Blood Pressure and Risk of Vascular Dementia

Abstract

Purpose: Vascular dementia is the second most common form of dementia and poses a significant clinical and economic burden. The association between blood pressure and risk of vascular dementia is unclear. Methods: A cohort of 4.28 million individuals, free of vascular disease and de mentia, was identified from linked electronic health records. Cox models were used to analyse time to initial presentation of physician-diagnosed vascular dementia, adjusted for age, BMI, gender and smoking status. Models were further adjusted for incidence of stroke and transient ischemic attack, to estimate what proportion of the association between systolic blood pressure (SBP) and risk of vascular dementia was mediated by clinically diagnosed cerebrovascular disease. Results: Over a median follow up of 7.0 years, 11 114 initial presentations of vascular dementia were observed after exclusion of the first four years of follow up. The association between 20 mm Hg higher usual SBP and risk of vascular dementia declined with increasing age, from an HR of 1.62 (CI 1.13, 2.35) in the age group of 30 to 50, to an HR of 1.26 (CI 1.18, 1.35) in the age group of 51 to 70, to an HR of 0.97 (CI 0.92, 1.03) in the age group 71 to 90 (p trend = 0.006). 30% of excess risk of vascular dementia associated with higher SBP in the age group 30-70 was mediated through incident stroke and transient ischemic attack. Conclusions: Although blood pressure is positively associated with risk of vascular dementia, the association declines with increasing age. Previously reported inverse associations between blood pressure and vascular dementia in old age are likely due to reverse causality. Assuming causality, individual and populationlevel efforts to reduce blood pressure and prevent stroke and transient ischemic attack may reduce the incidence of vascular dementia.