~ 070408 Green Tea Improves Endothelial Function

The June, 2008 issue of the European Journal of Cardiovascular Prevention and Rehabilitation published the results of a trial led by Dr Nikolaos Alexopoulos and colleagues at the Athens Medical School in Greece which found that drinking green tea improved endothelial function in men and women. Dysfunction of the endothelial cells which line the circulatory system is a critical event in the development of atherosclerosis, which leads to heart attack and stroke.

The current study tested the effects of three substances: 6 grams of green tea brewed in 450 milliliters boiled water, 125 milligrams caffeine, and hot water as a placebo, in 14 healthy participants with an average age of 30 years. Half of the subjects were smokers. Flow mediated dilatation of the brachial artery, which evaluates endothelial function by measuring artery diameter after a brief period of restricted blood flow, was assessed before the intake of each substance, and at 30, 90 and 120 minutes (time points when the peak plasma concentration of caffeine and tea flavonoids occur), for each of the three sessions.

While caffeine and hot water failed to demonstrate significant effects, there was a peak increase of 3.9 percent in endothelium-dependent brachial artery dilatation 30 minutes after the subjects consumed green tea. The finding supports the associated observed between green tea drinking and decreased cardiovascular disease risk. Tea flavonoids have antioxidant effects which may be responsible for their benefits; however green tea’s flavonoids may be more potent than those of black tea because the leaves have not undergone oxidation.

"These findings have important clinical implications," stated study coauthor Dr Charalambos Vlachopoulos. "Tea consumption has been associated with reduced cardiovascular morbidity and mortality in several studies. Green tea is consumed less in the Western world than black tea, but it could be more beneficial because of the way it seems to improve endothelial function. In this same context, recent studies have also shown potent anticarcinogenic effects of green tea, attributed to its antioxidant properties."

"Green tea consumption has an acute beneficial effect on endothelial function, assessed with flow-mediated dilatation of the brachial artery, in healthy individuals," the authors conclude. "This may be involved in the beneficial effect of tea on cardiovascular risk."

Related Health Concern: Stroke and cerebrovascular disease

Researchers have conducted thousands of clinical trials searching for better ways to prevent and treat stroke victims. As a result, we have a robust knowledge of cerebrovascular disease, and we are learning more every day. As with atherosclerosis in the coronary arteries (coronary artery disease), the underlying cause of ischemic stroke can often be traced back decades, to early insults to the inner lining (endothelium) of the arteries that set a deadly chain reaction into motion.

Now that they have identified endothelial dysfunction as a fundamental process of cardiovascular and cerebrovascular disease, along with the prime risk factors for endothelial dysfunction, such as high blood pressure and smoking, researchers are pursuing new therapies aimed at stroke prevention by improving the health of our arteries.

Stroke is primarily a condition of the elderly, mostly because of the cumulative effects of endothelial dysfunction, which can take decades to reach a crisis point. Nearly three quarters of all strokes occur in people who are over the age of 65, and the risk of stroke more than doubles every decade beyond the age of 55 (NINDS 2005).

Arteries are composed of three layers. The outer layer is mostly connective tissue and provides structure to the layers beneath. The middle layer is smooth muscle and contracts and dilates to help blood flow and maintain blood pressure. And the inner layer is a thin layer of endothelial cells and provides a smooth, protective surface. Endothelial cells prevent toxic, blood-borne substances from penetrating the smooth muscle of the artery. They also respond to changes in blood pressure and release substances into the cells of the smooth muscle that help change the tone of the artery.

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