Running a marathon is a remarkable feat that challenges not only the body but also the brain. While the physical demands of covering 42.195 kilometers are well-known, recent scientific research has shed light on how such endurance activities temporarily affect the brain’s structure, particularly the myelin sheath.

Understanding Myelin: The Brain’s Insulator

Myelin is a fatty substance that envelops nerve fibers, acting as an insulator to facilitate the rapid transmission of electrical signals within the nervous system. Comprising about 70–80% lipids, myelin is crucial for efficient neural communication, impacting everything from motor coordination to cognitive functions.

The Study: Marathon Running and Myelin Reduction

A study published in Nature Metabolism investigated the effects of marathon running on brain myelin content. Researchers conducted magnetic resonance imaging (MRI) scans on ten marathon runners, aged 45 to 73, at multiple intervals: 24–48 hours before the race, 24–48 hours after, two weeks later, and two months post-race.

The findings revealed a significant reduction in the myelin water fraction (MWF)—a surrogate marker for myelin content—in specific brain regions shortly after the marathon. Notably, areas involved in motor coordination and sensory and emotional integration exhibited the most pronounced decreases. However, these reductions were transient, with myelin levels returning to baseline within two months post-race.

Metabolic Myelin Plasticity: The Brain’s Adaptive Mechanism

The study introduced the concept of “metabolic myelin plasticity,” suggesting that during extreme endurance activities like marathons, the brain may utilize myelin lipids as an alternative energy source when glucose levels are depleted. This adaptive mechanism indicates that myelin could serve as an energy reserve under metabolic stress, highlighting the brain’s remarkable flexibility in maintaining function during prolonged physical exertion.

Implications for Cognitive Health

Importantly, the temporary myelin depletion observed does not appear to have adverse long-term effects. On the contrary, the body’s ability to restore myelin levels suggests a resilience that may even contribute to cognitive health benefits associated with regular endurance exercise. Studies have linked consistent aerobic activity with improved memory, enhanced focus, and a reduced risk of neurodegenerative diseases.

Conclusion: The Brain’s Resilience in Endurance Activities

While marathon running induces a short-term reduction in brain myelin, this effect is reversible and may reflect the brain’s adaptability to energy demands during prolonged physical exertion. These findings underscore the importance of understanding the brain’s dynamic responses to extreme physical challenges and open avenues for further research into the interplay between endurance exercise and neural health.

References:

• Ramos-Cabrer, P., et al. (2025). Reversible reduction in brain myelin content upon marathon running. Nature Metabolism. Link
• Biever, C. (2025). How marathons change runners’ brains: scans point to surprise energy source. Nature. Link
• Millard, E. (2025). Running a Marathon Has Pretty Big Effects on the Brain, New Research Says. Runner’s World. Link
• Mackenzie, R. J. (2025). Your brain starts eating itself during a marathon, study finds. Live Science. Link
• Lomte, T. S. (2025). Marathon running temporarily reduces brain myelin levels. News-Medical. Link

Note: This article is intended for informational purposes and should not replace professional medical advice. Always consult with healthcare professionals before starting any new exercise regimen.