When it comes to running, it turns out, more isn’t necessarily always better, as extreme distances could be prematurely aging your body.
Researchers at the University of Colorado Anschutz analyzed blood samples from 23 athletes immediately before and after they completed a 24-mile (40km) marathon or a grueling 108-mile (174km) ultra-marathon.
Before the races, participants had healthy red blood cells — vital for delivering oxygen to cells — that were flexible and easily passed through tiny blood vessels.
But after they crossed the finish line, these cells were more rigid, impairing circulation, and showed signs of inflammation and physical stress.
Overall, those who ran the ultramarathon had significantly more damage to their red blood cells.
Researchers said the deterioration of the cells closely matched what they would expect to record in an aging body, where the cells also become more rigid and less able to carry oxygen.
Dr Angelo D’Alessandro, a biologist and senior author of the study, said: ‘Red blood cells are remarkably resilient, but they are also exquisitely sensitive to mechanical and oxidative stress.
‘This study shows that extreme endurance exercise pushes red blood cells toward accelerated aging through mechanisms that mirror what we observe during blood storage.’
Researchers at the University of Colorado Anschutz analyzed the blood samples from 23 runners before and after they completed a marathon or an ultramarathon (stock photo)
Researchers found that the runners suffered damage to their red blood cells that mirrored changes normally seen with aging (stock image)
He continued: ‘Understanding these shared pathways gives us a unique opportunity to learn how to better protect blood cell function both in athletes and in transfusion medicine.’
Researchers said that the damage to the cells recorded during running was likely the result of inflammation and running-induced variations in fluid pressure as the cells circulated through the body.
They added that their results did not suggest that people should stop running altogether, but that they showed running these marathons led to red blood cell damage.
Participants only had their blood tested immediately after the race, meaning it was not clear whether the damage to the cells was permanent.
In the study, published in the journal Blood Red Cells and Iron, the team tested thousands of biomarkers in the blood.
Overall, 11 participants completed the Martigny-Combe a Chamonix, a 25-mile route from Switzerland to France, run by about 1,000 athletes every August.
Another 12 completed the Ultra-Trail du Mont-Blanc, a 108-mile route into France, Italy and Switzerland, considered one of the most ‘mythical and prestigious’ running races in the world. It takes place in August and is attended by about 10,000 runners yearly.
For comparison, both the New York City and London marathons are 26.2 miles (42km) long.
Shown above are runners in the 2024 New York City marathon, which is 26.2 miles (42km) long
Runners are shown above in the 2024 New York City marathon crossing the Verrazzano-Narrows Bridge
Participants in the study were 36 years old on average. Fourteen were men and nine were women. It was not clear exactly how much blood was extracted.
In the analysis of their blood, researchers tested thousands of biomarkers to track changes that occurred during the endurance race.
Dr Travis Nemkov, a biochemist who led the research, told Runners World: ‘At some point between marathon and ultramarathon distances, the damage really starts to take hold.
‘We’ve observed this damage happening, but we don’t know how long it takes for the body to repair that damage, if that damage has a long-term impact and whether that impact is good or bad.’
Based on their results, they warned that as the length of a run increases, athletes can expect to lose more blood cells and accumulate more damage to those remaining in circulation.
In aging, red blood cells accumulate damage, making them more rigid and leading to a decline.
This means they carry less oxygen and nutrients to tissue, reducing oxygenation and raising inflammation levels and cardiovascular stress, as the heart works harder to supply the body with the same nutrients.
Older red blood cells can also clump together, making the blood more viscous and hindering blood flow, raising the risk of a stroke or heart attack.
Studies suggest that this starts in a person’s 50s, before becoming more pronounced in their 60s.
Doctors urge people to exercise, and suggest running as a great way to boost the cardiovascular system and improve overall health and fitness.
But some physicians also raise concerns over ultra-marathon events, warning that completing these may raise the risk of complications such as heart attacks. Emerging research has also previously linked them to a higher risk of colon cancer.
An estimated 50 million people participate in jogging or running in the US every year, while 130,000 complete ultra-marathons every year.
