Effects of Physical Activity, Vascular Burden and Clinical Diagnosis on White Matter Integrity

Background Alzheimer’s disease (AD) is the most common type of dementia. Both degenerative and vascular pathology tend to contribute to dementia as AD coexists with single or multiple cardiovascular risk factors (vascular burden). Modifiable lifestyle factor such as physical activity has been associated with lower vascular burden (VB) and a lower risk of dementia. To test whether physical activity characterised as being inactive or active helped preserve white matter microstructure in a sample consisting of healthy controls and patients from the clinical AD continuum (mild cognitive impairment to dementia) with either low or high VB. Method 213 participants were recruited from three memory clinics and were classified as being either physically active (n = 113) or inactive (n = 100) based on the Cardiovascular Risk Factors, Aging and Dementia (CAIDE) questionnaire. Voxel‐wise tract‐based spatial statistics (TBSS) was carried out using a set of 5000 permutations and threshold‐free cluster enhancement (TFCE) to find significant clusters for fractional anisotropy (FA), axial diffusivity (AxD), mean diffusivity (MD) and radial diffusivity (RD). Result Participants who were physically active had higher FA and lower AxD, MD and RD values relative to the inactive participants. Changes in indices of WM integrity were widespread across the brain covering mainly association and projection tracts but a few commissural tracts. A three‐way interaction effect between Group × Physical Activity × VB was found for FA that was present in mainly projection tracts with a rightward asymmetry along with some association and commissural tracts. Post hocs revealed greater FA in physically active patients with high VB compared with inactive patients with high VB in projection and association/limbic tracts with a rightward asymmetry. Furthermore, the patients with high VB showed higher FA in bilateral projection fibers and cerebellar regions compared with inactive controls with high VB. Conclusion TBSS analysis revealed that high risk patients such as those with high VB achieved the maximum benefit by being physically active as it led to a much greater preservation of white microstructure relative to controls with high VB. This preservation of white matter microstructure was only observed in patients but not in controls.