Epidemiological studies consistently show that physically active people have a lower cancer incidence, including fewer colon polyps and lower rates of colorectal cancer. But what if there’s a paradox lurking at the extreme end of training?
A new prospective study (actually an abstract presented at a scientific conference — a key detail) suggests that high-volume marathon and ultramarathon running may actually increase the risk of advanced precancerous colon lesions.
Researchers enrolled 100 long-distance runners aged 35–50, all of whom had completed either at least two ultramarathons (≥50 km) or five marathons. Participants underwent screening colonoscopies, and a team of gastroenterologists, pathologists, and oncologists reviewed all polyps. The key outcome was the presence of “advanced adenomas”—polyps larger than 10 mm, with tubulovillous features, or showing high-grade dysplasia. In simple terms, polyps are more likely to turn into cancer. For comparison, the expected prevalence of advanced adenomas in the general population aged 40–49 years is approximately 1.2%.
The results showed that 15 out of 100 runners (15%) had advanced adenomas—over 10 times higher than the benchmark—and 39 out of 100 had at least one adenoma of any type. Most cases occurred in runners with very high training exposure (multiple ultramarathons or more than 15 races completed). A few cases even showed high-grade dysplasia, which is one step away from colorectal cancer.
The authors hypothesize that long-distance running, especially at extreme volumes, can cause repeated gastrointestinal ischemia (low blood flow to the gut), leading to chronic injury and inflammation. This recurring “microtrauma” might accelerate carcinogenic changes that lead to the development of precancerous adenomas.
What this means for runners
For most of us, running is protective against colon cancer, rather than being harmful. However, at the extreme end—multiple marathons and ultramarathons per year—the risk profile might shift (emphasis on ‘might’). If you’re logging big miles, racing often, and concerned about your cancer risk, it may be wise to get colon cancer screening earlier than standard guidelines and pay attention to persistent GI symptoms.
It’s also crucial to note some limitations. This was a relatively small, single-center study, with a limited number of cases. It doesn’t prove causation—nutrition, genetics, or other lifestyle factors may also play a role (the authors said they plan to report on participant characteristics in the future). Still, the difference compared to population norms is sufficient to warrant some concern, but we need to wait for the full peer-reviewed study before drawing grand conclusions.
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