A study has found that colon polyps (adenomas) were detected at a higher rate among young and healthy marathon and ultramarathon athletes compared to the general population. This suggests a potential link between extreme endurance exercise and the risk of colon cancer.

According to the New York Times (NYT) on August 19 (local time), Dr. Timothy Cannon of the Inova Schar Cancer Institute in Fairfax, Virginia, recruited 100 marathon and ultramarathon athletes and conducted colonoscopy screenings. The motivation for the study was three patients under the age of 40 who had been diagnosed with colon cancer. All three were slim and exercised regularly. Two of them regularly ran 100-mile (about 160 km) ultramarathons, and the other had completed 13 half marathons in a single year.

The results showed that about half of the study participants were found to have adenomas, which are considered precursors to colon cancer, and 15% were confirmed to have advanced adenomas, which have a higher risk of progressing to cancer. These rates are higher than those seen in the general population in their late 40s (4.5-6%) or among Alaska Natives, who have a high incidence of colon cancer (12%). The study was presented at the American Society of Clinical Oncology annual meeting but has not yet been published in a scientific journal.

Marathon and Ultramarathon Athletes
100 Undergo Colonoscopy Screening

Half Found to Have Precancerous 'Adenomas'
15% Confirmed with 'Advanced Adenomas'
Higher Rate than General Population

Lack of Exercise is a Bigger Issue
Extreme Exercise Increases Colon Cancer Risk
Potential Link Cannot Be Ruled Out

No Control Group and Family History Not Verified
No Need to Stop Running

People Running Marathons (Unrelated to Article Content). Pexels

Laura Linville (47), a marathon runner from Alexandria who participated in the study, said, "Running is usually associated with positive effects like weight control and stress relief, so I didn't expect a bad result." She explained that seven polyps were found during her colonoscopy and she needed additional surgery, but she would not give up running and would continue to get regular screenings.

This study was released amid growing concerns about the increasing rates of colon and rectal cancer among adults under 50. The NYT noted, "In 2021, the United States lowered the recommended age for a first colonoscopy in average-risk groups from 50 to 45," and added, "However, the medical community is perplexed as cases of cancer are being detected in healthy young people."

Dr. Cannon said, "For most people, lack of exercise is a bigger problem, so I can't discourage exercise," but added, "Based on my patients' cases and the study results, I cannot rule out the possibility that extreme exercise may increase the risk of colon cancer."

However, experts pointed out that this study has limitations, such as the absence of a control group and insufficient information on participants' family history. They also explained that endurance athletes may have overlooked symptoms like diarrhea, bloody stools, or abdominal pain, attributing them to 'runner's trots'-the sudden urge to defecate during running.

David Rubin, a professor of gastroenterology at the University of Chicago, noted, "Rather than extreme exercise itself being the cause, it's possible that some started running because they had a family member with cancer." Eric Christensen, an assistant professor of oncology at Johns Hopkins University School of Medicine, emphasized, "There is no need to stop running," and added, "If you have symptoms, don't hesitate to tell your doctor, regardless of how healthy you may appear to others."

One of the patients who inspired this study was Josh Waddington, a geographer. He participated in ultramarathons two or three times a month and even took on the 'Savage Seven,' running a marathon every day for seven days. However, despite repeated bloody stools and abnormal blood tests, he dismissed them as mere side effects of running. Ultimately, he was diagnosed with colon cancer in his late 30s in 2018 and passed away in 2021 at the age of 41. The other two patients also died.

Waddington's wife said, "He never drank or smoked and followed a vegan diet. He was always the picture of health," and added, "I regret ignoring so many warning signs. We believed we were living the right way, so we brushed off his symptoms."