A new study shows a potential link between extreme endurance exercise and increased risk of advanced colon cancer in younger adults, according to research at Inova Schar Cancer Institute, in Fairfax, Virginia.
Dr. Tim Cannon, a medical oncologist, told WTOP after examining several young endurance runners under the age of 40 who had advanced colon cancer, he hypothesized that prolonged stress on the gut during long-distance running may trigger cancer-causing mutations.
In the study of 100 adults between the ages of 35 and 50, who had run five or more marathons or two or more ultramarathons, Cannon found 15% of the participants had advanced adenomas, which are precancerous lesions, compared to the expected 1% to 2% in non-runners in this age range.
In addition, 41% had at least one adenoma.
“The normal risk in the 35 to 50 population would be one-fifth of those numbers,” Cannon said.
The average age of the participants was 42.5 year old — two and half years before the recommended age of 45, for a first screening colonoscopy.
“The reason we all get colonoscopies, or we should all get colonoscopies, when we turn 45, is because if we remove a polyp or adenoma before it becomes cancerous, then we’re likely going to be safe from cancer,” Cannon said.
An often-ignored warning sign for endurance athletes
Cannon said long distance runners, and many of their physicians, have downplayed bleeding after a run.
“It’s very common among long distance runners, and it’s often been called ‘runner’s colitis,'” Cannon said. “The slang is ‘runners’ trots.'”
“People have assumed that ‘runner’s colitis’ is a benign entity, so they’ve been saying ‘It’s normal for runners to bleed.’ And the reason I know this, is because that’s what these runners who have cancer are telling me,” Cannon said.
Cannon said blood in the stool, for runners or any person, should be checked out.
“The most common presenting symptom for someone with colon cancer is blood in their stool,” Cannon said. “That’s the most common reason we learn someone has polyps or cancer is because they’re bleeding.”
Cannon said further research is underway, in examining this possible link. However, there could be other reasons extreme endurance athletes seem at risk of developing colon cancer at younger age.
“It could be the runners’ diets. It could be other aspects of their lifestyle that they have in common. It could be they drink from bottles with BPA or some other carcinogen more often than regular people,” who don’t engage in similar long-distance activities.
However, Cannon hopes that this preliminary study will prompt runners to get screening colonoscopies before the age of 45.
“I do think that it should raise awareness that any bleeding from a runner is a reason get a colonoscopy, and not something to be ignored,” Cannon said. “Exercise is good, overall — please don’t use this as an excuse not to exercise.”
