Long-distance running is a popular activity among the health-conscious, but recent research suggests it may be linked to a higher risk of colon cancer in certain demographics. A comprehensive study has revealed that individuals aged 35 to 50 who regularly participate in marathons may be more susceptible to developing precancerous tumors in their colon, known as adenomas, which can be precursors to cancer.
In a pivotal study conducted by scientists in Washington, D.C., it was found that out of 100 participants, a striking 41 percent had at least one adenoma, a benign tumor that has the potential to evolve into colon cancer. Additionally, 15 percent of those studied had advanced adenomas, indicating more serious growths. Alarmingly, over half of these individuals reported experiencing rectal bleeding, a significant warning sign of colon cancer.
Dr. Timothy Cannon, the medical oncologist leading the research, highlighted that these results are concerning, as they exceed typical expectations for the general population. He emphasized the importance of screening for colon cancer, advising any long-distance runners who experience symptoms like rectal bleeding to seek testing, regardless of their age.
The study, although observational, raises questions about whether long-distance running itself increases cancer risk or if other lifestyle factors, such as diet, contribute. Dr. Cannon speculated that prolonged running may redirect blood flow away from the colon to the legs, potentially leading to cell death and mutations that could initiate cancer development. He stated, "As a colon cancer oncologist, I had seen several patients die of colon cancer in their 30s who ran ultramarathons, which are 50 km or longer."
Infarcts, which are areas of dead tissue resulting from a loss of blood supply, can occur during long-distance running. When blood flow is significantly reduced—typically due to clots or narrowed vessels—the affected tissue fails to receive the necessary oxygen and nutrients, ultimately leading to cell death. This phenomenon could be part of the explanation for the increasing rates of colon cancer among younger individuals.
Statistics reveal a troubling trend: those born in the 1980s face double the risk of being diagnosed with colon cancer compared to previous generations. Young patients, often surprised by their diagnoses, include individuals like Laurie Koshers, a vegetarian who ran daily, and marathon runner John B. Johnson, both of whom were diagnosed with colon cancer in their 40s and 30s, respectively.
The recent study was conducted in memory of two marathon runners who battled colon cancer, Josh Wadlington and Spencer 'Trigg' Robbins. It involved participants aged 35 to 50 who had completed at least two marathons of 50 kilometers (31 miles) or more, or five marathons of at least 42 kilometers (26.2 miles). Those with inflammatory bowel disease or other conditions linked to colon cancer were excluded from the study.
Participants had an average age of 42 years and consisted of 55 percent females, reporting weekly running distances of approximately 32 to 64 kilometers (20 to 40 miles). Between October 2022 and December 2024, these individuals underwent colonoscopies to screen for colon cancer.
Preliminary findings indicate that many runners consumed highly processed foods, such as energy bars and gels, daily. Dr. Cannon noted the potential connection between these dietary habits and an increased risk of colon cancer. He stressed the importance of seeking medical advice if any runner experiences rectal bleeding, urging individuals to consider a colonoscopy even if they are below the typical screening age.
Dr. Cannon remarked, "Bleeding from the rectum in runners is often dismissed due to conditions like runners' colitis, but awareness needs to grow so that those who experience bleeding seek further evaluation." Most of the participants in the study with advanced adenomas reported blood in their stools, highlighting the need for increased vigilance.
The American Cancer Society projects that over 154,000 Americans will be diagnosed with colorectal cancer this year, with approximately 20,000 of those cases being in individuals under 50. Although this aligns with figures from two decades ago, diagnoses in younger populations are rising sharply—early-onset colon cancer cases are expected to increase by 90 percent among those aged 20 to 34 between 2010 and 2030, with rates in teens surging by 500 percent since the early 2000s.
