Submitted to: Journal of Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2003
Publication Date: 10/1/2003
Citation: Davies, M.J., Judd, J.T., Baer, D.J., Clevidence, B.A., Paul, D.R., Edwards, A.J., Chen, S.C., Wiseman, S.A., Muesing, R.A. 2003. Black tea consumption reduces total and low density lipoprotein cholesterol in mildly hypercholesterolemic adults. Journal of Nutrition.
Interpretive Summary: Black tea is a major source of the flavonoid class of phytonutrients in Western diets. High intakes of these phytonutrients are thought to have very beneficial effects on health including reduced risk for cardiovascular disease. The mechanisms responsible of these effects on health remain under investigation. Two possible mechanisms were investigated in a controlled feeding study of black tea performed at the Beltsville Human Nutrition Research Center with 15 men and women. Tea phytonutrients are known to have antioxidant properties, which could reduce risk factors for cardiovascular disease. Most of these properties have been demonstrated on biological materials such as plasma, removed from the body for testing, i.e., ex vivo measurements. Measurement of a variety of parameters for oxidative stress and oxidative status failed to show any effect of black tea consumption on parameters that could be considered as in vivo indicators. However, tea consumption did lower blood concentrations of low density lipoprotein cholesterol by about 10%. This significant lowering of LDL, a major CVD risk factor, could account for all or part of the reduction in this disease seen in other studies. This was the first demonstration of cholesterol lowering effects of black tea in a controlled, clinical investigation. These results should be of interest to nutritionist, health professionals, and to the general public interested in defining a healthy diet especially as related to heart disease.
Technical Abstract: Background: Several epidemiological studies have found that green and black tea consumption are associated with reduced risk of coronary heart disease. Experimental studies designed to show that tea consumption affects in vivo markers of oxidative stress or blood cholesterol concentration, two major indicators of risk for CHD, have been mostly unsuccessful. However, in these studies the background diets were free-living diets, and were not carefully controlled for other foods or nutrients known to affect these risk factors. Objective: We assessed the effects of black tea consumption on blood lipid and lipoprotein concentrations in mildly hypercholesterolemic adults. The tea and other treatment beverages were included in a carefully controlled, weight-maintaining, prudent diet, moderately low in lipids, saturated fatty acids, and cholesterol. Design: Five servings per day of black tea were compared with a placebo beverage in a blinded, randomized crossover study where 7 men and 8 postmenopausal women consumed a controlled diet for 3 weeks per treatment at the Beltsville Human Nutrition Center's human studies facility. The placebo was prepared to match the tea in color and taste and contained no caffeine. In a third study period, caffeine was added to the placebo in an amount similar to that in the tea. Plasma lipids and lipoproteins were determined at the start and end of each study period. Plasma oxidized LDL, F2-isoprostanes, and urinary 8-hydroxy 2-deoxy d-guanosine were determined as indicators of oxidative stress. Plasma antioxidant status was estimated ex vivo by ferric ion reducing capacity, and by thiobarbituric acid reactive substances in the plasma LDL fraction which was isolated by ultracentrifugation. Results: Five servings per day of black tea reduced total cholesterol 6.5%, LDL cholesterol 11.1%, apolipoprotein B 5%, and lipoprotein(a) (Lp(a))16.4% compared to the placebo with added caffeine. Compared to the placebo without added caffeine, total cholesterol was reduced 3.8%, LDL cholesterol was reduced 7.5% while apolipoprotein B and Lp(a) were unchanged. HDL cholesterol, apolipoprotein A-I, and triglycerides were not affected by tea consumption. None of the markers of oxidative stress or oxidant status were affected by tea consumption compared to either placebo. Conclusion: The inclusion of black tea as part of a prudent diet moderately low in fat, cholesterol, and saturated fatty acids reduces total and LDL cholesterol by significant amounts and may, therefore, reduce the risk of CHD. Tea consumption had no effect on HDL cholesterol or apolipoprotein A-I. Tea consumption did not affect antioxidant status under the conditions of this study.