Can drinking green tea make you more healthy?
Read any tea site these days and you’ll find a section dedicated to the health benefits of tea. We’re joining in with our own below. We’ve sifted through mountains of information, buried our selves in stodgy medical abstracts and followed links deep into the far reaches of the internet. Our goal is to be as comprehensive and as up to date as possible. Each time we find new information, written by an authoritative source, we’ll pluck it out and add it here.
This post is about the health benefits of green tea, but we’ll also be preparing dedicated pages for black tea, white tea and oolong tea as all teas offer potent health boosting, anti-inflammatory and anti-oxidative properties. With green tea, most of the excitement centers around a group of tea catechins (also referred to as polyphenols), the most active of which is epigallocatechin-3-gallate (EGCG). You’ll see those letters cropping up in quite a few of the summaries below.
Just quick glance down this page might convince you that tea is the healthiest thing you can drink. But before you get carried away, remember that not all health benefits have been categorically proven. And the health giving polyphenol concentration will depend on the type of tea, the amount you are drinking, the temperature of the water, brew time and so on.
Yes there are many, many upsides to drinking tea. I’m certainly a believer. But I also drink tea for its great taste, and I encourage you to do so too.
Green tea varieties rich in EGCG were shown in a 2007 study conducted by the National Institute of Vegetable and Tea Sciences together with other bodies, to reduce allergies in humans. The tea used in the study was “benifuuki” green tea administered in a double blind clinical study on subjects with Japanese cedar pollinosis. Allergic responses such as blowing the nose and itching eyes “were significantly relieved” compared to the placebo group.
In January 2011, a study published in Phytomedicine indicated that both green and black tea inhibit the activity of enzymes (specifically acetycholinesterase) associated with the development of Alzheimer’s disease. Green tea also obstructs the ability of beta amyloid which plays a role in the formation of protein deposits in the brain and reduces the toxic effect of hydrogen peroxide. (Both hydrogen peroxide and beta-amyloid play a significant role in the development of Alzheimer’s disease). Further tests and clinical trials are needed to provide further support for these findings.
In November 2011 New Scientist published an article describing work carried out at the University of Ulm in Germany where green tea was used in combination with a red laser light to explore a new treatment for Alzheimer’s disease. A green tea extract (known to have beta-amyloid inhibiting characteristics) was administered to brain cells containing beta-amyloid while being stimulated with red light. The beta-amyloid in the cells was reduced by 60%.
A study indicating that green tea may reduce the incidence and severity of rheumatoid arthritis was published in 1998/9 in the Proceedings of the National Academy of Sciences. The study was conducted on mice and found that mice given green tea polyphenols were less susceptible to developing collagen induced arthritis (a form of the disease considered similar to human rheumatoid arthritis).
A 2007 study by the University of Michigan Health System looked into the anti-inflammatory effects of EGCG in green tea and concluded that it may provide therapeutic benefits to people with rheumatoid arthritis. Additional studies are underway.
A NCCAM funded study examining the effects of green tea polyphenols on rheumatoid arthritis in rats found the severity of the disease to be significantly reduced compared to the control group. The researchers recommended that green tea should be further explored as a dietary therapy for use in combination with conventional treatments for the disease.
A 2009 study published in the Journal of Agricultural and Food Chemistry looked at the effects of three tea catechins (EGC, GC and GCG) on bone metabolism. The study was conducted on rat cell cultures. The study concluded that EGC in particular has a positive effect on bone metabolism (by promoting oesteoblastic activity and inhibiting osteoclast differentiations).
Dozens of studies have been conducted to try to determine the link between tea and cancer prevention. The key biological activities being explored include:
(a) free radical scavenging activity by EGCG which may protect cells from DNA damage, (b) inhibition of tumor cell proliferation and invasiveness as a result of action by tea polyphenols, (c) activation of certain detoxification enzymes, and (d) ultraviolet radiation damage protection due to antioxidant activity. Although some studies show a compelling link between tea and cancer prevention, organizations such as the National Cancer Institute consider the results to be inconclusive. Most experts agree that more clinical trials are still needed.
Mechanisms of cancer prevention by tea constituents; In Journal of Nutrition 2003
Chemoprevention of oral cancer by green tea; Via PubMed 2002
Effect of increased tea consumption on oxidative DNA damage among smokers; Jnl of Nutrition 2003
Chemoprevention of Human Prostate Cancer by Green Tea Catechins; European Association of Urology
Over view of Studies; By the National Cancer Institute
A meta analysis (combined study) examining the relationship between tea consumption and several different cardiovascular diseases found the incidence of heart attack (myocardial infarction) to decrease by 11% with an increase in tea consumption of 3 cups per day. However little causation was found with other cardiovascular diseases including stroke and coronary heart disease.
A large 2006 study looking at over 40,530 Japanese adults aged 40-79 over an 7-11 year period reported that cardiovascular related mortality fell 26% and all-cause mortality rates fell by 16% among those consuming 5 or more cups of green tea daily.
Studies have suggested that EGCG in green tea may have a vasodilatory effect (improving endothelial function in humans with coronary artery disease) which may help explain why some epidemiological studies demonstrate a relationship between green tea consumption and a reduction in cardiovascular risk.
According to Vanderbilt University, a 2003 clinical trial conducted in China represents the first human study to find that a tea product lowers cholesterol. The double blind study examined 240 men and women with high cholesterol over a 12 week period who were randomly chosen to receive either a placebo or a capsule containing green and black tea extracts together with the antioxidant theaflavin. A 16 percent reduction in LDL cholesterol was reported.
A randomized trail involving more than 1,400 adults published in 2011 in the Journal of The American Dietetic Association and conducted by the University of Health Sciences College of Pharmacy in California found that drinking green tea daily may help reduce LDL cholesterol and total cholesterol.
A 2010 study involving 14 randomized controlled trials with 1136 subjects published in the American Society for Nutrition found that green tea intake lowers serum total and LDL cholesterol in adults.
A study conducted by Japanese scientists published in the Annals of Internal Medicine looked at the relationship between tea consumption and the risk for diabetes. 25 communities across Japan participated comprising over 17,000 individuals over 40 years of age. After the five year follow up the researchers found that participants with higher green tea consumption were less likely to develop arthritis. Although the relationship appears credible, the results were self-reported so may suffer inaccuracies.
A widely cited Japanese study published online by BMC Pharmacology conducted in 2004 concluded that green tea has “an antidiabetic effect.” A certain serum protein was found to be involved with the antihyperglycemic effect of green tea. The researchers called for more studies to explore the activity of the protein in more detail.
A report published in the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology conducted by researches in Japan indicated that green tea extract can improve exercise endurance by 8-24%. The same report indicates a higher rate of fat oxidation and lower respiratory quotients. The study was conducted on mice so commentators stress caution when extrapolating to humans.
In 2010 a report appearing in the Journal of Agricultural Food and Chemistry raised the possibility that green tea may help protect the eye against glaucoma and other common diseases. The study demonstrated that the antioxidant catechins from tea were able to be absorbed into eye tissues and reduce oxidative stress.
According to research published in Immunology Letters in 2011 by the Linus Pauling Institute at Oregon State University, the action of the polyphenol EGCG in green tea may help increase the number of “regulatory T” cells that support immune function and suppression of autoimmune diseases.
A study conducted by the Harvard Based Brigham and Women’s Hospital (published online by PNAS) indicated that the compound L-Theamine (an amino acid found in tea) improved immune response and disease fighting capacity of T cells. After a four week trial of 11 coffee drinkers and 10 tea drinkers, the researchers found elevated levels of antibacterial proteins in the tea drinkers.
According to the University of Maryland Medical Center, clinical studies indicate that men drinking 10 cups of tea a day are less likely to develop liver problems. The findings have been backed up by animal studies showing that green tea helps protect mice from liver tumors.
A 2005 study conducted at the University of San Francisco and presented at the American Academy of Dermatology found that a cream extract from green tea helps reduce rosacea. The cream, was tested on 60 women with visible symptoms of rosacea. The green tea extract resulted in “significantly fewer” facial inflammatory lesions than placebo treatment.
Theanine (or L-Theanine) is known for its benefits as a relaxant. It generates alpha-waves in the brain which are emitted when the brain is in a relaxed state. Theanine also suppresses the stimulant function of caffeine so that a high quality green tea can make you relax (in an alert, productive way) even though it contains caffeine.
According to NYU Langone Medical Center EGCG, the antioxidant found in green tea can help protect against skin inflammation and carcinogenesis caused by exposure to UVB. They cite studies published by Photochem Photobiol looking into the effects.
Tooth decay and throat infection
A Pace University study presented to the American Society for Microbiology indicates that green tea can help destroy bacteria and viruses that cause throat infections and tooth decay.
Long term, large scale trials are needed to more accurately determine whether tea consumption can promote weight loss or prevent weight regain after weight loss. Animal model studies by the Laboratory of Cancer Research in New Jersey which indicate a lessening of tissue fat in mice drinking green tea, black tea or a caffeine solution are certainly of interest, but when combined with inconsistent results from small human trials, it’s still too early to point to a direct causal link. Studies analyzing the effects of green tea on raising metabolic rates and speeding up fat oxidation seem to be the most compelling but not all researchers are convinced by these effects.