Can Marathons Cause Blood Poisoning?

Four ways to avoid a potentially dangerous inflammatory response

Jun 17, 2015
Outside Magazine

A new study found that stress on ultramarathoners' bodies weakens the intestinal wall and allows endotoxins to leak into the bloodstream.    Photo: iStock


Researchers from Monash University in Australia recently uncovered an unsettling consequence of extreme endurance exercise: elevated levels of toxic gut bacteria. 

The stress of prolonged running on athletes' bodies—researchers looked at runners in 24-hour and multi-stage ultramarathons—weakens the intestinal wall and allows naturally present endotoxins to leak into the bloodstream, according to lead author Ricardo Costa. Any exercise that lasts longer than four hours can cause this, he says, especially if it's done multiple days in a row without giving the gut time to repair itself and return to normal. 

What's even scarier, though, is the body's response to leaky gut. The immune system recognizes invaders in the bloodstream, and releases inflammatory compounds to fight them—similar to how it would treat a serious infection like sepsis. This inflammatory response can cause fever, rapid heart rate, and serious complications, and can be even more dangerous than the bacteria themselves.

The good news? Costa's research has found that healthy, well-trained athletes’ bodies have higher levels of anti-inflammatory compounds, so they’re almost always able to neutralize the toxins, and the body's inflammatory response, before they cause real damage. Case in point: None of the athletes tested in his recent study experienced health problems, aside from unrelated GI stress, despite their elevated cytotoxin levels. 

If you're going long, follow Costa's advice to reduce inflammation 

Build Up Slowly and Progressively

"Those who take part with little or no specific training to cope with the distance and intensity are looking for trouble," says Costa. 

How slowly is slow enough? It's different for everyone, but Costa recommends staring several months out (or even a year, for ultra-distances), and using a coach or a training plan you trust. If you've done endurance events in the past, your muscle memory and cardio conditioning should serve some protection, but only if you've kept up your workouts. "The detraining effect occurs very quickly," says Costa. "You have to use it so you don't lose it."

Pay Attention to Race Conditions

If you'll be competing in hotter temperatures than you're used to, it will help to acclimate yourself beforehand if at all possible, and to have hydration and cooling strategies in place. (Overexertion in heat can also be a trigger of leaky gut, Costa's research found.) 

Train at Race Intensity

"In a race situation, an individual tends to push his or her body over its limits compared to training, so that may also induce greater gut perturbations," says Costa. "To avoid this, your training program should also occasionally push the body to its limits, allowing it to adapt to the exercise stimulus."

Don’t Short Recovery

Allow your body to recover thoroughly between training sessions, Costa says. This will allow time for your cells to adapt and build up a healthy immune response, and should protect you come race day.

As long as you're properly trained and don't push yourself much harder than you have on practice runs, don't worry about the potential effects of a leaky gut. Even if it happens, your body is prepared to repair it—just like it'll be prepared to run your best race. 

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