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This is your brain. This is your brain on marathons
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That old PSA line might hold some truth, according to a new study out of Spain
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Researchers at the Center for Cooperative Research in Biomaterials scanned the brains of 10 marathon runners before and after their races
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What they found was surprising. The brain's insulation, a fatty tissue called myelin
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appeared to shrink after the run. In some areas, levels dropped by nearly 30%
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That myelin helps brain cells communicate. It's like the coating on electrical wires, and it's made almost entirely of fat
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Under normal conditions, it's stable. But when the body runs out of its usual energy sources, like glucose
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the brain starts pulling energy from fat. And it turns out, in extreme cases, like a marathon, that includes fat in the brain itself
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The process is not permanent. Within two months, the runner's myelin levels had bounced back
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Researchers say this response highlights how the brain adapts under stress and may inform future studies on neurological health
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Scientists say the process appears harmless in healthy runners, but it could raise concerns for people with conditions like multiple sclerosis
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where myelin does not naturally regenerate. In those cases, even a temporary loss might not be easily repaired
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It is unclear how much strain extreme endurance puts on vulnerable brains
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But this study is a step toward finding out. The findings published in Nature Metabolism do not suggest marathons are dangerous for healthy people
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If anything, they show just how resilient the brain can be under stress
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So next time you lace up for 26.2 miles, remember, it's not just your legs doing the work
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