Couch potatoes are no doubt celebrating the news, while runners recoil: Running can shorten your life, according to The Wall Street Journal. The newspaper says new research shows that over time, people who run more than 32 to 40 kilometres per week lose the longevity benefits of exercise as the activity wears on the heart.

"Running too fast, too far and for too many years may speed one's progress toward the finish line of life," the newspaper quotes an upcoming editorial in the British journal Heart, which highlights a second large-scale study that found people who run faster than 12 kilometres an hour won't increase their longevity, while slower runners gain significant mortality benefits.

"Chronic extreme exercise appears to cause excessive 'wear-and-tear' on the heart," it said.

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The findings may seem unbelievable, given all the research that shows how regular jogging prevents obesity, boosts bone density and improves cardiovascular health. Which is why some advocates of the exercise are scoffing at the editorial's claim.

"The guys advancing the hypothesis that you can get too much exercise are manipulating the data," ex-elite marathoner and sports cardiologist Paul Thompson told The Wall Street Journal. "They have an agenda."

In a column for Runner's World, The Globe and Mail's Jockology running expert Alex Hutchinson meticulously dissects the latest data, suggesting that the risks of premature death by running are exaggerated. (Check out his explanation here.) Hutchinson emphasizes he is not arguing that there is no diminishing returns for exercise, nor does he suggest there is no association between extreme running and heart damage.

"We can speculate all we want about 'potential' risks and benefits, but the real-world epidemiology is crystal-clear: If you exercise for an hour a day, you're likely to live longer than if you exercise less than an hour a day," he writes.

Earlier this year, Globe health reporter and columnist Andre Picard commented on a string of high-profile marathoner deaths, putting the risks into perspective: It's far worse for your health to be sedentary than to run marathons, he noted.

"Nobody is counting or cataloguing the La-Z-Boy deaths – the thousands of people who die while watching TV or another sedentary activity. The science is unequivocal: The sedentary – the 50 per cent plus of Canadians who barely move each day – are at greatest risk," Picard wrote.

As several avid runners on a Runner's World forum have pointed out, however, most don't run to increase their longevity anyway. There are many other compelling reasons to run. Namely, staying active is fun and it improves quality of life. "In addition to working out because I enjoy doing it, I think that it gives me more 'up time' while I'm alive. So far I take no medication; haven't needed back surgery, heart surgery, suffered from ED, depression or insomnia," one commenter wrote. "Even if I could get the same positive results with less time and effort, I'd still want to run enough to run marathons."

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Added another: "I don't run to improve my survival rate. I run because I enjoy it – I like being fit and I like challenging myself. If a study came out showing that running actually increased my likelihood of premature death, I'd still run."

Will this new research make you think twice next time you go for a long, fast run?