Can Extreme Endurance Running Damage Your Blood Cells?
Yes. A study of 23 trail runners found that a 40 km trail race and a 171 km ultramarathon both triggered systemic inflammation, and that long-distance trail running induces inflammation-associated protein, lipid, and purine oxidation in red blood cells. The cells became less deformable and showed signs of accelerated aging after the races.
Red blood cells are the tiny disc-shaped cells that carry oxygen from your lungs to every part of your body. They need to be flexible enough to squeeze through the smallest blood vessels. When these cells get damaged or stiff, they cannot do their job as well. This study looked at what happens to these cells when runners push their bodies to the extreme, and the findings raise important questions about how much exercise is too much.
Dr. Kumar’s Take
I find this study useful because it adds nuance to the conversation about exercise. Regular physical activity is one of the best things you can do for your health. But this research suggests there may be a point where extreme endurance events start working against the body rather than for it. The red blood cells here did not just look tired, they carried molecular lesions consistent with accelerated aging, and the damage tracked with the longer race rather than the shorter one. What I take from it clinically is the mechanism: the authors link systemic inflammation to oxidative injury inside the cell, then to impaired deformability, then to clearance of those cells by the spleen. That is a chain, not a single insult. This does not mean you should avoid running. It means that if you are training for ultra-endurance events, you need to take recovery and nutrition seriously. The body has limits, and respecting those limits is part of being a smart athlete.
How Ultramarathons Affect Red Blood Cells
Researchers collected blood samples from 23 endurance-trained runners before and immediately after two different trail races. Eleven runners (5 women, 6 men, aged 35.7 ± 8.6 years) completed the 40 km Martigny-Combe to Chamonix race, which has 2300 m of elevation gain. Twelve runners (4 women, 8 men, aged 38 ± 6.4 years) completed the 171 km Ultra-Trail du Mont-Blanc, with 10 000 m of elevation gain. The two groups were compared against their own prerace samples, and the researchers profiled proteins, lipids, metabolites, and trace elements in both plasma and red blood cells.
Both races produced systemic inflammation. The 171 km race stood apart. It produced marked increases in interleukin-6 and kynurenine, induction of acute-phase proteins including C-reactive protein and serum amyloid A, and extensive lipid remodeling. Inside the red blood cells after the ultramarathon, the researchers found hydroxylated acylcarnitines, the oxidized linoleate derivative 13(S)-HODE, and kynurenine, along with rises in biliverdin and bilirubin. After the 40 km race, red blood cells accumulated acylcarnitines and fatty acids while pantothenate fell, a pattern the authors read as increased flux through coenzyme A dependent repair pathways.
The protein damage was not random. Proteomics showed methionine oxidation concentrated in antioxidant enzymes, metabolic proteins, and proteasome components, and that oxidation correlated with impaired deformability on rheological testing. Elevated copper was an additional correlate of reduced red blood cell mechanics. Purine salvage and carboxylate metabolism shifted in a way the authors describe as redox-sensitive rerouting of energy pathways. Together these changes made the cells behave older than they should have.
What This Means for Runners
These findings do not mean that running is bad for you. The study did not test moderate exercise against sedentary living, and it did not follow anyone beyond the finish line. What it does show is that the longer event produced the deeper molecular injury, in the same athletes measured against themselves.
Notably, the researchers found minimal signatures of intravascular hemolysis, meaning the cells were not simply bursting inside the blood vessels from the pounding of footstrike. Instead, plasma bilirubin and hypoxanthine rose, which is consistent with damaged cells being pulled out of circulation by the spleen. The authors conclude that ultrarunning accelerates red blood cell aging through inflammatory and oxidative pathways beyond mechanical trauma. That reframes an old assumption in the sport.
Performance data pointed the same direction. Runners averaged 6.1 km/h in the 40 km race versus 4.4 km/h in the 171 km race. A linear mixed model found 51 plasma molecules significantly associated with speed, spanning multiple lipid classes and tryptophan catabolites, while only red blood cell ADP correlated with pace. Plasma captured the moment-to-moment adjustments to workload. The red blood cells recorded the integrated oxidative and metabolic burden of the whole race.
Important Limitations
This was a small study with 23 participants split between the two races. The researchers measured blood immediately after each race, so the duration of the damage and the extent of recovery are outside what this design can show. There was no non-running comparison group. Individual variation in fitness, genetics, and nutrition could influence how much damage each runner sustained. The authors also note that their high-throughput method does not resolve biliverdin isomers. Larger studies with follow-up measurements after races would help.
Practical Takeaways
- If you train for ultramarathons, prioritize recovery days and allow your body enough time between extreme events for your blood cells and other tissues to repair.
- Pay attention to nutrition during heavy training blocks, since oxidative injury to proteins and lipids inside the red blood cell was a central finding here.
- Work with a sports medicine doctor to monitor your blood health if you race ultra-endurance events regularly, since the damage found in this study may not produce symptoms but was measurable at the molecular level.
- Remember that the deepest changes in this study came from the 171 km race, not the 40 km one, and that the researchers frame these findings as a foundation for actionable biomarkers rather than a reason to stop running.
Related Studies and Research
- Small Changes in Sleep, Exercise, and Diet Linked to 9 Extra Years of Life explores how balanced lifestyle habits deliver powerful longevity benefits without extreme effort.
- Mitochondria in Oxidative Stress, Inflammation and Aging explains how oxidative damage at the cellular level drives aging, a core mechanism in this ultramarathon study.
- Why Do Cancer Cells Choose Inefficient Energy Production? looks at how disrupted energy metabolism affects cells, similar to the purine pathway changes seen in damaged red blood cells.
- Long-Term Oxygen Treatment Trial (LOTT) and Health Benefits examines how oxygen delivery affects health outcomes, which connects to red blood cell function and flexibility.
FAQs
How long does it take for red blood cells to recover after an ultramarathon?
This study sampled runners before and immediately after their races, so recovery time is beyond what the data can answer. The researchers did describe the mechanism by which damaged cells leave circulation: plasma bilirubin and hypoxanthine rose without much sign of intravascular hemolysis, consistent with the spleen clearing damaged cells. The open question is whether repeated ultra-endurance events cause cumulative damage that outpaces the body’s ability to replace those cells. Athletes who race frequently should discuss blood monitoring with their doctor.
Is this type of red blood cell damage unique to ultramarathons, or does it happen with shorter runs too?
This study gives a direct comparison between two distances. Both the 40 km and the 171 km races elicited systemic inflammation, so the shorter trail race was not benign. But the 171 km ultramarathon was distinguished by marked interleukin-6 and kynurenine increases, acute-phase protein induction, and profound lipid remodeling, and its red blood cells carried oxidized lipid species and hydroxylated acylcarnitines that the 40 km samples did not. The 40 km runners showed a different signature: acylcarnitine and fatty acid accumulation with falling pantothenate, which the authors interpret as repair pathway activity. That contrast points to duration as the driver.
Should recreational runners worry about red blood cell damage?
This study enrolled endurance-trained athletes competing in mountain trail races, so it does not speak to recreational running. The authors position their results as translational insight into oxidative lesions, noting that the damage red blood cells accrue during ultrarunning mirrors what happens to stored blood under blood bank conditions. That is a statement about extreme physiological stress, not about a weekend 5K. If you are training for a mountain ultra, the findings are relevant to you. If you are running a few times a week, they are not the study that should change your plans.
Bottom Line
This study of 23 trail runners, 11 racing 40 km and 12 racing 171 km, shows that long-distance trail running accelerates red blood cell aging through inflammation and oxidation rather than mechanical trauma alone. Methionine oxidation hit antioxidant enzymes, metabolic proteins, and proteasome components, and that oxidation correlated with impaired deformability. Elevated copper tracked with reduced cell mechanics. Rising plasma bilirubin and hypoxanthine, without much intravascular hemolysis, point to the spleen removing the damaged cells. The 171 km race carried the heavier molecular burden. For athletes who love going the distance, the message is to train smart, recover well, and give your body the nutrition and rest it needs to repair.
