Timothy Cannon Links Marathon Study to 15 Percent Advanced Adenomas

A marathon study of young extreme endurance runners found 15 percent had advanced adenomas, a rate that stood out enough to send researchers back for a bigger look. The small study focused on runners ages 35 to 50 and is already shaping a planned follow-up with a non-running control group.

Timothy Cannon’s 2019 Pattern

Timothy Cannon first noticed the possible pattern in 2019 after treating three unusually young patients with advanced colon cancer within six months. Two were in their 30s and one was in their 40s, and all three were extremely prolific runners who regularly competed in ultramarathons or multiple marathons despite lacking known risk factors.

That observation led him and other researchers to study 94 runners who had completed at least five marathons or two ultramarathons. Colonoscopies found nearly half had colonic polyps, and 15 percent had advanced adenomas more closely associated with cancer development.

Why The Study Stayed Preliminary

The result should be read carefully. The study had no non-runner control group, so it cannot separate a running effect from the possibility that the runners themselves were unusually high-risk in some other way.

Cannon said, "We don’t know at this point," when asked whether the runners themselves or the exercise could explain the finding. He added, "But I do think there’s a signal here" and "and it’s worth paying attention to." Possible explanations mentioned in the research include blood being shunted away from the gut, inflammation, and repeated irritation of the intestinal lining.

Amy S. Oxentenko’s Caution

Amy S. Oxentenko called the work "a super interesting study," but also "quite preliminary" and "only hypothesis-generating," then warned, "Runners shouldn’t panic." She also said, "Don’t let anyone tell you that rectal bleeding is normal for runners. Get it checked."

Researchers are planning a follow-up study with about 300 runners and a non-running control group. That next phase will look at genetics, diet, gut microbiome, and other endurance sports, which should give runners a clearer answer than this first pass can provide.

Eric McGlinchey and runner symptoms

Eric McGlinchey, one of the study participants, said, "We’ve all been there," referring to digestive distress in endurance sports. Sara Campbell, a Rutgers University researcher, warned that "the worst outcome would be for people to start thinking that running is bad for you," adding that "running is good for you and, most of the time, good for your gut."