Physical fitness protects the health of sensitive brain regions

Researchers have revealed new details about the fascinating connection between cardiovascular fitness and brain health. 

Previous studies indicated that maintaining good cardiorespiratory fitness (CRF) played an important role in preserving the integrity of the brain’s white matter, yet this theory had not been fully investigated.

The role of white matter during aging

The brain’s white matter consists of areas of the central nervous system made up of myelinated axons. The name “white matter” originates from the pale appearance of the lipids comprising myelin – a segmented sheath that insulates axons and thus ensures the conduction of neural signals. 

Myelin loss occurs in various neurodegenerative diseases, including Alzheimer’s and Parkinson’s, and most notably, multiple sclerosis. As people age, the risk of demyelination increases.

Cardiorespiratory fitness and white matter integrity 

Scientists have long suspected a connection between cardiorespiratory fitness and the integrity of the brain’s white matter during the aging process. However, the lack of specific evidence prompted a team of researchers at the National Institutes of Health (NIH) to conduct a study examining the strength of this correlation.

To investigate these issues, the experts recruited 125 participants aged 22-94, and quantified their cardiovascular fitness as the maximum rate of oxygen consumption, known as VO2max. The myelin content was defined as the myelin water fraction, which the scientists estimated through an advanced multicomponent relaxometry MRI method.

Isolating myelin from other brain matter 

“Research suggests that maintaining good cardiorespiratory fitness plays a role in preserving white matter integrity. However, there is scarcity of clinical studies examining the relationship between CRF and myelin integrity,” noted the study authors. 

“Here, we investigated the association between CRF, as measured by the maximum rate of oxygen consumption (VO2max), and myelin content, as defined by the myelin water fraction (MWF) MRI, throughout the adult lifespan.”

While previous analyses relying on conventional techniques did not succeed in isolating myelin from other brain matter, this new MRI method is more sensitive and specific to measuring myelin content in vivo. 

Cerebral blood flow and motor function

Recent studies using multicomponent relaxometry MRI found important correlations between local myelin water fraction and cerebral blood flow and motor function, which are both influenced by cardiorespiratory fitness. This motivated the NIH researchers to conduct the current study using the same technology.

The investigations revealed that greater cardiorespiratory fitness correlated strongly with higher cerebral myelination. In addition, greater cardiorespiratory fitness was found to be associated with better myelin integrity, particularly in middle-aged and older participants.

Protecting sensitive brain regions 

Most importantly, the experts discovered significant positive correlations between the two measures in the frontal lobes and white matter tracts, which are the regions most susceptible to early degeneration caused by neurological disorders at the onset of old age. 

These findings suggest that cardiorespiratory fitness is likely to be protective for these sensitive brain regions, especially among the participants with lifelong fitness.

However, this study cannot establish a direct causal link between higher cardiorespiratory fitness and improved myelin integrity, its results showing just a correlation between the two.

“Nevertheless, our findings suggest that cardiorespiratory fitness is likely to be a valuable indicator of overall health and a potential target for interventions aimed at promoting brain health,” the authors wrote.

Physical fitness and brain health

The experts also discovered an association between aerobic exercise and neuroprotective adaptations in the brain, along with the upregulation of neurotrophins and brain-derived neurotrophic factor, which helps increase brain mitochondrial function. Declines in this function have been linked by previous studies to diseases resulting from demyelination.

Future research could use this work to examine the relationship between physical fitness, brain health and myelin integrity to find ways of supporting brain aging and preventing neurological disorders.

“This original study provides compelling evidence of the crucial role of CRF in the preservation of myelin integrity with advancing age, expanding our understanding of the intricate relationship between cardiovascular health and white matter microstructure,” noted the researchers.

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

The study is published in the journal Proceedings of the National Academy of Sciences.

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