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Study Shows Tea Consumption Lowers Blood Cholesterol
By Rosalie Marion Bliss
September 30, 2003
Drinking tea lowered low-density lipoprotein, the LDL "bad" cholesterol, in a small group of volunteers in an Agricultural Research Service study reported in the October issue of the Journal of Nutrition. The study was led by research chemist Joseph T. Judd with the agency's Diet and Human Performance Laboratory, one of seven laboratories at ARS' Beltsville Human Nutrition Research Center. ARS is the U.S. Department of Agriculture's chief scientific research agency.
"These findings illustrate the impact of specific types of health-promoting phytonutrients on the diet," said Ed Knipling, Acting Administrator for ARS.
Judd's study assessed the effects of black tea consumption on blood lipid concentrations in adults with mildly high cholesterol. Seven men and eight women were given five servings of black tea per day for three weeks, and a tea-flavored water for another three-week period. In a third study period, caffeine was added to the tea-flavored water in an amount similar to that found in the tea.
"Overall, we found a 6 to 10 percent reduction in blood lipids in black tea drinkers in just three weeks," said Judd. The study showed no effect on high-density lipoprotein, the HDL "good" cholesterol. The study's authors concluded that drinking black tea, in combination with following a prudent diet moderately low in fat, cholesterol and saturated fatty acids, reduces total and LDL cholesterol by significant amounts and may reduce the risk of coronary heart disease.
While several previous studies based on population surveys revealed a link between green and black tea consumption and reduced risk of coronary heart disease, experimental clinical studies failed to confirm effects of tea consumption on risk factors for coronary heart disease. According to Judd, many of those studies may not have adequately controlled the background diets of the volunteers. "Other foods or nutrients consumed during the studies could have affected the risk factors," he said.
The Camellia sinensis plant is the source of three major classes of teas known as green, black and oolong. Unlike herbal teas, these teas contain caffeine, unless decaffeinated. About 90 percent of tea consumed in the United States is black. Green tea contains more simple antioxidant flavonoids, while black tea contains more complex varieties.
Judd's study appears in the October Journal of Nutrition among other proceedings from the Third International Scientific Symposium on Tea and Human Health held at USDA last year in Washington, D.C. Research on the effects of antioxidant phytonutrients in tea on coronary heart disease risk is ongoing at the Beltsville Human Nutrition Research Center.