A new study signals a surprising connection between marathon-level endurance running and precancerous colon polyps — and experts want athletes to pay attention.
The Unexpected Finding Shaking Up the Running World
What started as a curious pattern in a cancer clinic may now have serious implications for endurance athletes. A small but striking study has uncovered unusually high rates of precancerous colon polyps in young, high-mileage runners — and while researchers are urging caution before drawing firm conclusions, the findings are impossible to ignore.
The story begins with oncologist Timothy Cannon, who co-directs the gastrointestinal cancer program at Inova Schar Cancer Institute. Back in 2019, he noticed something that gave him pause: within just six months, he had treated three unusually young patients with advanced colon cancer. Two were in their 30s, one in their 40s — and all three were devoted endurance athletes with no known risk factors. They regularly competed in ultramarathons and multiple marathons. That pattern was enough to send Cannon searching for answers.
What the Marathoners Study Found
Cannon and his team studied 94 runners between the ages of 35 and 50, each of whom had completed at least five marathons or two ultramarathons. When participants underwent colonoscopies, the results were eye-opening: nearly half had colonic polyps, and 15 percent had advanced adenomas — the type more closely linked to cancer development.
The critical question the study has yet to answer, however, is whether the researchers happened to select a high-risk group who also happen to be extreme runners, or whether the intense running itself is contributing to the elevated polyp rates. The study lacked a non-runner control group, making it impossible to draw a direct causal link at this stage.
Still, Cannon believes there may be something to investigate. There is a signal worth paying attention to, he says, particularly when it comes to how extreme running affects the body.
A Biological Theory Worth Watching
Researchers are exploring possible biological explanations for the connection. One theory suggests that prolonged endurance exercise may divert blood flow away from the gut, subjecting the intestinal lining to repeated cycles of stress, inflammation, and irritation. This mechanism could, in theory, increase mutation risk over time — though Cannon himself describes it as unproven.
It’s a theory that resonates with endurance athletes, many of whom are well-acquainted with gastrointestinal distress during long runs. Study participant Eric McGlinchey, who himself was found to have multiple non-advanced polyps, noted that digestive discomfort is simply part of the sport for many runners. McGlinchey was among those who learned about their polyps through the study — a discovery that, while unsettling, came with reassurance that the findings were not at an advanced stage.
Marathoners Shouldn’t Panic — But Should Stay Informed
Experts across the board are emphasizing one key message: this is not a reason to lace up your sneakers any less. Amy S. Oxentenko, a gastroenterologist who reviewed the findings, described the study as highly preliminary and called it hypothesis-generating rather than conclusive. She was clear that runners should not panic.
Sara Campbell of Rutgers University echoed that sentiment with equal conviction. The worst possible outcome of this research, she argued, would be for people to conclude that running is harmful. The overwhelming body of evidence still confirms that running is beneficial for overall health — and most of the time, beneficial for gut health specifically.
That said, both Oxentenko and Cannon agree on one thing: athletes should not dismiss symptoms. Rectal bleeding, persistent cramping, and unusual digestive issues are not simply par for the course. Anyone experiencing these symptoms should consult a healthcare provider rather than assuming they’re just side effects of training.
What Comes Next for Marathoners Research
The study is far from the final word. Researchers are now planning a significantly larger follow-up involving approximately 300 runners alongside a non-running control group. That expanded study will examine a range of variables including genetics, diet, and gut microbiome, and will explore whether the findings are specific to running or tied more broadly to intense, long-term endurance exercise of any kind.
For now, the takeaway is this: keep running, stay informed, and listen to your body. The science is still unfolding — but it’s asking questions that athletes and their doctors should be asking, too.
Source: INDEPENDENT
