Research links cardiovascular fitness to brain health

The white matter of the brain includes areas of the central nervous system that consist of myelinated axons. The name is derived from the pale appearance of the lipids that make up myelin. Myelin is a segmented sheath that insulates axons and conducts neural signals. The loss of myelin has been documented in a number of neurodegenerative pathologies, including Alzheimer’s and Parkinson’s diseases, and perhaps most prominently, multiple sclerosis. As people age, demyelination becomes more likely.

Researchers have long suspected a link between cardiorespiratory fitness and the integrity of the brain’s white matter as people age. However, a lack of specific evidence led researchers at the National Institutes of Health to conduct a study on the strength of this correlation. published in the Proceedings of the National Academy of Sciences.

To establish a link between cardiovascular fitness and cerebral myelination, the researchers recruited a cohort of 125 participants ranging in age from 22 to 94 years old. The cardiovascular fitness of the participants was quantified as the maximum oxygen consumption, colloquially and succinctly known as VO₂maximum Myelin content was defined as the myelin water fraction, which the researchers estimated using an advanced multicomponent relaxometry MRI method.

Previous studies using conventional techniques were unable to isolate myelin from other brain material; the new MRI technique used here is more sensitive and specific for measuring myelin content in vivo. Recent studies using multicomponent relaxometry MRI have even shown correlations between local myelin water fraction with cerebral blood flow and motor function, both of which are influenced by cardiorespiratory fitness, which in turn motivated the NIH researchers to continue the current study using the same technology to continue.

Results

The researchers report that higher cardiorespiratory fitness strongly correlates with greater cerebral myelination. Furthermore, higher cardiorespiratory fitness was associated with better myelin integrity, which was particularly noticeable in middle-aged and older participants.

In particular, they found significant positive correlations between the two measurements in the frontal lobes and white matter tracts – areas prone to early degeneration associated with neurological disorders at the onset of old age. They suggest that cardiorespiratory fitness is likely to provide significant protection for these sensitive brain regions, especially in subjects with lifelong fitness.

The researchers note that they were unable to establish a causal relationship between improved cardiorespiratory fitness and improved myelin integrity and that their results represent a correlation only.

“Nonetheless, our findings suggest that cardiorespiratory fitness is likely a valuable indicator of overall health and a potential target for interventions aimed at promoting brain health,” they write.

The study also points to the association of aerobic exercise with neuroprotective adaptations in the brain, as well as the upregulation of neurotrophins and brain-derived neurotrophic factors, which increase brain mitochondrial function. Decreases in mitochondrial function have previously been linked to diseases due to demyelination.

The researchers suggest that future studies could use their work to study the relationship between physical fitness, brain health and myelin integrity to support brain aging and prevent neurological disorders.

They write: “Additionally, this work lays the foundation for further research into the potential therapeutic applications of improving cardiorespiratory fitness or myelination to promote healthy brain aging and combat age-related neurodegeneration, including in Alzheimer’s disease.”

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