People looking to get fit use marathons as a goal to kickstart their exercise program, but a series of deaths during marathons has some wondering if they’re really so beneficial. Two runners in their 30s recently died during a half-marathon in California; and this weekend, three men aged 26, 36 and 65 died during the Detroit marathon (they were all competing in the half-marathon event). Still, the cause of death isn’t known for any of the runners and deaths during marathons are rare. A study presented at a conference of the American College of Cardiology, for instance, reported the risk of sudden death during a marathon is 0.8 per 100,000 people. The risk during a triathlon, which includes running, swimming and cycling, is 1.5 in 100,000. In childbirth, the risk of dying is 13 per 100,000 births, and the risk of dying in a car accident is 1 in 6,700. In a Canadian study, 129 non-elite runners received blood tests before running a full or half marathon. Prior to the run, their blood markers for heart injury were normal, but when they’d finished, most of the half-marathoners and more of the marathoners had elevated troponin and other markers of heart damage. After an hour, even more did. Even so, while several studies have found short-term heart damage among marathon runners, the benefits of regular exercise seem to outweigh the risks. “There’s no doubt the marathon is a very hard, stressful event,” says Dr. Paul Thompson, director of cardiology at Hartford Hospital. “We’re confident that exercisers have lower heart risks than non-exercisers, but the truth is we don’t know this for sure about marathoners.”