A small study of marathon runners found that their brains' energy demands increased after the race. (Image credit: anatoliy_gleb via Shutterstock)
Marathon running may seem like a great way to stay fit. However, it can cause significant harm to the body, potentially damaging the kidneys, causing stomach upset, increasing the risk of heart failure, and leading to musculoskeletal injuries. It’s worth remembering that the first marathon runner, the ancient Greek soldier Pheidippides, is said to have dropped dead immediately after reaching his goal.
New research shows that marathons also impact the brain, forcing it to use its own resources to restore the energy lost during running.
In a study published March 24 in the journal Nature Metabolism, scientists noted a decrease in an important biomarker of myelin, the fatty tissue that insulates the connections between neurons, in marathon runners immediately after the race. The study authors say this indicates that the brain uses myelin as an energy source in these extreme conditions.
Fortunately for long-distance runners, these effects appear to be reversible.
When the body runs out of its primary energy source—glucose, or sugar—it turns to reserve sources, metabolizing fats as an alternative fuel source. The brain, in terms of metabolic activity, is more like a Humvee than a hatchback; this energy-hungry organ consumes 20 percent of the body’s energy, making it vulnerable when fuel sources run low.
Pedro Ramos Cabrera, a neuroscientist at CIC biomaGUNE, a nonprofit research institute in San Sebastian, Spain, and a co-author of the study, told Live Science that he and his colleagues wanted to identify the brain’s reserve energy sources. They suspected that fatty myelin might be the answer. Previous studies in rodents have suggested that fatty acids released when myelin breaks down may help neurons survive longer. However, it remains to be seen whether these preclinical findings will translate to humans.
“To prove this, we had to completely deplete all of the body's energy sources,” Cabrera told Live Science.
The team studied the brains of 10 runners 48 hours before their marathon, and then again two days, two weeks and two months after. They used MRI, which can detect water molecules trapped between layers of myelin.
Brain scans showed that two days after the race, MRI signals in 12 brain regions were reduced compared to pre-race levels – in some cases by up to 28%. However, changes in overall myelin levels in the brain were not statistically significant, suggesting that any changes were very localised and specific to specific areas.
“The areas where we saw more significant changes were in the motor circuits and the emotional control center of the brain,” Cabrera said, suggesting that this reflects the mental and physical effort the brain must make to cope with a marathon.
For all the runners worried about this cerebral cannibalism, there's some encouraging news: After two months, all of the runners' myelin levels had returned to baseline.
Klaus-Armin Nave, director of the Max Planck Institute for Interdisciplinary Sciences in Germany, was not involved in the study but has also studied how myelin stores energy using lab mice. Nave said the study’s findings are consistent with how neuroscientists think myelin maintains energy balance in the brain.
“Myelin is constantly being made and broken down,” he explained. “It’s like a bathtub where you’re constantly filling it with water and draining it at the same time.” He added that Cabrera’s work provides “very compelling evidence” that the brain’s metabolic demands increase after a marathon. As a result, the fuel stored
Sourse: www.livescience.com
