As people age, certain brain regions decrease in volume, resulting in a decline in cognitive capacity. This extent to which this occurs is highly variable between individuals and can be influenced by a wide range of factors – including one’s level of physical fitness in middle age, according to a new study.
Appearing in the journal Neurology, the research paper outlines an experiment that sought to determine how differences in participants’ cardiovascular fitness, blood pressure, and heart rate might affect their brain size later in life. Spanning a period of two decades, the project involved more than 1,000 people enrolled in the Framingham Heart Study, with an average age of 40 at the start of the experiment.
The first phase of the study took place between 1979 and 1983, during which time participants were recruited to perform a running task on a treadmill while researchers monitored their heart rate and blood pressure in order to calculate their exercise capacity. This provides a measure of the maximum rate at which the body is able to consume oxygen.
Then, from 1998 to 2001, participants were revisited and asked to repeat the task, before undergoing an MRI scan in order to examine their total cerebral brain volume (TCBV).
Although researchers did not calculate subjects’ exercise capacity during this second round of tests, they were able to identify certain correlations between baseline fitness levels and TCBV 20 years later.
The average exercise capacity of participants at the start of the experiment was 39 millilitres of oxygen per kilogram of body mass, although those who performed below this level were found to have smaller brains by the time the MRI scans were conducted. More precisely, the study authors report that a reduction of 8 millilitres of oxygen per kilogram of body mass in baseline exercise capacity corresponded to a TCBV decrease equivalent to one additional year of brain shrinkage at the end of the two decades.
Of all the variables measured, heart rate was found to have the greatest impact on TCBV, with those who had a higher heart rate at the start of the experiment being most likely to exhibit accelerated brain shrinkage later in life. Though this reduction in size was noted across the brain, it was found to be most pronounced in the frontal lobe. This is significant since degeneration in this part of the brain is often associated with dementia, suggesting a possible link between poor cardiovascular fitness in middle age and greater cognitive decline in old age.
However, the study authors point out that their research is merely observational, and that while a link between lower exercise capacity and decreased TCBV is identified, no evidence is provided regarding the actual effect of poor cardiovascular fitness on cognition. Furthermore, because MRI scans were not conducted at the start of the experiment, the research only provides information about total brain size at the end of the two decades, but does reveal how much brain shrinkage each participant actually suffered over that period.