Why it matters
A recent study is raising concerns in the endurance sports world, suggesting that extreme long-distance runners, including ultramarathoners and multi-marathon finishers, may face a higher risk of precancerous colon growths.
The findings, originally explained in a NY Times article, challenge long-held assumptions about the protective nature of high-volume exercise.
What’s happening
The study began after three young, physically fit endurance athletes, all under 40 and with no known risk factors, were diagnosed with advanced colon cancer. One was a triathlete, another had completed seven marathons in seven days, and a third regularly ran 100-mile ultramarathons. All three later died from the disease.
In response, oncologist Timothy Cannon at Inova Schar Cancer Institute launched a study focused on whether extreme exercise might be linked to colorectal cancer risk.
Presented at the American Society of Clinical Oncology (ASCO) conference this summer, the pilot study enrolled 100 runners between the ages of 35 and 50. Participants had either completed:
- Two or more ultramarathons (50K or longer), or
- At least five marathons (26.2 miles)
The results
- Nearly 50% had polyps
- 15% had advanced adenomas, precancerous growths with high potential to develop into cancer
These rates were significantly higher than expected. The general population in the same age range has an estimated 4.5% to 6% rate of advanced adenomas. Even Alaska Natives, one of the highest-risk groups, typically show a 12% rate.
Some participants underwent additional procedures following the discovery of multiple polyps. Many were surprised by the results, especially given that long-distance running is commonly associated with better overall health, including lower body mass, improved cardiovascular fitness, and reduced stress levels.
The bigger picture
The research is preliminary. It has not been peer-reviewed or published in a medical journal. The study also lacked a control group and did not fully capture family medical histories for all participants.
However, experts who reviewed the data say the results warrant further investigation. While there is no established link between endurance running and colorectal cancer, the data suggest a possible connection worth exploring.
Some physicians speculate that runners may overlook early warning signs, such as bloody stools, diarrhea, or bowel urgency, by attributing them to the physical demands of training. Endurance athletes may also experience ischemic colitis, a condition where reduced blood flow to the colon mimics similar symptoms.
Although ischemic colitis typically resolves on its own, there are questions about whether repeated inflammation could contribute to long-term cellular damage. As of now, there is no conclusive evidence linking ischemic colitis to colorectal cancer risk.
Despite the findings, researchers and physicians are not recommending a change in exercise habits. Instead, the emphasis is on vigilance. Runners, especially those over 35, are encouraged to monitor symptoms, speak with healthcare providers, and consider early screenings.
What runners should know
The U.S. Preventive Services Task Force lowered the recommended age for colorectal cancer screening from 50 to 45 in 2021 due to a national rise in early-onset cases. For high-mileage runners or those training at extreme intensities, earlier screenings may be beneficial.
While exercise remains broadly beneficial for health, this study highlights that high-performance athletes are not immune to serious illness. Listening to the body and reporting symptoms early, no matter how fit the individual appears, may be critical.
