For the results, the research team conducted three studies--in the first study, the researchers examined 317 participants enrolled in the Wisconsin Registry for Alzheimer's Prevention, an ongoing observational study of more than 1,500 people with a history of parents with probable Alzheimer's dementia.
In the second study, researchers studied 95 people, also from the registry, who were given scores called polygenic risk scores, based on whether they possessed certain genes associated with Alzheimer's.
Similarly, the third study examined MRIs from 107 individuals from the registry who were asked to run on a treadmill to determine their oxygen uptake efficiency slope, a measure of aerobic fitness.
Participation in the registry included an initial assessment of biological, health and lifestyle factors associated with the disease and follow-up assessments every two to four years.
All participants completed a questionnaire about their physical activity and underwent neuropsychological testing and brain scans to measure several biomarkers associated with Alzheimer's disease.
The researchers compared data from individuals younger than 60 years with older adults and found a decrease in cognitive abilities as well as an increase in biomarkers associated with the disease in older individuals.
However, the effects were significantly weaker in older adults who reported engaging in the equivalent of at least 30 minutes of moderate exercise five days a week.
"The most interesting part of our research is that we now show evidence that lifestyle habits - in this case regular, moderate exercise - can modify the effect of what is commonly considered a non-modifiable risk factor for Alzheimer's, in this case, aging," Okonkwo said.
"Overall, these studies suggest that the negative effect of aging and genetic risk on Alzheimer's' disease biomarkers and cognition can be lessened in physically active, older adults at risk for the disease compared with their less active peers."