Ultramarathons May Accelerate Red Blood Cell Aging, Study Finds

As running has become a cultural phenomenon, participation in events ranging from 10km races to half marathons, full marathons (42.195km), and ultramarathons is rapidly growing.

While running is recognized as an effective health hobby for strengthening cardiopulmonary endurance and relieving stress, research on the effects of extreme endurance exercise on the body is ongoing. A new study has found signs that ultramarathons may accelerate premature aging of red blood cells.

A research team led by Travis Nemkov, associate professor of biochemistry at the University of Colorado Anschutz Medical Campus, collected blood samples from 23 runners before and after 40km and 171km races to examine the effects of ultramarathons on red blood cells. The team tracked physiological changes by analyzing thousands of indicators including proteins, lipids, metabolites, and trace elements in plasma and red blood cells. Both races induced systemic inflammatory responses, but markers were significantly more elevated after the 171km ultramarathon.

Notably, reduced red blood cell flexibility stood out as a key finding. Red blood cells must freely change shape to pass through narrow capillaries; when this ability declines, oxygen and nutrient delivery and waste removal may be impaired. The researchers identified two types of damage following long-distance running. The first is physical damage—prolonged running increases mechanical stress from blood flow, straining cell membranes. The second is molecular damage. As inflammation and oxidative stress intensified, lipid and protein oxidation occurred, and antioxidant enzymes were damaged. The researchers said these changes resemble accelerated aging at the cellular level.

These changes appeared after the 40km race but were far more pronounced after the 171km event. "There may be a point somewhere between a marathon and an ultramarathon where red blood cell damage really starts to kick in," Nemkov said. However, he added, "Current data does not provide grounds to recommend or restrict ultramarathon participation. Further research on long-term effects and recovery periods is needed."

The study has limitations, with only 23 participants and blood samples taken at just two time points. How quickly damage recovers and whether cumulative effects occur with repeated participation remain unknown. The researchers noted the findings could have implications beyond sports medicine for transfusion medicine. Red blood cells undergo oxidation and structural changes during storage outside the body, and the changes observed in ultramarathons share similarities with this process, potentially offering clues for improving blood storage technology. The study was published in the journal Blood Red Cells & Iron.