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POTENTIALLY TRUE (for extreme endurance runners)<\/strong><\/p>\n A groundbreaking study has revealed a potential link between extreme endurance exercise and increased risk of advanced colon cancer in younger adults, though experts stress the findings are preliminary and require further research.<\/p>\n Dr Timothy Cannon, an oncologist at Inova Schar Cancer Institute in Virginia, launched the study after noticing a disturbing pattern: multiple ultramarathoners were presenting with advanced-stage colorectal cancer.<\/p>\n The study recruited 100 long-distance runners aged 35 to 50 who had completed either at least five marathons or two ultramarathons to undergo colonoscopy screening.<\/p>\n Participants with hereditary cancer syndromes or inflammatory bowel disease were excluded to focus on the potential impact of endurance exercise alone.<\/p>\n The results were striking: almost 50% of participants had polyps, whilst 15% had advanced adenomas – pre-cancerous growths with a high chance of progressing into cancer.<\/p>\n By comparison, recent studies suggest that only around 4.5% to 6% of adults in their late 40s in the general population have such advanced adenomas.<\/p>\n The findings even exceeded the 12% prevalence seen amongst Alaska Natives, who are unusually prone to colon cancer.<\/p>\n “This is the first prospective study we know of to explore whether exercise-induced intestinal stress – specifically bowel ischemia from long-distance running – might increase cancer risk,” Dr Cannon said.<\/p>\n “While the results don’t prove causation, they strongly suggest that intense endurance exercise could be a meaningful risk factor for colorectal cancer and warrants further study,” he added.<\/p>\n The mechanism behind this potential link may involve exercise-induced gastrointestinal injury, believed to be associated with reduced blood flow to the intestines during long-distance running.<\/p>\n During intense endurance exercise, blood is diverted from the colon to fuel legs and other muscles, temporarily starving gut tissue of oxygen.<\/p>\n This condition, known as ischaemic colitis, can cause swelling, bleeding and is often dismissed by runners as normal “runner’s trots” or “runner’s colitis”.<\/p>\n “There’s no proof that ischaemic colitis causes cancer,” Dr Cannon said.<\/p>\n “But it’s not hard to imagine how it would. When you have so many cells dying and then growing back in a disorderly and unregulated way, there are lots of opportunities for DNA replication errors.”<\/p>\n Repeated cycles of cell damage and repair could theoretically create conditions that allow mutations to develop, leading to cancer.<\/p>\n However, experts urge caution in interpreting these results, as the study was small, had no control group of non-runners and has not yet been peer-reviewed or published in a medical journal.<\/p>\n Dr Marianna Zeichen of Jackson Medical Group emphasised that “the sample size of 100 participants is limited, and the findings demonstrate an association rather than a causal relationship”.<\/p>\n The correlation could be due to several factors, such as common lifestyle habits amongst long-distance runners or family medical histories, which weren’t fully explored.<\/p>\n Importantly, this research applies only to extreme endurance athletes, not regular exercisers or moderate runners.<\/p>\n Epidemiological studies consistently show that physically active people have lower cancer incidence, including fewer colon polyps and lower rates of colorectal cancer.<\/p>\n “I definitely don’t want people to come away saying exercise is not good, because it is good,” Dr Cannon stressed.<\/p>\n “The question is whether there is a dose of exercise that is so high that it actually increases your risk of colon cancer. And I believe there is.”<\/p>\n Dr Cannon advises that any bleeding from runners should be a reason to get a colonoscopy, not something to be ignored or dismissed as normal.<\/p>\n The findings were presented at the 2025 American Society of Clinical Oncology Annual Meeting in Chicago and received widespread media coverage, including in The New York Times.<\/p>\n \u00a0<\/p>\n References:<\/strong><\/p>\n 1. https:\/\/ascopubs.org\/doi\/10.1200\/JCO.2025.43.16_suppl.3619<\/a><\/p>\n 2. https:\/\/www.inovanewsroom.org\/press-release\/2025\/08\/groundbreaking-inova-study-finds-potential-link-between-long-distance-running-and-colon-cancer\/<\/a><\/p>\n 3. https:\/\/www.sciencefocus.com\/news\/ultra-running-colon-cancer<\/a><\/p>\n 4. https:\/\/www.foxnews.com\/health\/long-distance-running-tied-higher-risk-colon-cancer-early-study-suggests<\/a><\/p>\n 5. https:\/\/www.advisory.com\/daily-briefing\/2025\/08\/25\/marathon-cancer<\/a><\/p>\n 6. https:\/\/jacksonhealth.org\/marathons-and-extreme-running-can-it-increase-your-risk-of-colon-cancer\/<\/a><\/p>\n