I like the metallic, blood-like taste in my mouth when my lungs scream for air. I welcome the numbing, rigor mortis of a 400-meter running race, when my body starts to feel like the walking dead look. That might sound strange. But I’m not alone.

Smithsonian.com reported that almost 2 million Americans hammered through a half-marathon in 2013. Hard core obstacle races, such as the Tough Mudder series, attract more masochists every year. According to Triathloncompetitor.com, “Between 2012 and 2013, the number of people who participated in at least one adventure race or road triathlon both increased by more than 25 percent.”

Exercise is good. But it’s like red wine. The Mayo clinic says that red wine can help our hearts, if it’s consumed in moderation. Research says the same about exercise. It’s good when the dose is right. After 31 years of thrashing my body, it’s time that I took notice.

When I’m resting, my heart beats about 40 times per minute. The American Heart Association says that most people’s hearts beat a heck of a lot faster. Low heart rates among athletes are considered signs of fitness.

At 45 years old, I can blitz through a mile in less than 5 minutes. But if you exercise lightly, 20 minutes a day, three times a week, your heart might be healthier.

Eight years ago, I failed a treadmill stress test during a medical exam. The word fail, of course, is relative. An EKG showed an unusual rhythm. Further tests weren’t conclusive, so I continued to run hard. The following year, I won Singapore’s JP Morgan Corporate Challenge against nearly 10,000 other runners.

But I wasn’t as fit as Laurent Vidal. He was a French, Olympic triathlete. He quit competing in 2014, after he had a heart attack while swimming. Two weeks ago, he died in his sleep. He was 31 years old.

We’ve all heard stories of athletes collapsing from heart failure. That’s how three of my friends died. One died during a 5 kilometer running race. The second dropped dead after he crossed a 10km finish line. The third had a heart attack while watching Oprah. He was relaxing after a triathlon training session. Each man was in his 50s.

In 2012, research cardiologist, James O’Keefe gave a TED talk that scared me stiff. Like me, he was an exercise junkie. But he has since found that moderate exercise, a few times a week, is better for longevity. “I’m in the business of finding out the ideal diet and lifestyle,” he says, “and I’m coming to the conclusion that running marathons and extreme endurance athletics do not fit into that recipe.”

Earlier this year, five researchers published a study in the Journal Of The American College of Cardiology. They found that, on average, joggers live about 6 years longer than couch potatoes. But those who run too far, too fast, or too frequently die earlier. They live about as long as a typical T.V. loafer.

The best survival rate came from those who ran 2 to 3 times per week, at an easy pace. Those who ran more than 2.5 hours per week died earlier. Those who ran faster than 7 miles per hour met the same fate.

Cardiologists Justin E. Trivax and Peter A. McCullough published Phidippides cardiomyopathy: a review and case illustration. They say endurance sports can hurt the heart. “It has been shown that approximately one-third of marathon runners experience dilation of the right atrium and ventricle, have elevations of cardiac troponin and natriuretic peptides, and in a smaller fraction later develop small patches of cardiac fibrosis that are the likely substrate for ventricular tachyarrhythmias and sudden death.”

Researchers from Rome’s Institute of Sports Medicine and Science published equally surprising findings in the European Journal of Preventative Cardiology. They studied 2,354 Olympic-level athletes between 2002 and 2014 to “assess the efficacy of the Olympic pre-participation screening protocol.” Tests determined how the athletes’ hearts performed under stress and whether there were any cardiovascular issues.

They concluded that, “Olympic athletes, regardless of their superior physical performance and astonishing achievements, showed an unexpected large prevalence of CV [cardiovascular] abnormalities, including life-threatening conditions.”

Cardiologist James O’Keefe, however, does give us hope. In his TED talk, he referenced a study on mice. One group ran hard on a treadmill over an 8 week period. Their resulting heart abnormalities were similar to those of humans who run too far, too frequently or too fast. But when researchers took the mice off their tough regimes, their heart muscles recovered.

I’m not a mouse. But I hope that works for me. I now run every second day. My runs are short, and my pace is easy. I’m no longer racing. But if I can live into my 80s, I’ll consider that a win.

Andrew Hallam is a Digital Nomad. He’s the author of the bestseller, Millionaire Teacher and The Global Expatriate's Guide to Investing: From Millionaire Teacher to Millionaire Expat.