Health Benefits of Green Tea?
Next to water, tea is the most widely consumed beverage in the world. Speaking of water, with all of the potential health benefits of green tea, in particular, perhaps we should be putting it in the water? Seriously. Or rather, let’s take a look at some reasons why you should be drinking green tea more often.
Green tea has several purported health benefits some of which suggest possible ergogenic or performance-enhancing effects while others include cancer prevention. People have been consuming green tea for almost 5000 years.
Let’s take a look at some of the potential health benefits of green tea with my review of the current research on green tea or green-tea extract (epigallocatechin-3-gallate; EGCG).
What are the healthy compounds found in green tea?
Green teas contain a variety of compounds that contribute both to its flavor as well as its potential health benefits. Flavinoids found in green tea contribute to its bitter taste and astringency. Of the flavinoids, they are predominately comprised of four different catechins.
Flavanols including quercetin is found in smaller quantities.
Specifically the four different catechins include:
- epigallocatechin gallate (EGCG)
- epigal- locatechin (EGC)
- epicatechin gallate (ECG)
Potential anti-cancer properties of green tea are generally attributed to the presence of these catechins. Green tea actually has a catechin content equated to 30-42% of its dry weight.
Which catechin is found in green tea extract?
Typically, green tea extracts contain the catechin, (epigallocatechin-3-gallate; EGCG). EGCG is the component of green tea which is currently believed to confer much of its health benefits. It’s also the major constituent–accounting for 50-80% of the total catechin content found in green tea.
Green tea vs. Black tea
Green tea and black tea each undergo different processing in their manufacture. Freshly harvested leaves from the plant, Camellia sinensis, are steamed to prevent fermentation. This yields a dry, stable product of green tea.
While black tea is also made from the same plant (Camellia sinesis), it’s made from leaves that are aged rather than from fresh leaves. Approximately 75% of the catechins found in the leaves are converted via the processes of oxidation and partial polymerization. Consequently, black tea only has an approximate 10-12% catechin content by solid extracts–roughly 5-8x less than what is found in green tea.
How does green tea work?
Green tea’s antioxidant activity and its ability to protect against oxidative damage (free radicals) is one of the mechanisms though to confer its health benefits particularly in the prevention of atherosclerosis and cardiovascular disease (Khan N, et al 2007).
As noted by Khan N et al, multiple clinical trials have noted that consumption of a single dose of green tea is followed by an improvement in antioxidant status within 30-60 minutes. This antioxidant effect peaks within 1-2 hours and subsides shortly thereafter.
Researchers believe that green tea and specifically the ECGC catechin may have important anti-cancer properties such as preventing DNA damage and inhibiting tumor cell growth (Zeng J et al, 2011).
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.
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.
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).
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 athletic performance?
Does green tea extract (EGCG) enhance endurance performance in cyclists?
Results from a recent study published in the International Journal of Sports Nutrition and Exercise Metabolism suggests that green tea extract does not offer any additional benefits to caffeine with respect to fat oxidation or endurance (Dean et al, 2009).
The dose of ECGC (green tea extract) used in this study was 270 mg over a 6 day period and 1 hour prior to exercising. Though green tea extract did not improve cycling performance, the study authors did find that 3mg/kg of caffeine supplementation did improve cycling performance.
Green tea and cardiovascular risk?
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).
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%).
Medline Plus – Green Tea
Medline Plus is a very useful reference for summary data on dietary supplements, herbs, and vitamin. The link to their summary data on green tea can be found (here). They have a rating schema of the level of evidence for the effectiveness of green tea for various health conditions as summarized in the following:
Likely effective for:
- Genital warts – There’s actually an FDA-approved green tea extract ointment for treating this condition.
- Increasing Mental Alertness – Due to the caffeine content.
Possibly effective for:
- Orthostatic hypotension
- Preventing bladder, ovarian, esophageal, and pancreatic cancer
- Protection against Parkinson’s disease
- Cervical dysplasia – caused by HPV infection
- Hypotension – Help elderly people who have low blood pressure after eating
- Hyperlipidemia – reducing high levels of cholesterol and triglycerides in blood
Medline Plus Safety concerns:
- More than 5 cups per day can cause side effects due to caffeine
- sleep problems
- irregular heart beat
- Green tea may reduce iron absorption from food
Medline’s Special Precautions:
- Liver disease – Green tea extracts have been linked to several cases of liver damage.
- Osteoporosis – Caffeine found in green tea can lead to increased flushing of calcium in urine.
- Glaucoma – Drinking green tea increases pressure in the eyes which lasts for at least 90 minutes.
- Heart conditions – Green tea may cause an irregular heart beat.
- Diabetes – Green tea consumption may alter blood sugar levels in those who have diabetes.
- Anxiety disorders – Green tea could potentially worsen anxiety symptoms due to caffeine content.
- Anemia – Green tea’s effects on reducing iron absorption could have an adverse effect on those who have been diagnosed with anemia.
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- 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.
- Nagao T, Meguro S, Hase T, Otsuka K, Komikado M, Tokimitsu I, Yamamoto T, Yamamoto K. A catechin-rich beverage improves obesity and blood glucose control in patients with type 2 diabetes. Obesity (Silver Spring). 2009 Feb;17(2):310-7. Epub 2008 Nov 13.
- Nantz MP, Rowe CA, Bukowski JF, Percival SS. Standardized capsule of Camellia sinensis lowers cardiovascular risk factors in a randomized, double-blind, placebo-controlled study. Nutrition. 2009 Feb;25(2):147-54. Epub 2008 Oct 9.
- Brown AL, Lane J, Coverly J, Stocks J, Jackson S, Stephen A, Bluck L, Coward A, Hendrickx H. Effects of dietary supplementation with the green tea polyphenol epigallocatechin-3-gallate on insulin resistance and associated metabolic risk factors: randomized controlled trial. Br J Nutr. 2009 Mar;101(6):886-94. Epub 2008 Aug 19.
- Nagao T, Meguro S, Hase T, Otsuka K, Komikado M, Tokimitsu I, Yamamoto T, Yamamoto K. A catechin-rich beverage improves obesity and blood glucose control in patients with type 2 diabetes. Obesity (Silver Spring). 2009 Feb;17(2):310-7.
- Panagiotakos DB, Lionis C, Zeimbekis A, Gelastopoulou K, Papairakleous N, Das UN, Polychronopoulos E. Long-term tea intake is associated with reduced prevalence of (type 2) diabetes mellitus among elderly people from Mediterranean islands: MEDIS epidemiological study. Yonsei Med J. 2009 Feb 28;50(1):31-8.
- Matsumoto K, Yamada H, Takuma N, Niino H, Sagesaka YM. Effects of green tea catechins and theanine on preventing influenza infection among healthcare workers: a randomized controlled trial. BMC Complement Altern Med. 2011 Feb 21;11:15. PubMed PMID: 21338496; PubMed Central PMCID: PMC3049752.