Physical activity has been associated with decreased dementia risk in recent studies, but the effects for structural brain changes (i.e. white matter lesions (WML) and/or brain atrophy) have remained unclear. The CAIDE participants were a random population-based sample studied in midlife and re-examined on average 21 years later (n=2000). A subpopulation (n=75; 31 control, 23 MCI, 21 dementia) was MRI scanned at the re-examination. T1-weighted images were used to investigate grey matter (GM) density, and FLAIR-images for WML rating. Persons who actively participated in physical activity at midlife tended to have larger total brain volume (β 0.12; 95% CI 0.17-1.16, p=0.10) in late-life than sedentary persons even after adjustments. GM volume was larger among the active (β 0.19; 95% CI 0.07-1.48, p=0.03), whereas the association between midlife physical activity and larger WM volume became non-significant (β 0.03; 95% CI -0.64 to 0.86, p=0.77) after full adjustments. The differences in the GM density localized mainly in frontal lobes. There was no significant association between midlife physical activity and severe WML later in life after full adjustments (OR 4.20, 95% CI 0.26-69.13, p=0.32).
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