Green tea can increase arterial dilation, which is linked to better cardiovascular health. Researchers from Greece tested subjects after they consumed green tea, 125mg of caffeine and 450ml of hot water on three separate occasions.

They measured the diameter of the brachial artery in each participant 30, 90 and 120 minutes after they consumed each beverage. Arterial dilation increased significantly with tea by 3.69%, peaking at 30 min, whereas it did not change significantly with caffeine or water. (The acute effect of green tea consumption on endothelial function in healthy individuals. Eur J Cardiovasc Prev Rehabil. 2008 Jun;15(3):300-5).