Each day, 150 million Americans drink 400 million cups of coffee. While some people can’t start their day without an extra-tall latte, others blame coffee for a whole range of symptoms, like jittery nerves, racing heart, and headaches. To determine whether there’s any basis to coffee’s negative reputation, researchers in Israel tested the effect of one of coffee’s best-known ingredients—caffeine—on the function of arteries. They gave caffeine pills to two groups of people—healthy subjects and ones with cardiovascular disease. Eighty-three percent of the people in the study were men. The pills contained 250 milligrams of caffeine—two-and-a-half times what is found in a cup of coffee. The researchers tested the endothelial function of the volunteers before and after taking the pill. Healthy subjects had better endothelial—or artery—function than those with heart disease, which is what the researchers expected. The endothelium is the innermost layer of the arteries that carry blood throughout your body. Good endothelial function is important for reducing the risk of cardiovascular diseases like heart attacks and stroke. High blood pressure, diabetes, and tobacco all mess with the function of the endothelium, which is why they are risk factors for heart disease. Exercise, on the other hand, can improve the endothelial function of your arteries. Researchers found that caffeine improved the artery function in both groups, but more so in the healthy subjects. They also saw small increases in the blood pressure of the people with heart disease, but none in the healthy subjects. Neither group, though, had an increase in heart rate or other negative symptoms. Coffee—or at least the caffeine—can actually have a positive impact on the arteries for some people. This is something to ponder next time you are waiting in line for a double-shot of caffeine.