One characteristic of neurodegenerative conditions such as Alzheimer's disease and Parkinson's disease is the deterioration of myelin, the protective sheath surrounding nerve cells in the white matter of the brain. Conserving myelin may be an effective way to prevent or treat these conditions, and a new study suggests one good way to help do that.

Greater cardiorespiratory fitness has been associated with better brain function, but few, if any, studies have been done to test this theory. Researchers at the National Institute on Aging recently found that cardiorespiratory fitness conserves myelin. Looking at a study population of adults between the ages of 22 and 94, they reported that the association between cardiorespiratory fitness and the amount of myelin, or myelination, was the strongest in middle-aged and older adults.

The connection between cardiorespiratory fitness and the amount of myelin, or myelination, was the strongest in middle-aged and older adults.

The relationship between cardiorespiratory fitness and myelination was particularly strong in parts of the brain susceptible to early deterioration in Alzheimer's disease, such as the frontal lobe. The study findings provide evidence that interventions that focus on aerobic fitness may help conserve myelin and maintain cognitive function.

“We kind of anticipated some association between cardiorespiratory fitness and brain myelination,” Mustapha Bouhrara, corresponding author on the study, told TheDoctor because the benefits of aerobic exercise for the brain have been shown in many studies.

The current study provided evidence for that relationship at a more cellular level.

Data from 125 people enrolled in two studies were analyzed for the current paper. Study participants had no cognitive impairment. Cardiorespiratory fitness was determined by measuring the maximum rate of oxygen consumption (VO2max) during strenuous exercise. The amount of myelination in the brain was determined by measuring myelin water fraction using magnetic resonance imaging.

The relationship between cardiorespiratory fitness and myelination was particularly strong in parts of the brain susceptible to early deterioration in Alzheimer's disease, such as the frontal lobe.

Although the study findings demonstrate an association between cardiorespiratory fitness and myelination, they do not prove causality, the researchers cautioned. Going forward, the findings will need to be replicated in a larger and more diverse study population to provide more evidence of the connection between cardiorespiratory fitness and myelination, Bouhrara, the Stadtman Principal Investigator in the Laboratory of Clinical Investigation at the National Institute on Aging, explained.

His team is talking about doing a longitudinal study where subjects are followed over time to measure their myelin and cardiorespiratory fitness. “We would be able to see if improvement in cardiorespiratory fitness immediately improves myelination or if a decline in cardiorespiratory fitness results in an immediate decline in myelination,” Bouhrara added.

The study is published in the PNAS, Proceedings of the National Academy of Science.