Cardiovascular fitness reflects an organism's ability to supply oxygen to organs such as muscles and the brain. As this ability decreases, the general metabolism becomes less able to adapt easily to varying demands as hemoglobin decreases, venous return deteriorates, stroke volume deteriorates.
The benefits of good cardiovascular fitness for physical health are well documented, and good cardiovascular fitness is also beneficial for the structural integrity of the brain. Although it is often associated with healthy lifestyle behaviors such as physical activity, cardiovascular fitness is not necessarily correlated with it.
Cortical thinning associated with aging in the frontotemporal regions has been associated with cognitive decline in both healthy individuals and those with dementia. No cure currently exists for these dementias.
One potential intervention against the structural decline of the brain associated with aging is to intervene towards midlife on certain aspects of physical health, such as cardiovascular health.
As a measure of the maximum rate at which the body can use oxygen, cardiovascular fitness reflects how efficiently the respiratory and circulatory systems deliver oxygenated blood to the body during active times.
Better cardiovascular fitness has been associated with structural features of gray matter in the brain.
Frontotemporal atrophy is indeed a common archetype of pathological aging and is considered to be one of the main causes of dementia (Fjell et al., 2015; Cox et al., 2021).
Research suggests that aging-related deterioration in white matter structural integrity may be a better signal of later cognitive decline and mild cognitive impairment than gray matter, because white matter may be more sensitive to early aspects of disorderly aging.
Studies examining the links between cardiovascular form and white matter, particularly in younger or cognitively healthy cohorts, where changes in the microstructural integrity of white matter might ignore small distributed changes that might not survive correction for multiple comparisons in the same tract.
Another possible reason for the mixed results seen could be the confusion of cardiovascular fitness with healthy lifestyle behaviors like physical activity.
Lifestyle interventions designed to improve cardiovascular fitness often do so indirectly, for example by increasing physical activity. However, increasing healthy lifestyle habits is not necessarily correlated with better cardiovascular fitness (d'Arbeloff, 2020).
Previous studies using self-report measures of healthy behaviors as an indicator of cardiovascular fitness when examining associations with white matter structural integrity may have yielded different results from studies using direct measures of cardiovascular condition (Sexton et al., 2016; d'Arbeloff, 2020).
In "Midlife Cardiovascular Fitness Is Reflected in the Brain's White Matter" Tracy d'Arbeloff, Ahmad R Hariri and colleagues from New Zealand and USA, used data from members of the Dunedin study to examine possible differential associations between distributed white matter integrity and the two healthy living behaviors (N = 854) and cardiovascular fitness (N = 801). ) in quarantine.
The authors explored possible links between a putative biomarker, the distributed integrity of the brain's white matter, and two intervention targets, cardiovascular fitness and healthy living behaviors, in midlife.
At age 45, fractional anisotropy (FA) derived from diffusion weighted MRI was used to estimate the microstructural integrity of distributed white matter tracts in a population-representative birth cohort. Age-45 cardiovascular fitness (VO2Max; N = 801) was estimated from heart rates obtained during submaximal exercise tests; age-45 healthy lifestyle behaviors were estimated using the Nyberg Health Index (N = 854).
Ten-fold cross-validated elastic net predictive modeling revealed that estimated VO2Max was modestly associated with distributed FA. In contrast, there was no significant association between Nyberg Health Index scores and FA.
The findings of the authors suggest that cardiovascular fitness levels, but not healthy lifestyle behaviors, are associated with the distributed integrity of white matter in the brain in midlife. These patterns could help inform future clinical intervention research targeting dementia.