Long-distance runners can, in fact simply drop dead -- usually in the middle of a run, from fatal heart attacks. In 2010, three runners died at the 32nd Detroit Free Press/Flagstar Marathon.
In fact, about 14 percent of athlete deaths are linked to heart problems. Although exercise reduces your cardiovascular risk by a factor of three, too much vigorous exercise, such as marathon running, increases your cardiac risk by seven.
Healthier Talk reports:
“That’s because the further you run, the more stress you put on your body ... [L]ong duration exercise releases chemicals that flood your body. And that leads to inflammation ... If you have hidden heart problems, this can be seriously risky.”