Extreme endurance running, specifically ultramarathons, appears to cause faster aging of red blood cells than shorter races. New research indicates that pushing the body to its absolute limits over long distances induces significant cellular damage. While exercise is vital for health, this study suggests a threshold where intensity may become detrimental at a biological level.
How Ultramarathons Stress Red Blood Cells
Researchers at the University of Colorado Anschutz analyzed blood samples from ultramarathon runners (170 km) and shorter-distance trail racers (40 km). Both groups experienced increased damage from reactive oxygen species—molecules that naturally accumulate as cells age. However, the ultramarathon group showed substantially more damage.
According to Angelo D’Alessandro, one of the lead researchers, “The blood after an ultramarathon looks like the blood of somebody who’s just been hit by a car.” This means red blood cells accumulate damage faster and age more quickly. The study also found that the long-distance runners’ cells shifted toward a spherical shape, making them less efficient at oxygen delivery and more likely to be filtered out by the spleen.
Why This Matters
Red blood cells transport oxygen throughout the body. Accelerated aging of these cells means the body must work harder to maintain oxygen levels, potentially leading to temporary immune suppression, anemia, and other health complications. The study does not show long-term harm, but it raises questions about the cumulative effects of repeated ultramarathons.
The Science Behind the Stress
The increased stress on red blood cells is likely due to the combination of inflammation and forceful circulation during extreme exertion. The body responds to intense exercise by increasing oxygen demand, which leads to higher levels of reactive oxygen species and cellular damage.
While the 10% drop in red blood cell numbers observed in ultramarathon runners is unlikely to cause immediate anemia, it underscores the significant physiological toll of these races. The researchers are now studying how long these effects last and whether they influence performance.
The findings suggest that the body may be signaling a need for increased resilience to endurance running, but it remains unclear if this damage is ultimately beneficial or detrimental.
Further research is needed to determine whether repeated ultramarathons lead to long-term health consequences. For now, runners should be aware that these events place extreme stress on the body, especially at the cellular level.
