program.
Though both groups lost similar amounts of body fat, the catechin group lost more abdominal fat than the control group.
In yet another study on a catechin containing beverage (582.8 mg of catechins) which was published in the journal, Obesity, the study authors found that it reduced waste circumference and hemoglobin A (1c) levels after 12 weeks (Nago et al, 2009). Adiponectin which is negatively correlated with visceral obesity was significantly higher in the catechin group. All of the subjects in this study had type 2 diabetes but were not receiving insulin therapy.
Green tea and cardiovascular risk?
Cholesterol
Researchers at the University of Florida, Gainesville, published a recent study which study the effects of a decaffeinated green tea capsule on blood pressure, serum lipids, and oxidative stress (Nantz et al, 2009). Results of the study were as follows:
Camellia sinensis (CSC) lowered systolic and diastolic blood pressures by 5 and 4 mmHg, respectively. Blood pressure remained lower for 3 months. 10- and 9-mg/dL reductions in total and low-density lipoprotein (LDL) cholesterol, respectively. CSC lowered serum amyloid-alpha by 42% (a marker of chronic inflammation) and lowered malondialdehyde by 11.9% (a marker of oxidative stress).
Hypertension
A similar study published in the British Journal of Nutrition (Brown et al, 2009) also found that green tea (400 mg EGCG) lowered blood pressure in test subjects while also having a positive effect on their mood.
Green tea in preventing influenza?
Researchers in Japan conducted a randomized controlled trial comparing the efficacy of a green tea supplement (containing 378 mg/d catechins and 210 mg/d of theanine on preventing infection with influenza virus in healthcare workers (Matsumoto K et al, 2011).
The main outcome measure of their study included the incidence of clinically defined influenza infection. Indeed, they found that incidence was lower in the intervention group–4 (4.1%) participants compared to 13 (13.1%) (adjusted OR, 0.25; 95% CI, 0.07 to 0.76, P = 0.022).
However, this preliminary study had a number of limitations including the fact that 93% of the people enrolled in the study were vaccinated for influenza. A slightly higher percentage of those randomized to the catechin group were vaccinated (93.8% vs. 91.9%).
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References:
Khan N, Mukhtar H. Tea polyphenols for health promotion. Life Sci. 2007 Jul 26;81(7):519-33. Epub 2007 Jun 28. Sueoka N, Suganuma M, Sueoka E, Okabe S, Matsuyama S, Imai K, Nakachi K, Fujiki H. A new function of green tea: prevention of lifestyle-related diseases. Annals of New York Academy of Sciences. 2001;928:274–280. Zheng J, Yang B, Huang T, Yu Y, Yang J, Li D. Green tea and black tea consumption and prostate cancer risk: an exploratory meta-analysis of observational studies. Nutr Cancer. 2011;63(5):663-72. Epub 2011 Jun 11. PubMed. PMID: 21667398. Jian L, Xie LP, Lee AH, Binns CW. Protective effect of green tea against prostate cancer: a case-control study in southeast China. International Journal of Cancer 2004. 2004;108(1):130–135. Josic J, Olsson AT, Wickeberg J, Lindstedt S, Hlebowicz J. Does green tea affect postprandial glucose, insulin and satiety in healthy subjects: a randomized controlled trial. Nutr J. 2010 Nov 30;9:63. PubMed PMID: 21118565; PubMed Central PMCID: PMC3002911. Dean S, Braakhuis A, Paton C. The effects of EGCG on fat oxidation and endurance performance in male cyclists. Int J Sport Nutr Exerc Metab. 2009 Dec;19(6):624-44. Maki KC, Reeves MS, Farmer M, Yasunaga K, Matsuo N, Katsuragi Y, Komikado M, Tokimitsu I, Wilder D, Jones F, Blumberg JB, Cartwright Y. Green tea catechin consumption enhances exercise-induced abdominal fat loss in overweight and obese adults. J Nutr. 2009 Feb;139(2):264-70. Epub 2008 Dec 11.
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