Cardiovascular Fitness Boosts Brain Health

The myelinated axons that make up the central nervous system’s white matter are found in certain regions of the brain. The name comes from the lipids that make up myelin’s pale hue. The segmented sheath known as myelin protects axons and facilitates the transmission of nerve impulses. A number of neurodegenerative diseases, including as Parkinson’s and Alzheimer’s, as well as multiple sclerosis, are known to be associated with myelin loss. Demyelination becomes increasingly common as people get older.

Scholars have long conjectured that the integrity of the white matter in the aging brain is correlated with cardiorespiratory fitness. The National Institutes of Health conducted a study to determine the strength of this association, but they were unable to find any particular proof. The results of their investigation were published in the Proceedings of the National Academy of Sciences.

In order to determine if brain myelination and cardiovascular fitness are correlated, the researchers gathered a cohort of 125 individuals, ranging in age from 22 to 94. The maximal rate of oxygen consumption, or VO2max as it is commonly and concisely termed, was used to quantify the participants’ cardiovascular fitness. The myelin water fraction, which the researchers calculated using an advanced multicomponent relaxometry MRI technique, was defined as the myelin content.

The new MRI technique used here is more sensitive and specific to assessing myelin levels in vivo, as previous studies using traditional techniques were unable to separate myelin from other brain matter. Indeed, correlations between local myelin water fraction and cerebral blood flow and motor function—both of which are impacted by cardiorespiratory fitness—were found in recent studies employing multicomponent relaxometry MRI. These findings inspired the NIH researchers to conduct the current study using the same technology.

The researchers found a robust correlation between increased cerebral myelination and enhanced cardiorespiratory fitness. Additionally, improved myelin integrity was linked to increased cardiorespiratory fitness, which was especially evident in the middle-aged and older subjects.

Their findings are noteworthy because they discovered strong positive associations between the two measurements in the frontal lobes and white matter tracts, areas that are prone to early degradation linked to neurological diseases that manifest in early aging. They imply that, especially in the case of the individuals who have maintained a lifetime of fitness, cardiorespiratory fitness is probably going to be highly protective for these delicate brain regions.

The researchers point out that their findings simply show a correlation and that they were unable to demonstrate a causal relationship between enhanced myelin integrity and higher cardiorespiratory fitness.

“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,” they state.

The paper also mentions the overexpression of neurotrophins and brain-derived neurotrophic factor, which improves brain mitochondrial function, and the link between aerobic exercise and neuroprotective adaptations in the brain. Diseases brought on by demyelination have previously been linked to declines in mitochondrial activity.

In order to support brain aging and prevent neurological problems, the researchers propose that future studies might make use of their work to examine the association between physical fitness, brain health, and myelin integrity.

They write, “Additionally, this work lays the foundation for further investigations 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.”

For more information: Evidence of association between higher cardiorespiratory fitness and higher cerebral myelination in aging, Proceedings of the National Academy of Sciences, https://doi.org/10.1073/pnas.2402813121