Marathon Running and Colorectal Cancer: A Surprising Connection

A recent study has revealed a potential health risk for some of the world’s most fit individuals. Research suggests there may be a link between marathon running and an increased risk of colorectal cancer.

Conducted by oncologists at the Inova Schar Cancer Institute in Virginia, the study focused on relatively young long-distance runners. Surprisingly, these individuals exhibited a significantly higher occurrence of dangerous adenomas—a type of polyp—than would typically be expected for their age. While these findings are initial and need further investigation, they could indicate a notable connection between extreme physical activity and colorectal cancer.

“There’s definitely a signal here,” said David Lieberman, a gastroenterologist and professor emeritus at Oregon Health and Science University, who was not involved in the research. He remarked that the elevated rates of high-risk adenomas in such a young demographic was unexpected.

Unraveling an Unexpected Trend

The lead researcher, Timothy Cannon, had his interest piqued after treating three young patients diagnosed with colorectal cancer, all of whom were ultramarathon runners—races that exceed 26.2 miles. Notably, these patients were not just physically fit; they also fell well below the typical age range for such diagnoses, with the oldest being only 40.

In 2022, Cannon and his team began their prospective study, recruiting endurance athletes who had completed at least two ultramarathons or five regular marathons, all while having no family history of colorectal cancer or other significant risk factors. They ultimately examined the colons of 100 athletes aged 35 to 50 through colonoscopies.

The researchers specifically searched for advanced adenomas—larger or atypical polyps. While benign in themselves, these polyps have a higher risk of evolving into cancer than more common types. In comparing the findings among these athletes to historical data, they discovered something startling.

Roughly 1.2% of the general population in their 40s at average risk might be expected to have advanced adenomas. In stark contrast, a striking 15% of the runners in this study had these polyps, with nearly half having polyps of any kind.

The researchers suggested that “consideration of refined screening strategies for this population is warranted.”

Yet to Be Fully Understood

This research was presented earlier this year at the American Society of Clinical Oncology’s annual conference, which means it hasn’t undergone the rigorous peer-review process yet. The authors are quick to clarify that their findings do not definitively prove that endurance running is a direct cause of colorectal cancer.

If this connection is proven causative, a fundamental question arises: why? As even casual joggers might attest, running can sometimes lead to gastrointestinal issues, colloquially known as runner’s diarrhea. These incidents may stem from temporary reductions in blood flow to the intestines, which could harm adjacent cells. The researchers speculate that extreme runners, frequently facing this blood flow reduction, may develop chronic inflammation, potentially heightening the risk of cancer.

However, this is currently just one theory about what’s happening. Future studies are necessary to confirm these findings and explore the causes and risk factors that could elucidate this possible increase in risk.

Despite this research, there’s no reason for runners or those engaged in other forms of cardio to panic. The numerous health benefits of regular exercise—including a decreased risk of various cancers—still far outweigh the risks for the average person.