Although it may seem contradictory, running long distances, such as marathons and ultramarathons, will not always be healthy, as we believed. We bring this up following the results of a recent study led by Dr. Timothy Cannon of the Inova Schar Cancer Institute, which found that long-distance runners have a significantly increased risk of colon cancer.

This research was presented at the American Society of Clinical Oncology Annual Meeting in Chicago in 2025. The researcher's concern arose after noticing that ultramarathoners under the age of 40 were showing signs of advanced colon cancer.

After this, Cannon launched a study of runners who had completed at least five marathons or two ultramarathons, excluding those with a family history or other known risk factors.

“The study supports the hypothesis that extreme endurance runners have an increased risk of precancerous polyps,” the researcher told Fox News Digital.

Shocking Results

The study included 100 participants between the ages of 35 and 50 who had completed at least five marathons or two ultramarathons. They underwent colonoscopies, and examinations revealed that 15 percent had advanced adenomas, compared with the normal rate of 1–2 percent for this age group. They also completed a survey about their eating habits, bowel history, and long-distance running patterns.

Forty-one percent of participants were identified as having at least one adenoma, raising concerns about the gut health of runners.

Importantly, all of these growths discovered during the procedures were reviewed by a panel of gastroenterologists, pathologists, and oncologists to determine if they met criteria for advanced adenomas.

Of note, the average age of participants was 42.5 years,well below the typical detection age of 45.

Link Between Intense Exercise and Intestinal Damage

Researchers suggest that intense resistance training may lead to repeated intestinal stress, causing damage that can result in mutations and the development of polyps over time.

Despite the alarming results, Dr. Cannon emphasizes that exercise remains beneficial and advises runners to pay attention to symptoms such as bleeding and persistent abdominal pain.

Warnings and Recommendations

Experts warn that runners should not ignore unusual symptoms such as rectal bleeding, urging them to seek medical attention if they occur. Although research suggests a possible risk associated with extreme exercise, continuing regular physical activity is crucial for overall health.

Recommendations for long-distance runners to mitigate this risk include:

These combined measures may help reduce the risk of developing polyps early and thus preventing their progression to colon cancer, while still taking advantage of the overall health benefits of exercise.

Other Health Risks Associated with Long-Distance Running

In addition to the results provided by the aforementioned study, which indicate certain effects, there are other health risks associated with long-distance running:

Although long-distance running provides benefits, doing so in an extreme manner and without adequate rest can carry risks for various body systems, so it is essential to control the intensity, duration, and recovery to minimize these dangers.