They’re running themselves ragged — and possibly fast-tracking Father Time.
Ultramarathons are surging in popularity, with more than 100,000 North Americans racing beyond 26.2 miles last year, nearly triple the 35,000 who did so in 2020.
But before you lace up your sneakers, here’s the catch: New research suggests that people who tackle these extreme endurance events may be prematurely aging a vital part of their bodies, potentially affecting how it functions.
In the past, studies have shown that ultramarathon runners often experience a breakdown of normal red blood cells during races, which can sometimes lead to anemia and other health issues, but the causes have remained unclear.
To investigate, scientists at the University of Colorado Anschutz collected blood samples from 23 runners immediately before and after a 25-mile race and a 106-mile race.
They analyzed the samples for thousands of proteins, lipids, metabolites and trace elements in both their plasma and red blood cells.
They found that the athletes’ red blood cells became less flexible after a long race — a crucial change since these cells must be able to bend in order to pass through tiny vessels and transport oxygen, nutrients and waste throughout the body.
The runners’ red blood cells showed two types of damage: physical and molecular.
The researchers suspect the physical damage comes from the pressure of blood surging through the body during long runs.
The molecular damage, they say, likely results from inflammation and oxidative stress — a condition in which the body has low levels of antioxidants, leaving cells vulnerable to damage that can affect DNA and other vital components.
“Participating in events like these can cause general inflammation in the body and damage red blood cells,” Dr. Travis Nemkov, the study’s lead author and associate professor of biochemistry at CU Anschutz, said in a statement.
“Based on these data, we don’t have guidance as to whether people should or should not participate in these types of events,” he continued, “what we can say is, when they do, that persistent stress is damaging the most abundant cell in the body.”
These patterns of damage — essentially accelerating the aging and breakdown of red blood cells — were clearly seen after 25-mile races and were amplified in athletes who ran 106-mile races.
The team suspects that longer races lead to greater red blood cell loss and more strain on the ones left in circulation.
“At some point between marathon and ultra-marathon distances, the damage really starts to take hold,” Nemkov said.
“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.”
The study had its limits. It included just 23 participants, lacked racial diversity and collected blood at only two points, leaving key questions about timing and long-term effects unanswered.
Even so, the researchers said future studies could use these findings to help athletes boost performance and reduce risks through personalized training, nutrition and recovery plans.
Beyond athletics, the team is exploring how what they’ve learned from runners’ blood could help improve the storage and preservation of donated blood.
Across the country, hospitals need more than 29,000 units of red blood cells every day for surgeries, cancer treatments, chronic illnesses and emergency trauma. But outside the body, these cells start to break down after a few weeks, becoming unusable for transfusions after six.
“Red blood cells are remarkably resilient, but they are also exquisitely sensitive to mechanical and oxidative stress,” Dr. Angelo D’Alessandro, professor at CU Anschutz and a member of the Hall of Fame of the Association for the Advancement of Blood and Biotherapies.
“This study shows that extreme endurance exercise pushes red blood cells toward accelerated aging through mechanisms that mirror what we observe during blood storage,” he explained.
Since no artificial substitute exists, hospitals rely entirely on volunteer donors, and extending blood’s shelf life could potentially help ease chronic shortages.
Looking ahead, the researchers are planning larger studies with more participants and additional post-race measurements. They also aim to explore ways to extend the shelf life of stored blood.
