Increased diastolic blood pressure is associated with MRI biomarkers of dementia-related brain pathology in normative ageing

Background: hypertension is a risk for brain ageing, but the mechanisms underlying this effect remain unclear. Magnetic resonance imaging (MRI) detected biomarkers of brain ageing include white matter hyperintensities (WMHs), a marker of cerebrovascular disease, and hippocampal volume, a marker of Alzheimer's disease pathology. Objective: to examine relationships between blood pressure (BP) components and brain pathology in older adults. Subjects: two hundred and twenty-seven members of the Aberdeen 1936 Birth Cohort between ages 64 and 68 years. Methods: BP was assessed biennially between 64 and 68 years and brain MRI performed at 68 years. The risk factors of interest were diastolic and systolic BP and their visit-to-visit variability. Outcomes were WMH abundance and hippocampal volume. Regression models, controlling for confounding factors, examined their relationships. Results: higher diastolic BP predicted increased WMH (β = 0.13, P = 0.044) and smaller hippocampi (β = -0.25, P = 0.006). In contrast, increased systolic BP predicted larger hippocampi (β = 0.22, P = 0.013). Variability of diastolic BP predicted lower hippocampal volume (β = -0.15, P = 0.033). These relationships were independent of confounding life-course risk factors. Anti-hypertensive medication did not modify these relationships, but was independently associated with increased WMH (β = 0.17, P = 0.011). Conclusion: increased diastolic BP is associated with biomarkers of both cerebrovascular and Alzheimer's diseases, whereas the role of systolic BP is less clear, with evidence for a protective effect on hippocampal volume. These differing relationships emphasise the importance of considering individual BP components with regard to brain ageing and pathology. Interventions targeting diastolic hypertension and its chronic variability may provide new strategies able to slow the accumulation of these harmful pathologies.