Last year, 47,000 people ran in the New York City marathon — and there were more than 600 other marathons held in other cities across the country. Triathlons, ultra-marathons and other types of extreme endurance events are becoming increasingly popular as people test their limits and push themselves in the name of good health.


But is extreme exercise actually healthy? Is running 26.2 miles better for you than running a more-reasonable distance?


According to new research, no. As reported in the journal Mayo Clinic Proceedings, lead researcher Dr. James O’Keefe, a cardiologist at the Mid America Heart Institute of St. Luke’s Hospital in Kansas City, found that physical activity, like so many things in life, is best practiced in moderation.


“As great as exercise is, it’s like a powerful drug,” he says. “More is better up to a certain dose, but after that there is a point of diminishing returns, and it may actually detract from [heart] health and even your longevity.”


The research team poured over studies of people who trained and participated in endurance events such as marathons, triathlons, ultra marathons and long bike races. They found that people who exercised on a regular basis benefited significantly and increased their lifespan by an average of seven years over those who didn’t exercise. But when O’Keefe and colleagues looked at extreme athletes, they discovered that the healthful effects of their exercise not only decreased, but actually turned against them.


According to Time magazine, the problem is increased levels of the enzyme troponin. The enzyme is released when the heart muscle is in distress, and during extreme exercise it can climb as heart muscle fibers start to tear under the pressure of constantly pumping at a high level.


The damage doesn’t happen overnight, but over time scar tissue forms on the heart, and endurance athletes end up having thicker right atria and larger right ventricles. A thickened and scarred heart is more susceptible to abnormal heart rhythms, says O’Keefe. Studies have shown that endurance athletes have a five times higher risk of atrial fibrillation, or fluctuations in the heartbeat that can create greater cardiac risk.


One of the co-authors of the new data, Dr. Carl Lavie, medical director of cardiac rehabilitation and prevention at the John Ochsner Heart and Vascular Institute in New Orleans, noted that the best amount of running for increased longevity is about 10 to 15 miles per week. “We were thinking that we would see progressively more benefit the more you ran,” Lavie said. “We thought it would level off at some point. But not only did the runners not get more benefit, but the more they did, the faster they ran, the more frequently they ran, the more miles they ran, they actually seemed to lose any benefit to the heart.”


Says O’Keefe, “What we need are more people doing moderate exercise daily, and not running heroic distances. You can get 70 percent to 80 percent of the benefit of exercise from doing it 15 to 30 minutes a day.”


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