#Ultramarathon

A beloved physical activity endorsed by millions for its health benefits—long-distance running—may be unexpectedly associated with a higher risk of developing precancerous colon growths among young adults, according to a new study presented at the prestigious American Society of Clinical Oncology (ASCO) 2025 conference in Chicago. The study, conducted by researchers based in Washington, DC, challenges the prevailing wisdom that vigorous aerobic exercise is universally protective against all forms of cancer, raising pressing questions for health-minded Thais—especially the country’s growing cohort of marathon and ultramarathon enthusiasts.

A widely celebrated form of exercise, long-distance running, may be linked to an unexpected risk among certain young adults. A study presented at ASCO 2025 in Chicago found a higher-than-expected rate of colon adenomas—precancerous growths—in adults aged 35 to 50 who regularly run ultramarathons or multiple marathons. The results prompt careful discussion for health-minded Thai runners, where endurance events have surged in popularity in recent years.

The investigation examined 100 runners who completed at least two ultramarathons (over 50 km) or five standard marathons (42 km) within a defined period. Among participants, 41% had at least one adenoma and 15% had advanced adenomas. These rates appeared higher than typical figures for the general population. About half of those with advanced lesions reported rectal bleeding, a symptom sometimes mistaken for benign exercise-related issues such as runner’s colitis.