Research links regular movement, from walking to strength training, with longer life and better health. But exercise comes in many forms and the body responds differently depending on intensity, duration and recovery.
A new study has put the spotlight on extreme endurance events, suggesting that long-distance trail running can temporarily damage red blood cells. Experts say the finding sounds alarming, but context matters.
Researchers analysed blood samples from a small group of endurance athletes after ultra-distance trail races. They found signs that extreme exertion damaged red blood cells in ways that accelerated the usual ageing process of those cells.
The study, published in Blood Red Cells and Iron, followed 23 runners who completed either a 40-kilometre trail race or a 171-kilometre ultramarathon. Compared with pre-race testing, post-race bloodwork showed clear signs of oxidative and inflammatory stress affecting red blood cells, obesity medicine and sports medicine specialist Dr Dayna McCarthy explains.
After the ultramarathon in particular, the body showed stronger inflammation. Red blood cells showed signs of oxidative stress, often described as chemical “wear and tear”, and the cells became slightly less flexible, cardiologist Dr Deepak Talreja adds.
Red blood cells carry oxygen around the body and help transport nutrients, which is why doctors use them as a marker for certain health issues. “That is normal aging at the cellular level,” says Dr Talreja, referring to the way red blood cells naturally wear down over time.
The key detail is that red blood cells are not designed to last forever.
Why the findings are not as scary as they sound
Red blood cells typically live for about 120 days. Everyday life damages them gradually, then the spleen and liver clear older cells as part of normal turnover. “That is normal aging at the cellular level,” Dr Talreja says.
In the runners’ case, the race appeared to speed up that cycle, but likely only temporarily. The study did not include long-term follow-up to assess whether these changes persisted or caused lasting harm.
There is also a built-in repair system. “Bone marrow constantly produces new red blood cells,” Dr Talreja explains. “Healthy athletes typically replace these cells quickly, and there is no evidence that this process causes systemic ageing of the person.”
When could it become a concern?
The main open question is frequency and recovery. If someone takes on extreme endurance events too often without enough rest, it may increase the chance of longer-term strain.
Dr McCarthy notes the blood markers seen after ultra events can resemble patterns seen in severe infection and systemic inflammation. That does not mean a race causes the same level of harm, but it raises questions about cumulative stress if the body does not have time to fully recover.
Over time, red blood cells that do not function well could add strain to the vascular system, affect blood flow and contribute to low-grade inflammation, which can influence ageing and cardiovascular risk. Researchers still need more data to confirm whether those long-term effects occur in real-world endurance athletes.
Why cardio remains good for health and longevity
The study findings do not cancel out the wider evidence in favour of regular cardiovascular exercise. “Regular running and higher cardiorespiratory fitness are associated with lower all-cause and cardiovascular mortality,” explains Dr McCarthy. She adds that moderate to moderately high volumes tend to deliver the biggest benefits, and any risk from very extreme amounts, if it exists, appears small.
“Cardiorespiratory fitness is one of the strongest predictors of survival we have. Modest, consistent cardio—such as brisk walking, moderate intensity running, or cycling—delivers most of the longevity benefit,” she says.
The bottom line
“Extreme, single bout, ultra-endurance running acutely pushes red blood cells and the immune and metabolic systems into a state that looks like accelerated red blood cell ageing with significant oxidative and inflammatory stress,” says Dr McCarthy. For most healthy, well-prepared athletes, this is likely a short-term stress response, followed by recovery with adequate rest, hydration and nourishment.
Dr Talreja adds that strong evidence links moderate to high levels of aerobic fitness with longer life expectancy. Even endurance athletes who race often tend to show more favourable cardiovascular patterns than people who are mostly sedentary.
The most practical takeaway is to match training to recovery. Extreme events place real demands on the body, so preparation, fuelling and rest matter. If you have a heart condition, a history of anaemia, unexplained fatigue or symptoms such as chest pain, dizziness or palpitations, speak with a doctor before pushing intensity or distance.
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