The researchers — from the University of Texas Southwestern Medical Center in Dallas — think that their study is the first to use an objective measure of aerobic capacity to assess the relationship between white matter integrity, cognitive performance, and cardiorespiratory fitness in older individuals with mild cognitive impairment (MCI).
"This research," explains first study author Kan Ding, an assistant professor of neurology and neurotherapeutics, "supports the hypothesis that improving people's fitness may improve their brain health and slow down the aging process."
She and her team report their findings in a paper that was published in the Journal of Alzheimer's Disease.
People with MCI have noticeable problems with memory and reasoning, but they are not serious enough to interfere with daily living or the ability to take care of oneself. Research suggests that "15–20 percent of those aged 65 and older may have MCI."
Study measured VO2max to assess fitness
The causes of MCI are not yet fully understood, although experts suggest that in some cases it may result from brain changes that occur in the very early stages of Alzheimer's disease or other types of dementia.
The factors that raise the risk of developing MCI are the same as those that raise a person's risk of dementia — such as advancing age, having conditions that increase the risk of cardiovascular disease, and having a family history of dementia.
MCI often precedes dementia, but not everyone with MCI will develop dementia. In some, it can revert to normal cognitive functioning or simply not advance.
There are several types of MCI, depending on which aspect of cognition is most affected. The new study investigated people with amnestic MCI.
Amnestic MCI mostly affects memory and could give rise to problems such as forgetting names, appointments, events, conversations, or other information that would previously not have been difficult to recall.
For their investigation, Prof. Ding and her colleagues recruited 81 participants aged 65, on average. Of these, 55 were people with amnestic MCI and 26 were healthy individuals without MCI (the controls).
The team assessed the participants' cardiorespiratory fitness by measuring their maximal oxygen uptake (VO2max) during an aerobic exercise test.
Lower fitness linked to weaker white matter
The participants, 43 of whom were female, also completed assessments of memory and reasoning and underwent diffusion tensor imaging (DTI), which is a type of scan that is used to assess the integrity of the nerve fibers that make up the white matter in the brain.
The brain's white matter houses "millions of bundles of nerve fibers" that connect brain cells, or neurons, in all parts of the brain and allow them to convey messages to each other.
With DTI, researchers can assess the extent to which the white matter fibers have deteriorated in selected parts of the brain.
The results showed that the MCI patients and the healthy controls had no differences in global white matter fiber integrity and VO2max. However, closer examination showed that lower aerobic fitness was linked to weaker white matter in some parts of the brain.
The researchers note that the link "remained statistically significant after adjustment of age, sex, body mass index, [white matter] lesion burden, and MCI status."
Evidence of exercise's benefit to brain health
The study also found that, in the case of the people with MCI, DTI measures from the brain areas in which low white matter integrity was linked to poorer aerobic fitness correlated with performance on the memory and thinking tests.
Thus, higher levels of aerobic fitness are linked to better integrity of the brain's white matter, "which in turn is correlated with better executive function performance in MCI patients," the authors conclude.
The research adds to a growing body of evidence on the value of exercise to brain health as we advance in age.
Earlier work led by one of the team showed that messages are passed more efficiently between brain cells in seniors who exercise.
Other examples include a more recent study that suggested that aerobic exercise "may be key" for Alzheimer's prevention, and another that found that walking 4,000 steps per day can "boost brain function."
"A lot of work remains to better understand and treat dementia. But, eventually, the hope is that our studies will convince people to exercise more."
Prof. Kan Ding