Study Finds High Rate of Precancerous Colon Polyps Among Marathon Runners

A recent study published in Cancer Epidemiology revealed that nearly half of marathon and ultramarathon runners examined were diagnosed with adenomas, precancerous polyps in the colon, despite having no symptoms, known risk factors, or family history of colorectal cancer. Approximately 15 percent of these athletes had advanced adenomas, which carry a higher risk of developing into colorectal cancer. The study involved 94 runners aged 35 to 50 who had completed at least five marathons or two ultramarathons and underwent colonoscopy screenings as part of the research protocol.

The findings surprised researchers, as the prevalence of adenomas among these runners was significantly higher than the estimated 4 to 6 percent found in the general population of the same age group. Adenomas are benign growths that can become malignant over time, making colonoscopy a critical preventive tool for early detection and removal of polyps.

The study originated from observations by Dr. Timothy Cannon, an oncologist at the Inova Schar Cancer Institute in the U.S., who noted three relatively young marathon runners diagnosed with advanced colorectal cancer without typical risk factors. This prompted an investigation into whether prolonged endurance training might be linked to a higher incidence of precancerous polyps.

Researchers hypothesize that repeated long-duration exercise may reduce blood flow to the digestive system, causing repeated injury and inflammation to the intestinal lining, potentially promoting polyp formation. Other theories include chronic physiological stress, changes in gut microbiota, and cumulative effects of extreme training loads. However, the study does not establish a causal relationship, and further large-scale, controlled studies are needed.

Dr. Ronen Brenner, head of oncology at Wolfson Medical Center, emphasized that while the findings raise important questions, they do not warrant stopping endurance running or changing current health recommendations. He stressed the importance of awareness and early diagnosis, noting that even very healthy individuals, including athletes, are not immune to colorectal cancer. Early detection significantly improves treatment outcomes, and advanced therapies are available even for metastatic disease, allowing personalized treatment and improved quality of life.