A small but important new study suggests that very intense long‑distance running may be linked to a higher risk of precancerous colon growths in some younger adults, especially marathon and ultramarathon runners.
What the study did
Researchers enrolled 100 runners between ages 35 and 50 who had completed at least five marathons or two ultramarathons and had never had a colonoscopy. People with hereditary cancer syndromes or inflammatory bowel disease were excluded so the team could focus on the possible impact of endurance running itself.
Each participant:
- Completed a survey about diet, bowel habits, and training history.
- Underwent a screening colonoscopy, with any polyps carefully reviewed by gastroenterologists, pathologists, and oncologists to see if they were advanced adenomas (higher‑risk, precancerous polyps).
Key findings for patients
The results were striking for this otherwise very healthy group of athletes:
- 15% had advanced adenomas, compared with about 1%–2% expected in average‑risk people of the same age.
- 41% had at least one adenoma (polyp).
- The average age was 42.5, younger than current guidelines that typically start routine colonoscopy at age 45 for average‑risk adults.
This early research does not prove that running causes colon cancer, and regular moderate physical activity is still known to lower colon cancer risk overall. However, it does suggest that extreme endurance training could be one additional risk factor for some people and that this group may benefit from earlier screening.
What this might mean for screening
These findings may help define a new group who should talk with their doctors about starting colon cancer screening sooner than current guidelines suggest. They are especially concerned about younger runners who notice blood in their stool after long runs, a symptom that has often been dismissed as “normal” but could be a sign that a colonoscopy is needed.
The good news is that screening can find and remove precancerous polyps before they turn into cancer, which can be life‑saving. Research is ongoing on how factors like diet, training patterns, and other lifestyle habits might influence risk in high‑endurance athletes, with the goal of improving early detection and prevention for this unique group.
Reference
Cannon TL, et al. Risk of pre-cancerous advanced adenomas of the colon in long distance runners. J Clin Onc. 2025;43:3619. Number 16_suppl
