HQ Team
April 6, 2025: Marathons may affect the brain causing the organ to eat itself to make up for fuel lost during the run, and the effect is reversible, according to Spanish researchers.
Researchers at Spain’s Center for Cooperative Research in Biomaterials (CIC biomaGUNE), Basque Research and Technology Alliance (BRTA), and Donostia-San Sebastián found that the brain may turn to cellular fat to maintain extreme metabolic conditions.
These findings indicate that myelin (a substance that surrounds the neurons) exhibits previously unknown behaviour and contributes towards the brain’s energy metabolism when other sources of energy are running low, according to a CIC biomaGune statement.
Understanding how myelin in marathon runners recovers quickly may provide clues for developing treatments for demyelinating diseases such as multiple sclerosis in which the disappearance of myelin and, therefore, of its energy contribution, facilitates structural damage and degeneration, the researchers said.
A decline in amount of myelin
The study conducted with the help of researchers from the UPV/EHU, and IIS Biobizkaia shows that people who run a marathon experience a decrease in the amount of myelin in certain areas of the brain. Myelin is a substance that makes up the protective sheath that coats nerve fibres.
According to the study published by Nature Metabolism, this effect is reversed two months after the marathon.
Exercise for a long time forces the human body to resort to its energy reserves. When running a marathon, for example, the body mainly consumes carbohydrates, such as glycogen, as a source of energy, but it resorts to fats when the glycogen in the muscles is used up.
Myelin, which surrounds neurons in the brain and acts as an electrical insulator, mainly comprises lipids and previous research in rodents suggests that these lipids can act as an energy reserve in extreme metabolic conditions.
Carlos Matute, Professor of Anatomy and Human Embriology at the UPV/EHU and a researcher at IIS Biobizkaia, and Pedro Ramos-Cabrer, Ikerbasque Research Professor at CIC biomaGUNE, together with Alberto Cabrera-Zubizarreta, a radiologist at HT Médica, used magnetic resonance imaging to obtain images of the brains of ten marathon runners (eight men and two women) before and 48 hours after the 42-kilometre race.
Measuring the fraction of myelin water
The researchers took images of the brains of two of the runners two weeks after the race, and of six runners two months after the race as a follow-up.
By measuring the fraction of myelin water in the brain —an indirect indicator of the amount of myelin— the authors discovered “a reduction in the myelin content in 12 areas of white matter in the brain, which are related to motor coordination and sensory and emotional integration,” said Carlos Matute.
Two weeks later, “the myelin concentrations had increased substantially, but had not yet reached pre-race levels”, Pedro Ramos said. The authors said that the myelin content had recovered fully two months after the marathon.
White matter is made up of a large network of nerve fibres in the brain that allows the exchange of information and communication between different areas of the brain. It’s called “white matter” because the nerve fibres are covered in a protective sheath called myelin, which gives the tissue its white colour.
‘Larger cohort needed’
The researchers concluded that “myelin seems to act as an energy source when other brain nutrients are depleted during endurance exercise, and that further research is needed to establish how extreme exercise is related to the amount of myelin in the brain. Trials in a larger cohort are needed,” said Ramos-Cabrer.
Matute said: “The brain’s energy metabolism is more complex than previously thought. The use of myelin as brain fuel opens up new insights into the brain’s energy requirements.”
According to the authors, more studies are needed to assess whether these changes exert any effect on the neurophysiological and cognitive functions associated with these regions, but they point out that most of the myelin in the brain is not affected.
