Findings Published in October Issue of Journal of Nutrition
NEW YORK, Sept. 30 -- Consuming 30-32oz of tea daily over a period of time -- the fluid equivalent of 2.5 cans of soda -- may reduce Low Density Lipoprotein (LDL, or "bad") cholesterol levels by more than 10 percent and decrease the risk of DNA damage caused by smoking, according to new research published as a supplement in the October 2003 issue of the Journal of Nutrition. These and other studies, including government research utilizing emerging biomarkers of cardiovascular health, are included in the supplement titled Proceedings of the Third International Scientific Symposium on Tea and Human Health: Role of Flavonoids in the Diet and provide further evidence of tea's disease-fighting potential in the areas of cardiovascular health and cancer.
"This collection of research calls attention, once again, to the potential for tea and possibly other flavonoid-rich beverages to contribute to healthful dietary patterns in a significant way," said Journal of Nutrition Supplement guest editor, Jeffrey Blumberg, PhD, Professor, Friedman School of Nutrition Science and Policy and Chief, Antioxidants Research Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston. "These studies further add to our understanding of the role that tea may play in protection against cardiovascular disease and certain cancers, including cancer caused by oxidative damage resulting from cigarette smoking. As scientific discoveries in this area continue, we hope to see new dietary recommendations reflect data about phytochemicals, including the flavonoids that are found in high concentration in tea."
Black Tea Consumption Improves Indicators of Heart Health
Results of a newly published clinical trial showed that five servings of black tea per day reduced LDL ("bad") cholesterol by 11.1 percent and total cholesterol (TC) by 6.5 percent in mildly hypercholesterolemic adult study participants. The study is the first of its kind to examine the effect of black tea on blood lipids while all other components of the diet were kept constant. By providing the volunteers with a strictly controlled diet during the study, the investigators were able to eliminate potentially confounding dietary factors.
Researchers at the United States Department of Agriculture (USDA) Beltsville Human Nutrition Research Center in Beltsville, MD, studied the effect of five six-ounce servings per day of either black tea, a caffeine-free placebo or caffeinated placebo beverage in 15 mildly hypercholesterolemic adults for three weeks. The volunteers followed a "Step I" type diet, moderately low in fat and cholesterol, as described by the American Heart Association and the National Cholesterol Education Program during the trial. After three weeks, the researchers examined participants' lipid profiles, including total cholesterol, LDL cholesterol, as well as two emerging biomarkers for cardiovascular health which some scientists argue could provide more in-depth measures of individual cardiovascular disease risk than LDL and TC alone: Apolipoprotein B (ApoB) and Lipoprotein(a) [Lp(a)].
Levels of ApoB decreased by 5 percent and levels of Lp(a) fell by 16.4 percent. ApoB concentrations reflect the number of LDL "particles" in the arteries, providing a more specific measure of LDL cholesterol levels. Lp(a) are lipoprotein particles that contain a particular protein which could potentially interfere with the body's ability to dissolve blood clots. Some scientists believe that a reduction in Lp(a) levels suggests a benefit to cardiovascular health. This reduction in Lp(a) could be important because most standard cholesterol treatments have little effect on this lipoprotein. This is an emerging biomarker which may become an important risk factor not reflected in LDL or TC measures, because of the role blood clots play in the risk of stroke and myocardial infarction.
One possible mechanism for this effect is tea's potential ability to limit cholesterol absorption in the intestines.
"These study results indicate that drinking tea regularly has the potential to lower levels of LDL cholesterol, reducing risk factors of cardiovascular disease," said Joseph Judd, PhD, Research Chemist, Beltsville Human Nutrition Research Center, USDA.
Green Tea Reduces Oxidative Damage that Could Lead to Cancer
Led by Arizona College of Public Health, University of Arizona and Arizona Cancer Center in Tucson, Arizona, researchers studied the effect on 143 heavy smokers of consuming four eight-ounce servings per day of either decaffeinated green tea, decaffeinated black tea or water for four months. The results showed that the levels of 8-OHdG, an indicator of oxidative DNA damage, dropped by a significant 31 percent after four months in those in the green tea group, but not in the other two groups. Oxidative DNA damage is implicated as a contributor to cancer development as well as cardiovascular disease.
"Tea polyphenols are not only powerful antioxidants but also inducers of phase-2 detoxification enzymes, resulting in the body's ability to quench more oxidative DNA damage, reducing cancer risk," said Iman A. Hakim, MD, PhD, MPH, Division Director, Health Promotional Sciences, Arizona Cancer Center and Research Associate Professor of Public Health, College of Public Health, University of Arizona.
Smokers were selected as participants due to the high levels of oxidative DNA damage cigarette smoking causes, making changes in those levels easy to detect. Researchers believe that the process of decaffeination affects black tea much more than green tea, thus the black tea may have been weakened because many of the flavonoids had been removed.
Growing Body of Evidence
The Proceedings of the Third International Scientific Symposium on Tea and Human Health: Role of Flavonoids in the Diet provides the latest scientific update from key researchers from Europe and the United States on their clinical and epidemiological studies in the areas of cardiovascular health and cancer. The ongoing scientific exploration of the health benefits of drinking tea has led to a growing body of research that points to tea as an important contributor to overall health. This extends the base of credible, published data supporting the health benefits of tea, encouraging the scientific community to continue exploring this exciting area.
Since tea is the second most consumed beverage in the world, tea's potential health benefits could have important implications on human health and disease prevention. To this end, researchers plan to probe deeper into the various mechanisms by which tea flavonoids function in the body and their implications. Clinical trials now underway and being planned will provide further important information about the role of tea in health promotion.