The association between physical activity and brain integrity is partly mediated by cardiovascular mechanisms

Abstract

AbstractBackgroundPhysical activity (PA) has been associated with decreased risk of dementia, but the mechanisms underlying this association remain to be determined. One hypothesis is that PA might reduce cardiovascular risk factors (CVRFs), which in turn would benefit brain health. Our objective was to assess the role of CVRFs in the association between PA and neuroimaging markers of brain integrity.MethodBaseline data of 134 cognitively unimpaired older adults (mean age: 69) from the Age‐Well cohort were analyzed. They underwent a PA questionnaire, CVRFs collection (systolic blood pressure, body mass index [BMI], current smoker status, HDL‐cholesterol, total cholesterol, and insulin), and multimodal neuroimaging (structural and diffusion MRI, FDG‐ ]and Florbetapir‐PET). A global measure of brain integrity was obtained for each neuroimaging modality by extracting the averaged signal across the whole gray matter (GM), or white matter for diffusion. Correlations were first conducted to assess the association between PA, CVRFs, and each neuroimaging modality. Multiple regression and mediation analyses were then performed to test whether the associations found between PA and neuroimaging were mediated by CVRFs.ResultHigher PA was associated with higher global GM volume and FDG metabolism, but not with amyloid deposition or white matter integrity. Higher PA was also associated with lower insulin levels and BMI, but not with the other CVRFs. Lower insulin and BMI were related to higher GM volume, but not to FDG metabolism. Adjusting for insulin and BMI (separately), the association between PA and FDG metabolism remained unchanged while the association with GM volume did not. When adding insulin and BMI in the same model, BMI was the only significant predictor of GM volume. This was confirmed by a mediation analysis.ConclusionPA is specifically associated with greater brain volume and FDG metabolism in older adults. While the association between PA and FDG metabolism appears to be independent from CVRFs, the link with GM volume is mediated by changes in BMI and insulin, with BMI driving the effects. Our results suggest that maintenance of a healthy BMI through PA could help preventing disturbed insulin metabolism usually observed in aging, thus promoting brain health.