Long-Distance Running Linked to Increased Cancer Risk

Interestingly, long-distance running, including marathons and ultramarathons, might not be the health boost we once believed. A new study from Virginia suggests that it may actually heighten the risk of cancer.

Dr. Timothy Cannon from the INOVA Schar Cancer Institute has initiated research that will be presented at the 2025 American Society of Clinical Oncology (ASCO) Annual Meeting. His interest was piqued when he noted that ultramarathoners under 40 had been diagnosed with advanced colon cancer.

With a focus on runners, he examined participants who had completed a minimum of five marathons or two ultra marathons, excluding family histories and other established risk factors.

Examining Diet’s Role in Colon Cancer Risk

The study analyzed 100 individuals aged 35 to 50 who had never undergone a colonoscopy but had run at least five marathons or two ultra marathons. Those with hereditary cancer syndromes or inflammatory bowel diseases were excluded to isolate the potential impacts of endurance exercise.

“This study supports the theory that extreme endurance running increases the risk of precancerous polyps,” Dr. Cannon observed.

Participants participated in a colonoscopy and completed surveys on their dietary habits, medical histories, and long-distance running experiences.

Surprisingly, 15% of the runners were found to have advanced adenomas, which are precancerous growths, compared to the usual 1-2% in that age group. Alarmingly, 41% exhibited at least one adenoma.

Growths identified during the colonoscopy were evaluated by a team of gastroenterologists, pathologists, and oncologists to assess whether they fit the criteria for advanced adenomas.

Unexpected Findings in Runners

Dr. Cannon expressed his surprise at the prevalence of polyps among the runners. “I anticipated finding more adenomas than usual for their age, but I never thought 15% would have advanced adenomas,” he admitted.

The average age of participants was 42.5, while routine screenings typically start at age 45.

Cannon and other specialists postulate that rigorous endurance training may induce repeated “gut stress.” When running long distances, blood flow diverts away from the intestines, which could lead to damage and inflammation, potentially resulting in mutations and polyps over time.

The Need for Caution

Experts urge caution, as the study’s results are not definitive. There was no control group, and it hasn’t yet been peer-reviewed, prompting questions about potential biases. Moreover, the runners were largely from the Washington, DC area, suggesting they might share other common risk factors unrelated to running.

He also acknowledged that the lack of detailed family history may have influenced the results.

Physical Activity Still Essential

Despite these findings, Cannon underscores the importance of exercise. “People should absolutely keep exercising,” he insisted. “The risks associated with not exercising far outweigh any risks from exercising excessively.” He reiterates that while extreme activities may pose some cancer risk, regular exercise still plays a crucial role in reducing cancer risks.

For those undertaking extreme distances, it’s vital to be aware of symptoms like bleeding, ongoing diarrhea, and abdominal pain.

Bleeding after a run should not be brushed off as normal; anyone experiencing this should seek medical advice. Dr. Cannon pointed out that some gastroenterologists almost dismiss reports of bleeding as a typical occurrence after long runs.