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Ultra-Marathons Harm Red Blood Cells, Study Reveals

2/26/2026

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Story summary
  • A study published in Blood Red Cells & Iron finds ultra-marathon running damages red blood cells and reduces their flexibility.
  • Researchers analyzed blood samples from 23 elite runners before and after two races: 40-kilometer event and 171-kilometer event.
  • They found that longer races caused greater cellular stress and accelerated aging of red blood cells.
  • The study does not give participation guidance, notes health implications, and calls for future research to improve blood storage and training.