Drinking a cup of tea makes blood vessels work better within 2 hours, dilating the arteries and improving blood flow, according to Massachusetts researchers.

This may ultimately have a beneficial effect on the heart, according to Dr. Joseph A. Vita of Boston University. Tea’s beneficial effects on the heart have been known for years, but how it accomplishes this has been a mystery, Vita said at the annual meeting of the American Heart Association here.

In the study, Vita and colleagues had 50 men and women with known heart disease drink four cups of black tea a day for 4 weeks. They used a commercial brand, so that the amount of caffeine and other active ingredients was the same across the group. The participants also drank four glasses of water each day, and avoided other kinds of tea and red wine. The study participants were then monitored for another 4 weeks in which they drank water instead of tea.

Using ultrasound to measure blood flow in the forearm, the investigators found that the tea helped blood vessel function. While blood vessels normally dilate 11%, those with heart disease only dilated 6%. Tea drinking–but not water–restored blood vessel response to near- normal levels.

“The effects were visible as soon as (within) 2 hours of drinking the first cup, and the effects persisted after the 4 weeks,” Vita announced.

He said the effects were not due to the caffeine in the tea. The researchers had some of the participants swallow a caffeine tablet equivalent to 2 cups of tea and then repeated the artery response test. Caffeine had no response on the blood vessel function.

Antioxidants are known to improve blood vessel function, and black tea contains significant amounts of flavonoids, which are antioxidants, Vita noted. The researchers did find that flavonoid levels in the study participants’ blood increased with tea drinking.

“Thus, this study demonstrates that drinking tea reverses an important abnormality of blood vessel function in patients with coronary artery disease,” Vita reported. “However, further studies will be required before tea drinking can be recommended to patients as a way to protect against coronary artery disease and stroke.”

(Heartcenteronline.com, Nov 2000)