Study Suggests

A groundbreaking study finds that marathon running can temporarily reduce myelin levels in the brain, suggesting that under extreme energy demands, the brain may utilize its own fat stores for fuel.

Marathon Running and Brain Myelin: Understanding the Temporary Depletion

Emerging research indicates that marathon running can cause a temporary decrease in brain myelin content. This phenomenon suggests that during extreme endurance activities, the brain may utilize its own myelin—a fatty substance insulating nerve fibers—as an alternative energy source when traditional fuels are exhausted.

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The Study: Investigating Myelin Changes Post-Marathon

A study published in Nature Metabolism involved MRI scans of ten marathon runners (eight men and two women) aged between 45 and 73. Scans were performed 24 and 48 hours before, and 24 and 48 hours after completing a marathon.Additional scans were conducted two weeks and two months post-race for some participants.

Findings revealed a significant decrease in the myelin water fraction—a proxy for myelin content—in specific brain regions associated with motor coordination and sensory processing, such as the corticospinal tract and the corpus callosum. Notably, myelin levels returned to baseline within two months, indicating the changes are reversible.

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Understanding Myelin and Its Role

Myelin is a lipid-rich substance that forms a sheath around the axons of neurons, facilitating rapid electrical signal transmission. It constitutes approximately 40% of the brain’s white matter. Under normal conditions, the brain relies on glucose for energy. However, during prolonged endurance exercise, when glucose and glycogen stores are depleted, the body shifts to alternative energy sources.

This study suggests that in the absence of sufficient glucose, the brain may metabolize myelin lipids to meet its energy demands. This adaptive mechanism underscores the brain’s metabolic flexibility but also raises questions about the implications of repeated myelin depletion.

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Implications for Brain Health and Disease

While the temporary reduction in myelin appears to be a reversible adaptation to extreme energy demands, the long-term effects of repeated myelin depletion are not yet fully understood. Understanding how the brain restores myelin could have implications for treating demyelinating diseases such as multiple sclerosis, where myelin repair is a key therapeutic goal.

Further research is needed to explore the potential cognitive and neurological impacts of recurrent myelin depletion in endurance athletes and to determine whether this adaptation has any long-term consequences.

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Recommendations for Endurance Athletes

To mitigate potential negative effects on brain myelin during prolonged endurance activities:

• Adequate Nutrition: Ensure sufficient carbohydrate intake before and during endurance events to maintain glucose availability.
• Training Adaptations: Incorporate training strategies that enhance the body’s ability to utilize fats efficiently, potentially reducing the reliance on myelin lipids.
• Recovery: Allow adequate recovery time post-race to facilitate myelin restoration.