New research recently presented by Dr. Timothy Cannon in a poster session at the 2025 American Society of Clinical Oncology conference is seeking to understand whether ultramarathon running is a risk factor for colorectal cancer.
Dr. Cannon, an oncologist who works at Inova Schar Cancer Institute in Fairfax, Virginia, and his colleagues initially had the idea for this study after seeing several clinical cases of ultramarathoners with advanced colorectal cancer. They state in the study's abstract that, while "exercise induced gastrointestinal injury is believed to be associated with reduced blood flow to the intestines during long distance running," to this date there had been no research linking "exercise-induced bowel ischemia to carcinogenesis."
Their research, then, sought to determine if there was a connection, and, more specifically, to evaluate the risk of advanced adenomas (AA) — which are linked to increased risk of colorectal cancer and colorectal cancer-related death — in long-distance runners aged 35-50.
The researchers studied colonoscopy results collected from one hundred marathon and ultramarathon runners, and, as The New York Times puts it, "the results were staggering." The New York Times continues:
Almost half the participants had polyps, and 15 percent had advanced adenomas likely to become cancerous.
The rate of advanced adenomas was much higher than that seen among adults in their late 40s in the general population, which ranges from 4.5 percent to 6 percent, according to recent studies The figure among extreme runners was even higher than the 12 percent rate among Alaska Natives, who are unusually prone to colon cancer.
Thus, the researchers posit that, indeed, long-distance running appears to be a risk factor for developing advanced adenomas of the colon. The Results and Conclusions sections of the poster's abstract provide more details:
Results: Between October 2022 and December 2024, 102 subjects were screened, and 100 underwent colonoscopy as part of the study. The median age was 42.5 years; 55 of the participants were female and 45 were male. The historical benchmark used for expected AAs in average-risk individuals aged 40-49 years was 1.2%. Among the 100 subjects in this study, 15% (95% exact confidence interval: 7.9%- 22.4%) had confirmed AAs. 39 out of 100 subjects had at least one adenoma. Three additional subjects had three or more adenomas but did not meet our predefined criteria for AA and were not included among the 15 patients with AA.
Conclusions: NCT 05419531 [JS: the current study] achieved its predefined endpoint for advanced adenomas, suggesting that "intensive" long distance running is a risk factor for advanced adenomas of the colon. Consideration of refined screening strategies for this population is warranted. Future pathological and epidemiological evaluations should explore causation and ancillary risk factors in this unique population.
This study is timely, as there has also been a more general rise in colorectal cancer rates in young adults in recent years. The Cancer Research Institute describes these rates as "skyrocketing," explaining:
In the United States, colorectal cancer (CRC) is the third most diagnosed cancer and the third leading cause of cancer death in both men and women. The American Cancer Society (ACS) estimates that in 2025 alone, there will be 154,000 new cases of colorectal cancer diagnosed in the USA[1]. CRC develops in the soft tissues of a patient's digestive system – often in the lining of the colon or rectum.
The devastating reach of CRC is global, with recent studies revealing that one in 24 men and one in 26 women, world-wide, will develop colorectal cancer during their lifetime. This recent ACS report casts a spotlight on an emerging and highly concerning fact — one in five people diagnosed with CRC are now under the age of 55. Even younger, generally healthy adults are being affected [2].
The American College of Surgeons calls rates of colorectal cancer "alarming" and highlights the "dramatic rise" in cases in young adults in their mid-20s to late 50s. They state that this surge "remains a perplexing medical mystery for clinicians," while positing that diet and lifestyle surely play important roles. They also provide more data regarding increasing rates:
According to a 2023 report released by the American Cancer Society, colorectal cancer cases among adults younger than 55 increased from 11% (1 in 10) in 1995 to 20% (1 in 5) in 2019.
Building on those findings, a 2024 study, also from the American Cancer Society, looked at 23.6 million Americans who were diagnosed with 34 types of cancer from 2000 to 2019. Investigators found the probability of developing 17 types of cancers, including colorectal cancer, increased for individuals during early adulthood and middle age. "Each successive generation born during the second half of the 20th century has had increased incidences of many common cancer types of heterogeneous etiologies compared with preceding generations in the USA," noted the study authors.
Yale Medicine has also advised adults as young as 20 to be aware of the warning signs of colorectal cancer, which include rectal bleeding, constipation, or any sudden changes in bowel movements. Yale Medicine states:
"We are seeing a clear uptick in colorectal cancer in younger generations," says Haddon Pantel, MD, a Yale Medicine colorectal surgeon.
At the same time, while colorectal cancer is still most frequently diagnosed in people over 65, incidence in that group is declining, and older people are less likely than people younger than 50 to be diagnosed with advanced disease.
In fact, according to a 2024 report from the ACS, colorectal cancer has moved up from being the fourth leading cause of cancer death in both men and women under age 50 two decades ago to first in men and second in women. (Breast cancer is the leading cause of death in women under 50.)
Yale Medicine also states that while "nobody knows for sure" why colorectal cancers are increasing in younger people, they provide some possible reasons:
Sedentary lifestyle, overweight and obesity, smoking, heavy alcohol use, low-fiber, high-fat diets or diets high in processed meats, and other environmental factors have all been associated with the disease. Family history of colorectal cancer or polyps, and conditions such as inflammatory bowel disease are also risk factors.
When someone is diagnosed with cancer at a young age, people also suspect genetics, but experts still haven't been able to use genetics to explain the surge. The most common genetic condition associated with colon cancer is Lynch Syndrome, which typically involves tumors on the right side of the colon. But that's not what's causing these cases. Yale doctors are seeing a lot of young people whose colorectal cancer seems to be happening sporadically, as opposed to being caused by a particular genetic syndrome, Dr. Reddy says.
While colorectal rates in younger people started rising before the beginning of the ongoing COVID-19 pandemic, they have continued their upward trajectory, so I'm going to posit that in addition to all of the factors discussed above, we also need to start considering the impact that repeated COVID-19 infections are having on increasing rates of all cancers, including colorectal cancers. With the giant caveat that I'm not a doctor (well, at least not the medical kind), I *have* been closely following COVID-19 news, so I know that more and more research is pointing to COVID-19 as being oncogenic.
For example, in a comprehensive review of the literature published last year in Springer Nature's peer-reviewed Cureus Journal of Medical Science, the authors conclude that, "COVID-19 may initiate carcinogenesis or worsen existing cancer through immune suppression and chronic inflammation, as well as genetic and epigenetic changes it may cause." It's at least another factor to consider, and more reason to mask up, clean the air, and avoid repeated COVID-19 infections.
Stay safe and healthy out there, friends!
Read the full study abstract about ultramarathoning and colorectal cancer here.
Previously:
• Organizers unprepared as woman wins ultra marathon outright
• Marathon runner disqualified for chain-smoking during race
• Common cooking oils linked to rising cancer rates in young adults
• Chadwick Boseman, 1976–2020
• Take lots of dietary supplements? You may have increased cancer risk, says new meta-study
