Training to run a marathon has got to be one of the healthiest things you can do, right? Maybe not: A new study found that "moderate" runners lived longer than people who don't exercise at all—and people who run lots of miles, HealthDay reports. The study, led by the co-director of the Cardiovascular Research Institute at the Lehigh Valley Health Network, involved 3,800 runners who supplied info on their heart risk factors and their use of NSAIDs like ibuprofen; almost 70% of the group clocked more than 20 miles a week. The findings were presented Sunday, but have yet to be published in a peer-reviewed journal. According to the results, how much should you run? One cardiologist who reviewed the data suggests you do so no more than 2.5 hours per week, spread out between two or three sessions consisting of slow or moderately-paced running.
It's not clear why too much running might be bad for longevity, but the study appears to rule out factors like prior cardiac risk (linked to things like high blood pressure, high cholesterol, diabetes, family history, and smoking) or excessive use of NSAIDs (which have been linked to heart problems). One doctor who's also a running coach tells NBC San Diego that extreme exercise can actually "cause some scarring of the heart." And another recent study found that male marathon runners had more plaque in their coronary arteries—which can lead to a heart attack—than non-runners, Pioneer Press reports. Again, it's not clear why, but one researcher notes, "It is plausible, not proof by any stretch, that metabolic changes when running could be moderately toxic to arteries." (Another way to live longer: eat nuts?)