A rise in early onset colorectal cancer

Colon and rectal cancer are climbing among adults under 50, a group once thought to be at low risk. While older adults still account for most cases, the increase in early-onset colorectal cancer prompted a change in screening guidelines in 2021, lowering the recommended age for a first colonoscopy from 50 to 45, for those at average risk.

These shifts made three of oncologist Timothy Cannon's patients stand out. The patients were young, lean, and physically active — including two ultramarathoners and a runner who had completed 13 half-marathons in a year. Yet all three patients developed advanced colon cancer, despite having no known risk factors.

Cannon, who practices oncology at Inova Schar Cancer, said he was struck by the cases and wondered whether extreme endurance running could play a role.

Study details

For the study, Cannon recruited 100 marathon and ultramarathon runners aged 35 to 50 to undergo colonoscopies. The results were stark. Almost half of participants had polyps, and 15% had advanced adenomas likely to become cancerous.

This prevalence of advanced adenomas was much higher than the 4.5% to 6% typically seen among adults in their late 40s in the general population, according to recent studies, and even exceeded the 12% seen among Alaska Natives, who are unusually prone to colon cancer.

The findings were presented at an American Society of Clinical Oncology conference but have not yet been published in a medical journal.

For some participants, the outcome was a shock.

"I was surprised — you would think running is super healthy," said Laura Linville, a 47-year-old woman who has run marathons for years and took up ultramarathon running during the pandemic. Linville learned she had seven polyps, including some so large she needed additional procedures.

"Running is typically associated with better body mass and lower stress and lots of other positives — you never hear it's bad for you," she said. Although Linville currently has no intention of giving up marathons, she said she would get checked for signs of colon cancer more often.

According to Rubin, endurance runners may dismiss red-flag symptoms of colon cancer, such as bloody stools, bowel urgency, and diarrhea, attributing them to benign conditions like "runner's trots." These symptoms can be caused by ischemic colitis, which occurs when blood is diverted from the colon to muscles during intense exercise, temporarily reducing oxygen and causing inflammation. While ischemic colitis usually improves on its own, some experts hypothesize that repeated cycles of cell damage and repair could allow mutations to develop, leading to cancer.

Although there is currently no evidence that people with ischemic colitis have an increased risk of colon cancer, health experts recommend that runners get evaluated by a physician if they experience symptoms, like stomach cramps or loose or bloody stools.

"I wouldn't necessarily tell people to stop running; I would tell them to run," said Eric Christenson, an assistant professor of oncology at Johns Hopkins School of Medicine. "But this reinforces the importance of listening to your body. If you have symptoms, say something, even if people look up to you as a picture of health."

Josh Wadlington, an ultramarathoner and one of the patients who inspired Cannon's study, illustrates the stakes. Wadlington, a geographer who once ran seven marathons in seven days, often experienced bloody stools and occasionally had abnormal blood tests but dismissed them as a side effect of endurance running. In 2018, Wadlington was diagnosed with colon cancer in his late 30s and later died in 2021 at age 41.

"He didn't drink, he didn't smoke, he was vegan. He was always fit," his widow said. "We noticed, looking back, how many things we brushed off. But you ignore signs you shouldn't because you think you're doing everything right."