All tea plants belong to the same species Camellia sinensis but the varying growing conditions (altitude, climate, soil, etc.) lead to a multitude of distinctive leaves. The way leaves are processed, however, is even more important in developing the individual characteristics of the three predominant types of tea: green, black and oolong.

Green tea is the least processed and thus provides the most antioxidant polyphenols, notably a catechin called epigallocatechin-3-gallate (EGCG), which is believed to be responsible for most of the health benefits linked to green tea. Green tea has the highest concentration of beneficial phytonutrients and the least caffeine of all teas. Drinking green tea has proven to offer medically-tested benefits for human health.

Keeping Bacteria Away

A cup of green tea contains up to 200 mg of catechins, whose biological activity has been mainly attributed to its antioxidant activity. Efficiency of green tea extract in oral hygiene has been known for centuries and this gave researchers a clue that antibacterial activity might be involved.Now researchers from the National institute of Chemistry in Ljubljana, Slovenia discovered that the main ingredients of green tea are able to perform other tricks [1]. They found out that green tea catechins inhibit essential bacterial enzyme DNA gyrase, which is the target of several existing clinically used drugs. By the use of NMR spectroscopy, researchers from Slovenia have now pinpointed the ATP-binding site of DNA gyrase as target of EGCG, the most abundant catechin from the green tea extract. Up to now several compounds targeted against the ATP-binding site of bacteria gyrase have been known but couldn’t be used as drugs due to their side effects on mammalian cells. Lead researcher Roman Jerala, the head of the Laboratory of Biotechnology at NIC explains: “We can anticipate to avoid the problem of toxicity using the compounds based on the green tea catechins, which have centuries of established safety record in the human diet.” This finding may be used to develop even more potent antibacterial compounds.

Protecting from Cardiovascular Disease

According to a new study by scientists at Tohoku University, Japan, regular green tea drinkers have 25% less chance of dying from cardiovascular disease than most other people who are not regular drinkers [2].The study, which began in 1994, looked at 40,530 adults aged 40-79 in North Eastern Japan - a region where green tea is commonly consumed - three quarters of the people drink green tea regularly, most of them have two or three cups a day. At the beginning of the study none of them had a history of stroke, coronary heart disease, or cancer. The researchers monitored these people for 11 years, during which time 4,209 died. During those 11 years 892 died of cardiovascular disease while 1,134 died of cancer. They found that those who consumed five or more cups of green tea a day were 16% less likely to die from any cause than people who consumed one cup or less per day (during those eleven years). The large green tea drinkers’ chance of dying from cardiovascular disease was 26% lower than the one-cup-per-day or less people. No link was found between drinking green tea and higher or lower cancer deaths. The researchers did find, however, that consuming lots of green tea regularly seems to help women more. Women who drank 5+ cups per day were 31% less likely to die from cardiovascular disease compared to the >1 cup-per-day women. Team leader, Dr. Shinichi Kuriyama believes the study shows that green tea consumption may prolong a person’s life by protecting him/her from cardiovascular disease.

Treating Rheumatoid Arthritis

A new study from the University of Michigan Health System suggests that a compound in green tea may provide therapeutic benefits to people with rheumatoid arthritis [3].The study, presented April 29 at the Experimental Biology 2007 in Washington, D.C., looks at a potent anti-inflammatory compound derived from green tea. Researchers found that EGCG inhibited the production of several molecules in the immune system that contribute to inflammation and joint damage in people with rheumatoid arthritis. The compound from green tea also was found to suppress the inflammatory products in the connective tissue of people with rheumatoid arthritis. “Our research is a very promising step in the search for therapies for the joint destruction experienced by people who have rheumatoid arthritis,” says Salahuddin Ahmed, Ph.D., lead researcher on the study. To conduct the research, the scientists isolated cells called synovial fibroblasts from the joints of patients with rheumatoid arthritis. These fibroblasts cells that form a lining of the tissue surrounding the capsule of the joints then were cultured in a growth medium and incubated with the green tea compound. The fibroblasts were then stimulated with pro-inflammatory cytokine IL-10, a protein of the immune system known to play an important role in causing joint destruction in people with rheumatoid arthritis. The researchers looked at whether the green tea compound has the capability to block the activity of two potent molecules, IL-6 and cyclooxygenase-2 (COX-2), which also are actively involved in causing bone erosion in the joints of people with rheumatoid arthritis. When untreated cells were stimulated with IL-10, a sequence of molecular events occurred that resulted in production of the bone-destructive molecules. But the scientist found that pre-incubation with EGCG was capable of inhibiting the production of these molecules. EGCG also inhibited the production of prostaglandin E2, a hormone-like substance that causes inflammation in the joints. The cell signaling pathways that regulate levels of these immune system molecules under both normal and rheumatoid arthritis situations are well studied, and the researchers were able to trace the effects of the green tea compound infusion to see that it worked by inhibiting these pathways. Ahmed says that these studies suggest that EGCG or molecules that could be derived synthetically from the EGCG found in green tea may be of therapeutic value by inhibiting the joint destruction in rheumatoid arthritis.

Preventing HIV Infection

A US and UK joint study suggests that drinking green tea may have a role in preventing HIV infection [4]. The preliminary study is published in the Journal of Allergy and Clinical Immunology and was a joint project between the University of Sheffield, UK, and Baylor College of Medicine, in Texas, USA.The research team did test tube experiments on a green tea flavonoid called epigallocatechin gallate (EGCG) and showed that it binds with CD4 immune system T-cell receptors and stops HIV from doing the same. One of the researchers, Professor Mike Williamson of the Department of Molecular Biology and Biotechnology at the University of Sheffield said, “Our research shows that drinking green tea could reduce the risk of becoming infected by HIV, and could also slow down the spread of HIV.” Before people jump to conclusions that this study suggests green tea could deny HIV a foothold in the immune system, critics are cautious and say it is very early days. Compounds that show good results at the “micro” level of cells in a test tube do not necessarily have the same effect at the “macro” level of immune systems in living organisms.Prof Williamson was keen to point out that green tea is not a cure, and neither is it a safe way to avoid infection. The study merely suggests that EGCG “has potential use as adjunctive therapy in HIV-1 infection,” he said, “it should be used in combination with conventional medicines to improve quality of life for those infected”.

Preventing Prostate Cancer

After a year’s oral administration of green tea catechins (GTCs), only one man in a group of 32 at high risk for prostate cancer developed the disease, compared to nine out of 30 in a control, according to a team of Italian researchers from the University of Parma and University of Modena and Reggio Emilia led by Saverio Bettuzzi, Ph.D. [5]“Numerous earlier studies, including ours, have demonstrated that green tea catechins, or pure EGCG (a major component of GTCs), inhibited cancer cell growth in laboratory models,” Bettuzzi explained. “We wanted to conduct a clinical trial to find out whether catechins could prevent cancer in men. The answer clearly is yes.” Earlier research demonstrated primarily that green tea catechins were safe for use in humans. Bettuzzi and his colleagues had found that EGCG targets prostate cancer cells specifically for death, without damaging the benign controls. They identified Clusterin, the most important gene involved in apoptosis, or programmed cell death in the prostate, as a possible mediator of catechins action. “EGCG induced death in cancer cells, not normal cells, inducing Clusterin expression” said Bettuzzi. To gauge susceptibility for prostate cancer among their research subjects, the team of Italian scientists recruited men with high-grade prostatic intraepithelial neoplasia - premalignant lesions that presage invasive prostate cancer within one year in nearly a third of cases and for which no treatment was given. Eligible men were between 45 and 75 years of age. Vegetarians and men consuming green tea or derived products, or those taking anti-oxidants or following anti-androgenic therapy were excluded. Of the 62 volunteers, 32 received three tablets per day of 200 mg each GTCs; the remainder were given a placebo. Follow-up biopsies were administered after six months and again at one year. Only one case of prostate cancer was diagnosed among those receiving 600 mg daily of GTCs, while nine cases were found in the untreated group. The 30 percent incidence rate among controls is consistent with previous findings, as was the absence of significant side effects or adverse reactions.

Protecting Brain Cells

Green tea can apparently inhibit the formation of the lethal protein aggregates that are a characteristic feature of Huntington’s disease (HD). This finding was reported by Dagmar E. Ehrnhoefer, a member of the research group of Dr. Erich Wanker of the Max Delnmter for Molecular Medicine Berlin-Buch (MDC) Germany, at the international conference “Neurodegenerative Diseases: Molecular Mechanisms in a Functional Genomics Framework” in Berlin [6]. She was able to show in an in vitro experiment that the substance epigallocatechin-3-gallate (EGCG), extracted from green tea, interferes with very early events in the aggregation process of the mutant huntingtin protein. Cytoxicity is also reduced. Huntington’s disease, along with Alzheimer’s and Parkinson’s, belong to the family of neurodegenerative diseases caused by protein misfolding.

Inhibiting Urinary Stone Formation

Researchers from the Department of Urology, Seoul National University College of Medicine and Clinical Research Institute, Seoul National University Hospital, Seoul, Korea sought to evaluate in a study whether epigallocatechin gallate (EGCG) could protect against cellular toxicity by oxalate and whether green tea supplementation attenuates the development of nephrolithiasis in an animal model [7]. Cells of the NRK-52E line were incubated with different concentrations of oxalate with and without EGCG, and toxicity and malondialdehyde assays were done to investigate the cytotoxic effect of oxalate and the anti-oxalate effect of EGCG. In a second series of experiments, male Sprague-Dawley rats were divided into three groups. Group 1 animals (controls) were fed regular chow and drank water ad libitum; group 2 animals were fed chow containing 3% sodium oxalate with the administration of gentamicin (40 mg/kg) and drank water ad libitum; group 3 animals were fed the same diet as group 2 with gentamicin administration and drank only green tea. Rats were killed 4 weeks later after a 24-hour urine collection, and the kidneys were removed for morphologic examination. As oxalate concentrations increased, the number of surviving cells decreased, and the formation of free radicals increased. The administration of EGCG inhibited free-radical production induced by oxalate. Green tea supplementation decreased the excretion of urinary oxalate and the activities of urinary gammaglutamyltranspeptidase and N-acetylglucosaminidase. The number of crystals within kidneys in group 3 was significantly lower than in group 2. Green tea has proven to have an inhibitory effect on urinary stone formation, and the antioxidative action of EGCG is considered to be involved.

References:

[1] H Gradisar, P Pristovsek, A Plaper, and R Jerala – “Green Tea Catechins Inhibit Bacterial DNA Gyrase by Interaction with Its ATP Binding Site” - Journal of Medicinal Chemistry 50 (2), 264 -271, 2007. 10.1021/jm060817o S0022-2623(06)00817-X

[2] S Kuriyama, T Shimazu, K Ohmori, N Kikuchi, N Nakaya, Y Nishino, Y Tsubono, and I Tsuji – “Green Tea Consumption and Mortality Due to Cardiovascular Disease, Cancer, and All Causes in Japan” - JAMA. 2006;296:1255-1265.

[3] S Ahmed, A Pakozdi, A E Koch, and W D Robinson - Study presented April 29 at the Experimental Biology 2007 in Washington, D.C. – Source: University of Michigan Health System, www.med.umich.edu

[4] M P Williamson, T G McCormick, C L Nance, W T Shearer – “Epigallocatechin gallate, the main polyphenol in green tea, binds to the T-cell receptor, CD4: Potential for HIV-1 therapy.” - The Journal of Allergy and Clinical Immunology, December 2006 (Vol. 118, Issue 6, Pages 1369-1374).

[5] Saverio Bettuzzi et al. – Study presented at the 96th Annual Meeting of the American Association for Cancer Research.

[6] D E Ehrnhoefer, M Duennwald, P Markovic, J L Wacker, S Engemann, M Roark, J Legleiter, J L Marsh, L M Thompson, S Lindquist, P J Muchowski, and E E Wanker – “Green tea’s epigallocatechin-gallate modulates early events in huntingtin misfolding and reduces toxicity in Huntington’s disease models” - Human Molecular Genetics, 15 September 2006; 15: 2743 - 2751.

[7] B C Jeong, B S Kim, J I Kim, H H Kim – “Effects of green tea on urinary stone formation: an in vivo and in vitro study” – Journal of endourology 2006 May;20(5):356-61. 

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