Widespread drastic reduction in brain myelin content upon marathon running

Recent evidence suggests that myelin lipids may act as glial energy reserves when glucose is lacking, a hypothesis yet to be solidly proven. Hereby, we examined the effects of running a marathon on myelin content by MRI. Our findings show that marathon runners undergo widespread robust myelin decrease at completion of the effort. This reduction involves white and gray matter and includes primary motor and sensory cortical areas and pathways, as well as the entire corpus callosum and internal capsule. Notably, myelin levels partially recover within two weeks after the marathon. These results reveal that myelin use and replenishment is an unprecedented form of metabolic plasticity aimed at maintaining brain function during extreme conditions.