Are Marathons and Extreme Running Linked to Colon Cancer?

The three patients should have been portraits of health. They were young, lean and physically active. Unusually active, in fact: Two regularly ran 100-mile ultramarathons, and one had completed 13 half-marathons in a single year.

By the time they came to see Dr. Timothy Cannon, all three had advanced colon cancer. He was mystified; the oldest of them was 40, and none had any known risk factors. The doctor couldn’t help wondering if extreme running might have played a role.

So Dr. Cannon, an oncologist with Inova Schar Cancer in Fairfax, Va., launched a study, recruiting 100 marathon and ultramarathon runners aged 35 to 50 to undergo a colonoscopy.

The results were staggering. Almost half the participants had polyps, and 15 percent had advanced adenomas likely to become cancerous.

The rate of advanced adenomas was much higher than that seen among adults in their late 40s in the general population, which ranges from 4.5 percent to 6 percent, according to recent studies The figure among extreme runners was even higher than the 12 percent rate among Alaska Natives, who are unusually prone to colon cancer.

The research was presented at an American Society of Clinical Oncology conference but has not yet been published in a medical journal.