Drinking black tea may reverse a process called endothelial dysfunction that occurs in patients with coronary artery disease (CAD). Both short- term and long-term effects of tea drinking were found for CAD patients according to a study at the Boston University School of Medicine in Massachusetts.
The endothelium is a thin membrane that lines the inside of body cavities, including the heart and blood vessels. Dysfunction with the endothelium can lead to the constriction of blood vessels and the buildup of plaque within the arteries. Endothelial dysfunction is a known result of coronary artery disease.
Black tea contains antioxidants called flavonoids. Antioxidants are substances that prevent or slow oxidation by protecting body cells from being damaged by oxygen free radicals. Oxygen free radicals are substance in the body that are either created as byproducts of metabolism or enter the body through pollutants such as air pollution or tobacco smoke.
The oxygen free radicals create a chemical change (oxidation) in LDL cholesterol, which the body then tries to fight with white blood cells. When white blood cells encounter oxidized cholesterol, a fatty plaque is created that damages the walls of the arteries. This process is called calcification.
Previous research had identified a link between the regular drinking of black tea and a decreased risk of coronary artery disease. Researchers where unable to determine whether it was the flavonoids in tea that caused this benefit, or other substances such as water or caffeine.
For the study, researchers took 66 patients with coronary artery disease and had them drink either black tea or water. Researchers than measured both short-term effects (2 hours after drinking about 15 oz.) and long-term effects (4 weeks of drinking about 30 oz. daily) of drinking both the black tea and the water. An ultrasound test was used to measure the effects.
The results were that drinking tea produced both short-term and long-term improvements in endothelial function, whereas drinking water produced no improvements. In addition, researchers had some participants take caffeine pills with doses similar to those found within the tea. The caffeine pills produced no significant changes in endothelial function.
Researchers concluded that drinking black tea produced both short-term and long-term benefits for patients with coronary artery disease. The role of antioxidants in this process needs to be explored further.