Researchers may have identified a potential connection between extreme endurance running and colorectal cancer, as nearly half of marathon and ultra-marathon participants have undergone screening.

Initial research assembled 100 long-distance runners aged 35-50 for colonoscopy, though these findings have not yet been peer-reviewed.

Close to 50% were found to have polyps (growths), with 15% diagnosed with advanced adenomas—growths that are likely to progress to cancer.

In contrast, recent studies indicate that only about 4.5 to 6 percent of adults in their late 40s from the general population have these advanced adenomas. However, it’s important to note that these studies included significantly larger sample sizes.

“I was quite concerned when I observed a group of ultra-marathon runners in their 30s diagnosed with stage 4, very advanced colorectal cancer,” said Dr. Timothy Cannon, who led the study at the Inova Schar Cancer Institute in Virginia. BBC Science Focus.

“They reported experiencing bleeding and convulsions post-race. At least one or two mentioned that they were told this was normal following their runs.”

Such symptoms can result from ischemic colitis, where blood flow is diverted from the colon to supply oxygen to the legs and other muscles during intense activity. This can lead to swelling and bleeding but typically resolves spontaneously.

Dr. Cannon speculated whether repeated cycles of damage and healing could create conditions conducive to cancer development.

“There is currently no evidence that ischemic colitis directly causes cancer,” he stated. “However, it’s not difficult to imagine the potential outcomes. When numerous cells die and regenerate chaotically, there are ample chances for DNA replication errors.”

Alternative explanations exist as well. Endurance athletes are known to possess distinct gut microbiota compared to non-runners, and they often consume considerable amounts of ultra-processed foods, such as bottled energy drinks.

Dr. Cannon’s team is preparing to compare the gut bacteria of runners with and without adenomas to that of non-runners.

The findings were presented at the American Society of Clinical Oncology’s annual meeting, yet researchers cautioned that these are merely preliminary results, necessitating further investigation. They also highlighted that the screening study lacked a control group of non-runners.

“This leans more toward hypothesis than definitive answers,” Cannon remarked.

“I definitely don’t want people to walk away thinking exercise is harmful because it is beneficial overall. The inquiry is whether high levels of exercise could elevate the risk of colon cancer—and I believe they might.”

Read more:

• Running slowly may be essential for a healthier, longer lifespan. Here’s why
• What are the limits of human endurance?
• The astonishing truth about how running can alter one’s perception of time

Source: www.sciencefocus.com