New research shows marathon running causes a temporary drop in brain myelin but experts say this process may actually sharpen your brain long-term. Here's why that's good news for runners.
We already know running is good for the body but what about the brain? A recent study has uncovered a surprising short-term effect marathons have on the brain, and while it might sound alarming at first, it could actually point to positive long-term benefits.
The study, published in Nature Metabolism, found that running a marathon causes a temporary drop in a substance called myelin, which plays a critical role in brain health.
But rather than being a cause for concern, researchers believe this change could be part of how endurance running helps keep the brain sharp over time.
Myelin is a fatty substance that wraps around nerve fibers in the brain and spinal cord. It’s vital for transmitting signals efficiently between nerve cells think of it like insulation on electrical wires.
About 40 percent of your brain’s white matter is made up of myelin, and it’s essential for coordination, learning, memory, and sensory processing.
It also helps convert glucose into energy for the brain. And during a marathon, that energy demand skyrockets.
Researchers from the University of the Basque Country in Spain used MRI scans to observe the brains of 10 runners (ages 45 to 73) before and after a marathon.
They scanned the participants 24 and 48 hours before the race, then again 24 and 48 hours after.
Two participants were also scanned two weeks later, and six were scanned again after two months.
The results showed a noticeable dip in something called myelin water fraction, a marker of how much myelin is present. This decline was temporary and that’s key.
The theory is all about energy. Just like your body uses stored carbohydrates (glycogen) during long efforts, your brain also needs fuel.
When it runs out of glucose, it may start tapping into the lipids from myelin as an energy source.
So while it may sound counterintuitive, burning some of that myelin might actually be the brain's way of adapting to stress.
And much like muscles after a tough workout myelin regenerates.
Not at all, say the researchers.
According to study co-author Carlos Matute, Ph.D., the temporary myelin dip might actually help your brain optimize its function. In fact, this regenerative cycle could strengthen the brain’s ability to handle energy demands and stress more efficiently.
“These changes are very subtle and completely reversible,” Matute said. “This is likely a good thing it exercises the brain’s metabolic machinery.”
Just as lifting weights causes minor muscle damage that leads to stronger muscles, marathon running might challenge and refresh the brain’s energy systems.
Interestingly, the study included runners who fueled with carbs during the race and those who didn’t.
At this early stage, there didn’t seem to be a major difference in myelin response between the two groups.
However, researchers believe future studies could shed more light on how nutrition affects brain recovery post-marathon.
It’s possible that better fueling especially carbohydrates might reduce how much myelin the brain needs to tap into, or help it bounce back faster.
Another variable that wasn’t examined in this particular study was race pace.
Could running faster and burning through fuel more quickly lead to greater myelin reduction? That’s another area the research team plans to explore.
Even with this temporary dip in myelin, the researchers are clear: marathon running is still overwhelmingly beneficial for the brain.
Not only is the myelin loss reversed quickly, but the brain might actually become stronger through this stress-recovery cycle.
And if you're wondering whether the researchers themselves believe in the power of running, consider this: they’re all runners and some, like Matute, have logged over a dozen marathons.
So while your legs might feel the burn after 26.2 miles, your brain is doing some important work of its own and getting better because of it.
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