What’s the connection between caffeine, the finish line, and marathon deaths? An investigation of how much caffeine is too much for runners, and the explosion of caffeine-related products handed out at races:

Starting three years ago, the International Marathon Medical Directors Association (IMMDA) has warned runners to ingest no more than 200 mg of caffeine before and during a race, based on research that has shown that during exercise, caffeine affects the heart in ways that can send someone into cardiac arrest. “Every incident is disturbing,” says Dr. Lewis G. Maharam, chairman of the board of governors for the IMMDA and medical director of the Leukemia Lymphoma Society’s Team in Training. There was no single incident that led the group to put out the warning in 2010, but it stemmed from a “constant conversation on how to be safer.”

So far this year, four cardiac-related causalities have fit the pattern: Alain Rettig, 45, in the TCS Amsterdam Marathon, 1 km from the finish line; Ricki Savage, 27, in the Dublin Marathon at the finish line; Jake Zeman, 35, in the Rock ’n’ Roll Savannah Marathon, feet from the finish line; and Kyle Chase Johnson, 23, in the Pittsburgh Half Marathon, less than a mile from the finish line.