Long-distance running, once seen as a symbol of health and fitness, may carry unexpected risks, according to a new study. Researchers from Virginia’s Inova Schar Cancer Institute found evidence suggesting that intense endurance training, such as running marathons and ultramarathons, could lead to increased cancer risk. The study, presented at the 2025 American Society of Clinical Oncology (ASCO) Annual Meeting, reveals that 41% of participants had at least one precursor to colon cancer, known as an adenoma, which is significantly higher than the average for their age group.
Dr. Timothy Cannon, one of the researchers, noted the discovery of a surprising link between long-distance running and the development of advanced adenomas. While the study was not peer-reviewed and lacks a control group, the data is still concerning. The participants, all between the ages of 35 and 50, had completed at least five marathons or two ultramarathons and had no known family history of cancer or other risk factors. This suggests that the observed effects might be specifically tied to the extreme exercise regimens.
The study’s findings underscore the importance of recognizing potential health risks associated with ultra-endurance activities. While the exact causal relationship between running and the development of polyps needs further investigation, the results have raised questions about the long-term effects of such training. The researchers emphasize that running, while potentially risky for the colon, remains essential for overall health and should not be discouraged entirely. They caution that runners, especially those completing extreme distances, should be vigilant about symptoms such as rectal bleeding, persistent diarrhea, or chronic abdominal pain and consult a medical professional if these symptoms arise.
In a related development, experts are also cautioning that the findings are not definitive and must be interpreted with care. The study lacked a control group, which limits its ability to establish a direct cause-effect link between running and cancer risk. This is an important caveat, as it means the study is still in its early stages and could be subject to further validation. However, the data is still relevant in sparking a conversation about the health impacts of endurance sports.
Despite the study’s limitations, the results have raised questions about the long-term health effects of extreme running. While the researchers acknowledge that more studies are needed, the data is significant enough to warrant a shift in how we view these activities. The team is now planning to explore other factors that could contribute to these outcomes, such as genetic predispositions, diet, and lifestyle.
For now, the key takeaway is that while running remains a vital part of a healthy lifestyle, runners, especially those training for ultra-distance events, must be aware of the potential risks. It is important to remember that the study’s findings do not mean running is harmful, but rather that extreme running may bring with it certain health challenges that need to be managed carefully.
Ultimately, the study aims to foster a better understanding of the health impacts of long-distance running and encourage runners and medical professionals to work together to mitigate any potential risks. By raising awareness, the researchers hope to contribute to a more informed approach to fitness and health, ensuring that the benefits of exercise are balanced with a realistic understanding of its risks.