The researchers, who are based at the Mayo Clinic centers in Rochester, Minnesota and Jacksonville, Florida, said aerobic exercise is not just a gym workout but includes walking, and doing chores around the home like shovelling snow and raking leaves.
They searched all the scientific papers they could find on the subject of exercise and cognition, including animal studies and observational studies, lead author and neurologist Dr J Eric Ahlskog told the press.
"We attempted to put together a balanced view of the subject," he added, explaining that they reviewed more than 1,600 papers, 130 of which dealt directly with the issue.
"We concluded that you can make a very compelling argument for exercise as a disease-modifying strategy to prevent dementia and mild cognitive impairment, and for favorably modifying these processes once they have developed," said Ahlskog.
He and his colleagues point out that studies involving brain scans consistently show objective evidence of the benefits of exercise on preserving the integrity of the human brain. They also note that animal studies show exercise produces trophic factors that improve the functioning of the brain, and it also increases connections between brain cells, known as neuroplasticity.
For their study, where possible, they conducted meta-analyses of prospective studies and randomized controlled trials (that is where possible, treating clusters of studies of similar design and measurements as if they were one large study and pooling the data).
Here are some of their more detailed findings:
- Some studies showed signficant reductions in dementia risk linked to midlife exercise.
- Midlife exercise also appeared to reduced risks of mild cognitive impairment (MCI).
- Patients with dementia or MCI had better scores after 6 to 12 months of exercise compared to sedentary controls.
- Healthy adults who did aerobic exercise also showed significantly improved cognitive scores.
- In one large trial of seniors, one year of exercise was linked to significantly larger hippocampal volumes and better spatial memory (cross-sectional studies comparing physically fit with unfit seniors appear to confirm this evidence).
- In other trials with seniors, aerobic exercise was linked to a smaller loss of age-related gray matter.
- fMRI scans showed that connectivity in brain cognitive networks improved after 6 to 12 months of exercise.
- Animal studies suggest exercise increases neuroplasticity by several biological routes, resulting in improved learning.
- Animal studies also show exercise increases brain neurotrophic factors (these help grow and repair brain cells), and there is indirect evidence of the same in humans.
- Exercise may also lessen cognitive decline by cutting cerebrovascular risk, including small vessel disease, which leads to dementia.
"Exercise should not be overlooked as an important therapeutic strategy."
They said more research should be done to look more closely at the relationship between exercise and cognitive function, but they support the idea that in general people should exercise, as Ahlskog explained:
"Whether addressing our patients in primary care or neurology clinics, we should continue to encourage exercise for not only general health, but also cognitive health."