Ran Marathons to Get Healthier, but Faced Higher Colorectal Cancer Risk, Study Finds

Small-Scale Study of 100 Marathon and Ultramarathon Runners
"Half Found with Adenomas... 15% Had Advanced Adenomas"

A study has found that young and healthy marathon and ultramarathon runners have a higher rate of colon adenomas (glandular polyps) compared to the general population. This suggests a potential link between extreme endurance exercise and the risk of colorectal cancer.

People running a marathon. Stock photo unrelated to the article content. Pexels

According to The New York Times on August 19 (local time), Dr. Timothy Cannon of the Inova Schar Cancer Institute in Fairfax, Virginia, recruited 100 marathon and ultramarathon runners to undergo colonoscopies. The study was prompted by three patients under the age of 40 who had been diagnosed with colorectal cancer. All three were slim and exercised regularly. Two routinely ran 100-mile (about 160 km) ultramarathons, while the other had completed 13 half-marathons in a single year.

Colonoscopies of 100 runners revealed adenomas in half

The results showed that about half of the study participants had adenomas, which are considered precursors to colorectal cancer, and 15% had advanced adenomas with a high potential to develop into cancer. These figures are higher than those found in the general population in their late 40s (4.5-6%) or among Alaska Natives, who have a high incidence of colorectal cancer (12%). The study was presented at the American Society of Clinical Oncology conference but has not yet been published in a scientific journal.

Laura Linville, a 47-year-old 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 negative result." She shared that seven polyps were found during her colonoscopy, requiring additional surgery. She added that while she will not give up running, she will continue to get regular checkups.

This study was released amid growing concern over the increasing incidence of colorectal and rectal cancer in adults under 50. The New York Times noted, "In 2021, the United States lowered the recommended age for a first colonoscopy for average-risk individuals from 50 to 45," adding, "However, the discovery of cancer among healthy young people is leaving the medical community perplexed."

Dr. Cannon stated, "For most people, lack of exercise is a bigger problem, so I can't advise against exercise." However, he also said, "Based on my patients' cases and the study results, I cannot rule out the possibility that extreme exercise may increase the risk of colorectal cancer."

Study limitations: lack of control group, unconfirmed family history... "No need to stop running"

However, experts pointed out that the study had limitations, such as the absence of a control group and insufficient information about the participants' family histories. They also explained that endurance athletes often experience symptoms such as diarrhea, bloody stools, and abdominal pain, which could have been dismissed as "runner's trots" (the urge to defecate suddenly during running) rather than warning signs.

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

One of the patients who inspired the study was Josh Waddington, a geographer. He was an enthusiastic runner, participating in ultramarathons two or three times a month and even attempting the 'Savage Seven,' which involves running a marathon every day for seven days. However, despite repeated bloody stools and abnormal blood test results, he dismissed them as simple side effects of running. Ultimately, he was diagnosed with colorectal 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," adding, "I regret ignoring so many warning signs. We believed we were living the right way, so we downplayed his symptoms."