The finding adds to a growing body of evidence that suggests that powerful antioxidants in green tea called flavonoids may protect the heart. Other flavonoid-rich foods include red grapes, red wine, and dark chocolate. The study authors say their results are the first to show that green tea offers a short-term improvement in the health of arteries. Black tea has previously been linked to short- and long-term improvements in endothelial function.

For the study, Nikolaos Alexopoulos and colleagues at the Athens Medical School in Greece randomly assigned 14 healthy volunteers approximately 30 years of age to a cup of green tea, a beverage containing the same amount of caffeine as green tea, or hot water on three separate occasions.

The researchers used a technique called flow-mediated dilation (FMD) to measure blood flow in each participant's arm at 30, 90, and 120 minutes after they drank their beverage. FMD is a noninvasive test that uses a blood pressure cuff and ultrasound to see how blood flows in the brachial artery when the arm is gently squeezed. The brachial artery runs from the shoulder to the elbow. The artery should get wider when blood flow in the area increases, but diseases such as atherosclerosis hamper this effect. FMD is an independent predictor of endothelial function and heart disease risk.

The key to the secret of green tea’s positive impact on heart disease and colorectal cancer may be the high levels of polyphenols (30 to 40 percent) found in green tea, compared with only 3 to 10 percent found in black tea. Polyphenols are chemical substances, found in plants, that have antioxidant properties. The four main polyphenols in tea leaves are epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC).

After drinking green tea, the subjects experienced significantly increased artery widening (dilation), with the highest increase noted at 30 minutes. The caffeinated beverage and hot water did not produce any significant changes in the same individuals.

Source: cbsnews.com