We know that long-distance running can be tough on your joints, but new research raises the question of whether it and other intense exercise done to extremes might harm your heart, too. While it was no surprise to researchers to see that a group of long-term regular marathon runners had less body fat and slower heart rates compared with a group of patients undergoing tests for heart disease, they had not expected to see that the runners had more plaque in their coronary arteries. And the more plaque, the greater your risk for heart attack -- not exactly what you would expect in elite athletes. For insight into this paradoxical effect, I sought out senior study author Robert S. Schwartz, MD, a cardiologist at the Minneapolis Heart Institute. We talked about the research and his theories about the results. Too Much of a Good Thing? The study compared 25 men (average age 60) who had run at least one marathon each year since 1985 with 23 sedentary patients of the same age who had suspected heart problems. Dr. Schwartz and his colleagues examined both groups and performed CT angiography on them to generate pictures of their blood vessels. On the plus side, investigators found that the marathoners had lower heart rates, blood pressure, weight and body fat than the non-athletes, along with higher levels of HDL (the "good" cholesterol). But they also had... Significantly more plaque in their coronary arteries. Higher calcium scores (reflecting calcium buildup in the cardiopulmonary vessels) and higher noncalcified plaque (deposits not yet hardened with calcium), although in this case the difference was not statistically significant. Since the runners had "healthy" cholesterol levels -- on average 190 mg/dL total cholesterol and 115 mg/dL LDL (the "bad" cholesterol) -- the researchers dont think diet explains the difference. One theory Dr. Schwartz told me about: Extreme exertion brings metabolic and mechanical stresses that keep the body in a constant state of inflammation that can cause plaque to form. Another theory is that arteries are strained because running raises heart rate and blood pressure. But, cautions Dr. Schwartz, these are strictly hypotheses -- no one knows the answers yet. Stay on the Run This study is in no way meant to discourage exercise, stresses Dr. Schwartz, who is an avid runner himself -- though perhaps it is smarter not to overdo it. Dr. Schwartz and his team are currently following these elite runners long-term, and they are now looking at female runners as well to see if the same results hold. They also plan to study moderate-distance runners to determine if there is a threshold of exercise at which extra plaque begins to develop. Well go the distance and be sure you stay up to date as the research continues. Source(s): Robert S. Schwartz, MD, cardiologist, Minneapolis Heart Institute, Minneapolis.