Unusual Brain Shrinkage Observed in Long-Distance Runners

Each year, over a million people of all ages participate in marathons, reaping various health benefits from running. However, researchers caution that long-distance running may negatively impact the brain, with effects lasting up to a month after a race.

Scientists from Spain’s University of the Basque Country (UPV/EHU) have found a connection between marathon running and a significant decline in myelin, the protective sheath around nerve fibers (axons) in the brain. This insulation is essential for transmitting electrical signals in the brain and spinal cord, and its loss is associated with neurological conditions such as stroke and multiple sclerosis.

How Does Long-Distance Running Affect Myelin?

When the body exhausts its primary energy sources, such as glycogen stored in muscles and the liver, it shifts to burning fat—lipids—for fuel. Since myelin is composed of 70-80% lipids, marathon runners may inadvertently deplete this essential brain fat as they push toward the finish line.

In this observational study, researchers analyzed MRI brain scans of runners before and within 48 hours after completing the 26.2-mile (42.195-km) race. They found significant myelin depletion in 12 brain regions linked to motor coordination, sensory processing, and emotions.

However, there’s a silver lining—follow-up scans showed that myelin levels naturally rebounded two weeks post-race and returned to normal within two months. Notably, this depletion occurred only in specific brain areas, leaving other axon sheaths unaffected.

Interestingly, the reduction in myelin water fraction (MWF) had no connection to a runner’s hydration levels.

“Our findings indicate that marathon running lowers MWF levels in white matter areas, with similar effects in both hemispheres,” the researchers explained. “MWF values gradually recover, reaching pre-run levels within two months. This reversible decline in MWF during prolonged exercise, followed by recovery, suggests that myelin serves as an energy reserve when conventional brain nutrients are scarce. We define this process as metabolic myelin plasticity.”

Unanswered Questions and Future Research

Scientists are still uncertain about the potential effects—if any—of these brain changes in the two months following a marathon. However, the findings open new possibilities for exploring the connection between endurance sports and cognitive function.

More research is needed, as this study analyzed brain scans from only 10 runners (eight male), aged 45–73 years. The study establishes a correlation, but not causation.

“The pilot nature of this observational imaging study comes with limitations,” the researchers noted. “These include a small sample size requiring validation in a larger cohort, challenges in assessing grey matter myelin water fraction (MWF) due to its low myelin content, and limited spatial resolution caused by long scanning times and slight subject movement.”

Despite these constraints, the researchers believe their findings highlight an important link to brain energy metabolism, warranting further investigation.

For now, there’s no evidence that running a marathon negatively impacts short- or long-term cognitive function—though some might joke that signing up for such an intense race in the first place is questionable decision-making.

Read the original article on: New Atlas

Read more: Should You Drink Coffee Before a Race? Insights from a Running Legend and Expert