A recent study presented at the 2025 American Society of Clinical Oncology (ASCO) Annual Meeting in Chicago, involving 100 runners aged 35 to 50 that ran from October 2022 through December 2024 has suggested a link between high-level distance running and colon cancer. The study, which was designed by co-director of the Gastrointestinal Cancer Program at the Inova Schar Cancer Institute, Timothy Cannon, MD, included runners who had completed at least two ultramarathons or five regular marathons that, according to Cannon, “were otherwise healthy and had no known genetic predisposition or inflammatory conditions.” While polyps that have a high chance of turning into cancer range from being about 5-6% in adults in their 40s, a surprising 15% of the athletes that received colonoscopies during the study turned up with these polyps, and 41% had at least one, intriguing experts, but requiring more examination before definitive conclusions are made.
Cannon was prompted to conduct this study due to a pattern he noticed in his patients — more specifically, that three patients who were young, extremely long-distance athletes all had stage IV colon cancer. Recruitment for the study was made with the assistance of the wives of two of the deceased runners, which ultimately yielded 100 long-distance athletes who had never received a colonoscopy up until that point. Those with hereditary cancer syndromes or inflammatory bowel disease were not included in order to better isolate the potential impact of the endurance exercise by itself. Before undergoing the procedure, the athletes were instructed to complete a questionnaire covering dietary habits, bowel history, and long-distance running patterns to better identify possible links between the increased rate of polyps in the group. All polyps that were identified during the study were reviewed by a panel of gastroenterologists, pathologists, and oncologists who determined that they met the criteria for advanced adenomas (polyps).
Hypotheses have been proposed by Cannon to explain this phenomenon prior to further study, including that ischemic colitis — when blood flow to the colon is temporarily reduced and directed to the muscles during intense activity — could be a cause. It is suggested that this process, although typically not lasting long and self-reforming (though it does cause damage and swelling), could contribute to repeated cycles of cell damage and repair that may allow mutations to occur as a result of faulty cell divisions that can cause cancer. However, there is no current evidence that people with ischemic colitis are at a greater risk of colon cancer, so currently this proposal remains purely speculative.
While the study has received Institutional Review Board (IRB) approval, there are some important caveats to be considered. The first is that it has yet to be published in a peer-reviewed journal, and that it was small and specific to endurance athletes with limited information about their other possible cancer risk factors. Additionally, the study failed to provide a comparison group of non-runners, with the rate of polyps in non-runners in the same age range being drawn from other studies performed in the past. In fact, despite findings, a lot of previously published research has suggested that physical activity may, in fact, prevent cancer as well as other chronic diseases and health problems, with people who jog for just 10 minutes a day having a reduced risk of death from dying from causes like heart disease, according to a study from 2014. With this being said, however, what especially stands out from the studied individuals is that their average age was 42.5 years old, which is two and a half years below the recommended age of 45 years for a first screening of colonoscopy after it had been previously lowered from 50.
Currently, further research is underway to analyze dietary factors, training regimens, and other lifestyle habits to better understand the relationship between distance running and cancer. Notwithstanding the current results, Canon claims, “the bigger problem with our health is we don’t exercise enough…people should keep exercising, for sure,” and to stay up to date on colon cancer screenings if you experience unusual symptoms such as stomach cramps or blood in stool, and log a lot of miles. Reflecting on the study, he explains how “if we can identify these cancers earlier in people who otherwise wouldn’t meet current screening criteria, we can save lives.”
