Read This: The Scary Reason Why Caffeine and Marathons Don’t Mix


Shutterstock contributor Jen A. Miller has a fascinating long read in e-magazine The Magazine this week. It’s all about the impact of higher-than-recommended doses of caffeine on endurance athletes—specifically, marathon runners—and how downing a lot of caffeine before and during a race can yield serious consequences for your heart health, including upping your chances for a heart attack.

Listen to this:

“The low-risk runner morphs into a high-risk runner in a race,” says Dr. Arthur J. Siegel, director of internal medicine at McLean Hospital and associate professor of medicine at Harvard Medical School. His studies on runners and cardiac arrest have appeared in the American Journal of Medicine and the World Journal of Cardiovascular Diseases.

These deaths can happen without caffeine, but caffeine makes any kind of underlying or temporary heart problem worse, Siegel says. That’s because caffeine affects myocardial blood flow, which is the rate at which blood moves through the heart’s muscles to infuse it with oxygen so it can push re-oxygenated blood out to the rest of the body.

…While [a combined 25o mg of] caffeine has no effect on myocardial blood flow when a body is at rest, it has a significant effect when you work out. Healthy bike riders experienced a 14 to 22 percent drop in myocardial blood flow; those with coronary artery disease experienced an 18 to 25 percent drop.

This is very bad news, because, when exercising, your arteries increase blood flow from 300 to 400 percent, says [10-time marathoner Dr. John P. Higgins, associate professor of medicine at the University of Texas Health Center in Houston]. Your heart needs to work harder, and therefore needs more blood flow to the myocardial muscles of the heart so it can keep the pumping going. But if your myocardial blood flow drops, you get what Higgins calls a “supply-demand mismatch.”

“You’re working your system more, and at the same time, you’re impairing your system’s ability to increase its blood flow,” he says. That starves the heart muscles of oxygen, which can lead to outcomes like chest pain, myocardial ischemia, or even myocardial infarction — a heart attack.

Scary, right? The piece is full of enough studies, anecdotes and expert input to get even the biggest skeptic thinking twice about his caffeine-and-running habits.

Take a few minutes and read it for yourself here.