- Scientists link high-intensity, long-distance cardio (like marathon running) to red blood cell damage in a recent study.
- Researchers looked at the state of runners’ red blood cells before and after a trail race and ultramarathon.
- The cells showed evidence of oxidative stress and damage. Experts explain the health implications.
Research shows that anything from walking to strength training may add years to your life, underlying the importance of exercise. But there are so many different ways to get your blood pumping, and not all of them have the same impact on your body. Now, scientists say that a specific type of intense exercise, long-distance trail running, damages red blood cells. But experts say there’s more to it.
Meet the Experts: Dayna McCarthy, D.O., a double board-certified obesity medicine and sports and interventional spine medicine specialist at Parsley Health; and Deepak Talreja, M.D., clinical chief of cardiology at Sentara Health.
Researchers looked at the red blood cell counts of a small number of ultra-marathon runners post-race and found that the bouts of extreme exercise caused damage that accelerated aging of the cells. Red blood cells work to deliver oxygen to the lungs and carry nutrients throughout the body, so you could say they’re pretty important to health. Which is why they’re examined as markers for conditions like anemia, malnutrition, and leukemia, per the National Cancer Institute.
So, does this mean completing a marathon (or ultra-marathon) does more harm than good? Not quite. The study, published in Blood Red Cells and Iron, consisted of 23 runners who completed a 40-kilometer trail race and a 171-kilometer ultramarathon, blood tests (compared to pre-race tests) showed clear signs of oxidative and inflammatory damage to red blood cells, explains Dayna McCarthy, D.O., a double board-certified obesity medicine and sports and interventional spine medicine specialist at Parsley Health. After the ultramarathon, especially, the body showed strong inflammation, red blood cells showed signs of oxidative stress (a.k.a. chemical wear and tear), and the cells became slightly less flexible, adds Deepak Talreja, M.D., clinical chief of cardiology at Sentara Health.
Red blood cells work to deliver oxygen to the lungs and carry nutrients throughout the body, so you could say they’re pretty important to health. Which is why they’re examined as markers for conditions like anemia, malnutrition, and leukemia, per the National Cancer Institute.
The study results may sound jarring at first, but it’s important to note that red blood cells only live about 120 days. Daily life damages them over time, and they are then removed by the spleen and liver. “That is normal aging at the cellular level,” says Dr. Talreja.
In the runners’ cases, racing accelerated that life cycle, only temporarily. And researchers didn’t follow up to examine whether or not the isolated events caused long-term damage. Plus: “Bone marrow constantly produces new red blood cells,” explains Dr. Talreja. “Healthy athletes typically replace these cells quickly, and there is no evidence that this process causes systemic aging of the person.”
Theoretically, if the runners engaged in intense marathons too often, there may be more risk of long-term damage because the blood markers were similar to those seen in severe infections and systemic inflammatory states, says Dr. McCarthy. But more research is needed, and scientists have yet to prove this. Red blood cells that don’t work well over time may lead to stress on the vascular system, negatively impact blood flow, and lead to to low-grade inflammation, which impact aging and cardiovascular disease.
Why cardio remains good for health and longevity
“Regular running and higher cardiorespiratory fitness are associated with lower all‑cause and cardiovascular mortality,” explains Dr. McCarthy. Moderate to moderately high volumes lead to the most benefits, and the risk from very extreme amounts, if present at all, is small, she says.
“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 aging with significant oxidative and inflammatory stress,” says Dr. McCarthy. For most healthy, well-prepared athletes, this likely shows a short-term stress, followed by making it up (with nourishment and hydration).
Hefty data shows that moderate-to-high levels of aerobic fitness have a strong association with longer life expectancy, adds Dr. Talreja. Even endurance athletes who race often generally show positive cardiovascular patterns compared with people who lead more sedentary lifestyles.
Experts advise exercising caution in high-stress and high-impact physical activity. But more research is needed before making any definitive decisions. As always, consult your physician before changing up your routine.
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