Latest reseach on tea and health
Washington, DC, September 15 - Leading scientists from around the globe gathered yesterday in Washington, DC for the Second International Scientific Symposium on Tea & Human Health to review the latest findings on the health benefits of tea, including the first study to show direct evidence of tea’s protective effects against a pre-cancerous condition in humans.
Major research developments since the first Symposium in 1991 include new data that suggest:
· Tea may have protective effects against several types of cancer - oral, digestive, lung and colorectal - in human and animal studies.
· Tea has greater antioxidant power than many fruits and vegetables
· Tea consumption may reduce risk of heart disease and stroke
· Black tea, the most widely consumed, has a wide range of health benefits
The symposium was sponsored by the American Health Foundation, the American Cancer Society, the Nutrition Committee of the American Heart Association, and the Tea Council of the USA and was held at the U.S. Department of Agriculture. At the meeting, leading researchers from Japan, China, England and The Netherlands joined American scientists in presenting the latest clinical, laboratory and epidemiological data on the role of tea in disease prevention.
"Tea, which is the second most consumed beverage in the world next to water, has great potential to help reduce the incidence of major diseases world-wide, especially when combined with a healthy lifestyle," said John Weisburger, Ph.D., M.D. (hc), Symposium chairman and Senior Member of the American Health Foundation. "In the pst eight years, we have made tremendous strides in understanding the potential of both black and green tea to prevent chronic illness, which has important implications for public health."
Studies Suggest That Tea May Have Protective Effects Against Several Types Of Cancer
Oral Cancer: A never-before presented study conducted by Junshi Chen, M.D. of the Chinese Academy of Preventive Medicine in Beijing, is the first to show direct evidence of the protective effects of tea on human cancer. Dr. Chen studied 59 patients with diagnosed pre-cancerous oral lesions over six months and found that treatment with a mixture of green and black tea components - consumed orally and applied topically - significantly improved the clinical signs and inhibited the proliferation of the pre-cancerous cells. "The results indicate that tea treatment may delay the progression of pre-cancerous lesions into oral cancer," said Dr. Chen. "This is the first time we have seen tea play a major role in protecting against the formation of cancer in humans."
Lung Cancer: Highlights of other studies presented on the chemopreventive effects of tea included research by Fung-Lung Chung, Ph.D., American Health Foundation, who looked at the effect of black tea on the development of lung tumors in mice and rats. He found that both green and black tea consumption retarded the development of the lung cancer, which was induced by carcinogens found in tobacco. In a related study on humans conducted by J.E. Klaunig, Ph.D., Dept. of Pharmacology and Toxicology, Indiana University School of Medicine, consumption of black and green tea reduced the level of oxidative stress, especially in smokers. According to Dr. Klaunig, "The results are very promising and suggest that over the long-term, tea may be able to reduce human diseases caused by increased oxidative stress, especially in smokers."
Colon Cancer: New research on colon cancer, the second leading cause of cancer-related death in the U.S., was also reported. In studies conducted by Roderick H. Dashwood, Ph.D., Linus Pauling Institute, Oregon State University, consumption of black and green tea inhibited the formation and development of very early, re-cancerous lesions in the colons of rats.
Digestive Cancers: In separate presentations, two researchers from the National Cancer Institute discussed data that appear to link tea consumption to decreased risk of digestive tract and other cancers, and preclinical studies suggesting the protective effects of green and black tea on pre-cancerous cells. A number of new studies focusing on the chemopreventive mechanisms of tea compounds in the body were also reviewed.
The Antioxidant Power of Tea
Tea is a naturally rich source of plant compounds known as flavonoids, which function as antioxidants to neutralize free radicals that can damage the body’s cells and lead to disease. Two major studies presented at the Symposium indicated that the antioxidants in tea are more potent than those found in many fruits and vegetables.
Research by Ron Prior, Ph.D., USDA Human Nutrition Research Center on Aging at Tufts University, and Guohua Cao, M.D., Ph.D. from the University of Connecticut at Storrs, measured antioxidant activity in dry tea found that tea exerts more potent antioxidant activity than 22 fruits and vegetables.
Catherine Rice-Evans, Ph.D., Antioxidant Research Centre, Guy’s King’s and St. Thomas’s Schools of Medicine and dentistry at King’s College in London, also found that catachins and flavonols, the most significant antioxidants in tea, had a greater ability to counter oxidative damages caused by reactive oxygen and nitrogen species than antioxidants from many fruits and vegetables.
In addition, when Dr. Prior’s team placed a black tea bag in a cup of boiling water, 85% of the total antioxidant activity was solubilized within the first five minutes of brewing. "This means that the antioxidants moved quickly into the water, suggesting that drinking one cup of tea could make a significant contribution to daily antioxidant capacity intake, equivalent to approximately one serving of vegetables," said Dr. Prior. However, Dr. Prior indicated that antioxidant capacity intakes equivalent to 4-5 servings of fruit and vegetables may be needed to impact total antioxidant capacity in blood and other tissues.
"Bioavailability of Tea Flovonoids" by Lillian Tijburg, Ph.D., Unilever Research, The Netherlands, showed that consumption of a single dose of tea increases total antioxidant activity in the blood, and that catechins in black and green tea are rapidly absorbed by the body.
"This research is significant because it tells us not only that tea has strong antioxidant capacity, but also how tea might work in the body," according to Beverly Clevidence, Acting National Program Leader for Human Nutrition, Agricultural Research Service, USDA. "Each step is key to ultimately understanding why an d how we should consume phytonutrient-rich foods."
Tea & Heart Disease - Some Promising Research
Tea flavonoids possess various properties that could potentially help reduce risk of heart disease, the most frequent cause of death in Western societies. Even a modest effect of tea on heart disease risk would be important for public health, according to Dr. Tijburg’s paper, "Tea Flavonoids and Cardiovascular Disease: A Review."
Some epidemiological studies have found that tea drinking is associated with a significant and substantial reduction in heart disease and stroke incidence. Tea flavonoids have been shown to lower LDL cholesterol levels in some animal models, and tea’s antioxidant activity has been shown to inhibit the oxidation of LDL cholesterol in vitro, but no consistent effect has been observed in human clinical studies. Dr. Tijburg suggests that further research is needed to clarify the effects in humans.
Black Tea - the Most Widely Consumed - May Have Health Benefits
At the time of the 1991 Symposium, nearly all of the research had been conducted on green tea. However, spurred by the fact that black tea is by far the most widely consumed world-wide (ninety-four percent of tea consumed in the U.S. is black), researchers at the 1998 Symposium presented the majority of research on black tea.** "The results overall show that black tea, because it is derived from the same plant as green tea, and has a similar chemical composition to that of green tea, possesses comparable antioxidant activity to green tea as well.
Gary Beecher, Ph.D., USDA Human Nutrition Research Center, Food Composition Laboratory, presented "Bioavailability and Metabolism of Tea Polyphenols: Analysis and Identification of Flavonoids." He explained that black tea has several unique types of flavonoids, that are well absorbed by the body and function as powerful antioxidants to ward off cell damage. According to Dr. Beecher, "one cup of black tea provides substantial amounts of compounds which have been shown to have protective effects against cancer and heart disease in the human and animal studies presented."
Future Study on the Health Benefits of Tea - What Lies Ahead
"It is my hope that the Second International Scientific Symposium on Tea & Human Health will encourage further study on the role of tea in disease prevention, through basic research in relevant models, and particularly through clinical research with human subjects," said Dr. Weisburger. "By focusing on how foods like tea can help prevent disease, we might not only save hundreds of thousands of lives, but also millions of dollars spent to treat illness."
Looking towards the future, researchers hope to find out more about how specific flavonoids in tea are used by the body and the mechanisms by which they may contribute to disease prevention in humans. Ultimately, long-term clinical research with humans will provide the answers.
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