Tea Lowers LDL Cholesterol and Cancer Risk
Solid evidence from two new placebo-controlled trials adds to a growing body of research that shows tea lowers LDL cholesterol levels and can prevent DNA damage. Damaged DNA is the first step in the development of cancer and is also associated with heart disease.
Tea may soon be added to the list of fruits and vegetables experts urge Americans to eat as often as possible to reduce their risk of disease, the researchers who produced these studies told a meeting sponsored by the US Department of Agriculture, the Tea Council, the American Cancer Society and other groups.
Tea contains a type of powerful phytochemical antioxidant called catechins. "It's taken about 30 years to fully appreciate the importance of these compounds," said Jeffrey Blumberg, a nutritionist at Tufts University in Boston, who acts as an adviser to both the US Food and Drug Administration and the Tea Council.
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The study to show tea's beneficial effects on cholesterol was conducted by Joseph Judd acting director of the USDA's Beltsville Human Nutrition Research Center, Maryland, and his colleagues. The subjects, 8 men and 8 women, agreed, for a period of 3 weeks at a time, to eat and drink only what they were given at the Beltsville lab. Their diet included 5 cups each day of either tea or a placebo-beverage flavored like tea. When tea-drinking subjects' blood lipids were measured, researchers found an up to 10% lowering of LDL, (low density lipoprotein, the "bad" cholesterol). Overall, the subjects' total cholesterol was an average of 6% lower during the 3 weeks they were drinking tea. And tea drinking only produced a drop in levels of LDL cholesterol, while leaving levels of beneficial HDL cholesterol constant.
The second study was led by Dr Iman Hakim at the University of Arizona and the Arizona Cancer Center. Dr. Iman Hakim tested 140 smokers to see if drinking tea would affect their levels of chemicals associated with DNA damage. This was evaluated by looking at a chemical marker of DNA damage in cells called 8-OHdG (8-hydroxy-2'-deoxyguanosine), which is excreted in urine. (Deoxyguanosine (dG) is a constituent of DNA and 8-OHdG is produced when free radicals oxidize dG).
Study subjects were asked to eat whatever they normally ate and to just add tea to their diet. For 4 months, these volunteers drank either green tea, black tea or water. Hakim's team tested their urine for levels of 8-OHdG.
"What we found was a 25% decrease (of 8-OHdG) in the green tea group," said Dr. Hakim. No changes were seen in the people who drank black tea or water. "We think green tea, in our group of smokers, is associated with a reduction of oxidative stress"" Hakim said.
Although more research is needed to see if lowering levels of 8-OHdG, or other markers of DNA damage, is actually associated with a lower risk of cancer, in the scientific community, many think tea can reduce the risk of cancer because it is loaded with phytochemicals. Phytochemicals provide a wide range of antioxidant molecules that counteract the damage done to DNA by free radicals, the electron-hungry molecules produced in the body by sunlight, chemicals, many foods and even the basic metabolic processes of living. When free radicals react with and steal an electron from DNA, the resulting damage to the cell's genetic template can impair normal cellular activity and possibly lead to cancer.
McKay DL, Blumberg JB. The role of tea in human health: an update. J Am Coll Nutr 2002 Feb;21(1):1-13. Fox, M. Tea may reduce risk of cancer, heart disease:Forum, Reuters Health, Sept. 25, 2002.