Ultramarathon Running Damages Red Blood Cells, Accelerates Aging

Ultra-marathon running can damage red blood cells in ways that accelerate their aging and breakdown, potentially interfering with how they deliver oxygen throughout the body, according to new research. A study published in the journal Blood: Red Cells & Iron found that extreme endurance events alter red blood cells, making them less flexible and more prone to breakdown, which can potentially lead to anemia.

Running extreme distances may do more than exhaust muscles. Researchers found that after prolonged races, red blood cells become less flexible. Because these cells must bend to pass through tiny blood vessels while delivering oxygen and removing waste, reduced flexibility may limit their efficiency. The team created the most detailed molecular profile to date showing how endurance races alter red blood cells.

To examine these effects, researchers measured indicators of red blood cell health before and after athletes competed in two demanding races: the Martigny-Combes à Chamonix race (40 kilometers or about 25 miles long) and the Ultra Trail de Mont Blanc race (171 kilometers or 106 miles long). The team collected blood samples from 23 runners immediately before and after their races. They analyzed thousands of proteins, lipids, metabolites, and trace elements in both plasma and red blood cells.

The results consistently showed signs of injury driven by both mechanical and molecular factors. Mechanical stress likely resulted from shifts in fluid pressure as blood circulates during intense running. Molecular damage appeared linked to inflammation and oxidative stress. Blood pressure changes, inflammation and oxidative stress all caused damage to red blood cells during long-distance running.

Evidence of accelerated aging and increased breakdown of red blood cells was visible after the 40 kilometer race and was even more pronounced among athletes who completed the 171 kilometer event. This pattern of damage was clearly seen after the 25-mile race and was amplified in the 106-mile race. Based on these findings, researchers suggest that longer races may lead to greater loss of red blood cells and more damage to those that remain in circulation.

"At some point between marathon and ultra-marathon distances, the damage really starts to take hold," said the study's lead author. "We've observed this damage happening, but we don't know how long it takes for the body to repair that damage, if that damage has a long-term impact, and whether that impact is good or bad."

As the length of a run increases, athletes can expect to lose more red blood cells and accumulate more damage to those cells remaining in circulation. However, researchers can't say how this depletion of red blood cells will affect athletes' short-term or long-term health.

"Based on these data, we don't have guidance as to whether people should or should not participate in these types of events," the lead researcher said. "What we can say is, when they do, that persistent stress is damaging the most abundant cell in the body."

The work may also have broader medical relevance. Stored blood used for transfusions begins to deteriorate after several weeks and must be discarded after six weeks under U.S. Food and Drug Administration regulations. Understanding how intense physical stress affects red blood cells could provide insight into improving blood storage practices.

"Red blood cells are remarkably resilient, but they are also exquisitely sensitive to mechanical and oxidative stress," said a study co-author. "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."

Researchers plan to repeat this study using more participants and additional blood samples taken during and after races.