Ultramarathons: Study Reveals Damage to Red Blood Cells & Potential Health Risks
Extreme endurance running may be silently damaging red blood cells, potentially accelerating the aging process and impacting the body’s ability to efficiently transport oxygen, according to a new study published in the American Society of Hematology’s journal, Blood Red Cells & Iron. The research, released February 18, 2026, adds to a growing body of evidence suggesting that ultra-intense exercise can sometimes be detrimental to overall health.
Researchers at the University of Colorado Anschutz Medical Campus examined the effects of prolonged exertion on athletes participating in the Martigny-Combes à Chamonix race (40 kilometers) and the Ultra Trail de Mont Blanc (171 kilometers). Blood samples were collected immediately before and after the races, revealing that red blood cells became less flexible following both events. This reduced flexibility could hinder their ability to navigate the body’s smallest blood vessels, potentially diminishing oxygen delivery and waste removal.
“Participating in events like these can cause general inflammation in the body and damage red blood cells,” said Travis Nemkov, PhD, associate professor in the department of biochemistry and molecular genetics at the University of Colorado Anschutz, and lead author of the study. “Based on these data, we don’t have guidance as to whether people should or should not participate in these types of events; what we can say is, when they do, that persistent stress is damaging the most abundant cell in the body.”
The study involved analyzing thousands of proteins, lipids, metabolites, and trace elements in both plasma and red blood cells from 23 runners. Results indicated that the damage stemmed from both mechanical stress – likely caused by shifts in fluid pressure during intense running – and molecular damage linked to inflammation and oxidative stress. The longer the race, the more pronounced the signs of cellular stress became.
Previous research has established that ultramarathon runners often experience red blood cell breakdown during races, sometimes leading to anemia. However, the underlying mechanisms remained unclear until now. This new research provides the most detailed molecular map to date of how endurance races alter red blood cells, according to researchers.
Angelo D’Alessandro, PhD, professor at the University of Colorado Anschutz and a member of the Hall of Fame of the Association for the Advancement of Blood and Biotherapies, noted the parallels between the damage observed in athletes and the deterioration of stored blood. “Red blood cells are remarkably resilient, but they are too exquisitely sensitive to mechanical and oxidative stress,” he said. “This study shows that extreme endurance exercise pushes red blood cells toward accelerated aging through mechanisms that mirror what we observe during blood storage. Understanding these shared pathways gives us a unique opportunity to learn how to better protect blood cell function both in athletes and in transfusion medicine.”
The findings could have implications for both athletic training and blood storage practices. Researchers suggest that a deeper understanding of these cellular changes could inform personalized strategies for nutrition, recovery, and training to minimize harm. Stored blood, which currently has a limited shelf life of six weeks under U.S. Food and Drug Administration regulations, might benefit from strategies developed based on this research.
The study’s authors acknowledge limitations, including a small sample size and a lack of racial diversity among participants. They also noted that blood samples were collected at only two time points. Future research will focus on expanding the participant pool, collecting more frequent blood samples, and conducting more detailed measurements to assess the long-term effects of ultra-endurance running on red blood cell health. They also plan to investigate methods for extending the shelf life of stored blood.