Summary: New research from the University of the Basque Country shows that running a marathon can cause a temporary reduction in brain myelin—the fatty, lipid-rich insulation that surrounds nerve fibers and supports efficient neural signaling. The decrease in myelin was observed in brain regions involved in motor coordination, sensory processing and emotional integration, and appears to reflect the use of myelin lipids as an emergency energy reserve when the body’s primary fuels are exhausted during extreme endurance exercise.
Importantly, the study reports that the reduction is reversible: myelin levels begin to rebound within weeks and return to baseline within two months after the race. These findings suggest a previously underappreciated role for myelin in brain energy metabolism and may offer clues relevant to understanding and treating demyelinating conditions.
Key facts
- Temporary myelin reduction: Marathon running is associated with a measurable decline in myelin content in white-matter regions linked to motor and sensory functions.
- Full recovery: Myelin levels substantially recover within two weeks and return to pre-race values by two months.
- Metabolic role: The data suggest myelin lipids may be mobilized as an alternate brain energy source during prolonged, intense exercise.
Source: University of the Basque Country
Endurance exercise mobilizes the body’s energy reserves.
During long bouts of exercise such as marathon running, the body first relies on carbohydrates like muscle glycogen for fuel and then increasingly switches to fat stores once glycogen is depleted. Myelin, the multilayered lipid-rich sheath that insulates axons, is mainly composed of lipids, and prior animal studies have suggested these lipids can serve as an emergency energy source under severe metabolic stress.
A collaborative team from UPV/EHU, CIC biomaGUNE and IIS Biobizkaia used magnetic resonance imaging (MRI) to investigate how marathon running affects myelin content in humans. The study examined ten marathon runners (eight men and two women) with brain scans taken before the race and again 48 hours after completing the 42-kilometre event. Follow-up scans were acquired for two participants at two weeks and for six participants at two months post-race.
Using the myelin water fraction—a commonly used MRI surrogate for myelin content—the researchers identified a consistent reduction in myelin signal across 12 white-matter regions involved in motor coordination, sensory perception and emotional integration. According to the authors, these regional declines likely reflect mobilization of myelin lipids when other energy sources are low during prolonged exertion.
Two weeks after the marathon the myelin signal had increased substantially, though it had not yet fully returned to baseline. By two months post-race the myelin measurements were indistinguishable from the pre-race values, indicating a full and reversible recovery of myelin content following extreme endurance exercise.
Myelin as a brain energy reserve
The investigators conclude that myelin can function as an auxiliary energy depot in humans under conditions of severe metabolic demand, mirroring observations from rodent studies. They note that larger trials are required to confirm these results, to define how exercise intensity and duration influence myelin dynamics, and to determine whether transient changes in myelin have measurable effects on neurophysiological or cognitive performance.
The study highlights that most brain myelin remains unaffected, and the researchers emphasize that marathon running should not be considered harmful to the brain. On the contrary, the temporary use and subsequent replenishment of myelin lipids may stimulate adaptive metabolic processes that are beneficial to neural health.
These results broaden our understanding of brain energy metabolism and suggest potential avenues for research into demyelinating disorders. Understanding the mechanisms behind the rapid recovery of myelin after endurance stress could offer new insights for therapies aimed at promoting remyelination in diseases such as multiple sclerosis, where loss of myelin contributes to structural damage and neurodegeneration.
About this myelin and exercise research news
Author: Encarni Miguel
Source: University of the Basque Country
Contact: Encarni Miguel – University of the Basque Country
Image: The image is credited to Neuroscience News
Original Research: Closed access.
“Reversible reduction in brain myelin content upon marathon running” by Carlos Matute et al. Nature Metabolism
Abstract
Reversible reduction in brain myelin content upon marathon running
Using magnetic resonance imaging, this study investigates the effects of marathon running on brain structure in humans. We find that the myelin water fraction—a proxy for myelin content—decreases substantially in specific regions involved in motor coordination and sensory and emotional integration immediately after marathon running, but recovers within two months. These observations indicate that severe exercise can temporarily and reversibly reduce brain myelin content, consistent with animal evidence that myelin lipids may serve as glial energy reserves during extreme metabolic demand.