Blood Pressure and Risk of Vascular Dementia

V ascular dementia is the second most common cause of dementia 1 and is increasing in prevalence in developing countries. 2 Vascular dementia usually occurs in association with vascular risk factors or after transient ischemic attack (TIA) or stroke 3 and commonly manifests with a decline in cognitive function, apathy, and depression, and can eventually result in death. 1,4 Blood pressure (BP), a known causal risk factor for stroke, 5 has also been identified as a potential risk factor for vascular dementia. 6 However, studies have reported conflicting results on the relation between BP and vascular dementia (Table I in the online-only Data Supplement). 6 Previous analyses of healthy cohorts and patients with previous diagnosis of TIA or stroke have suggested a positive association between midlife BP (age 40–50 years) and future development of dementia, including vascular dementia. 7–9 However, several other studies have suggested that low BP in old age is associated with an increased risk of dementia (Table I in the online-only Data Supplement). The reported negative associations between BP and risk of vascular dementia at older ages may be caused by reverse cau-sality, that is, vascular dementia causing low BP, because of loss of sympathetic drive, rather than low BP causing vascu-lar dementia. 12 Null or negative associations could also result from the prior prescription of BP-lowering drugs. Previous studies have been relatively small, limiting their ability to Background and Purpose—Vascular dementia is the second most common form of dementia but reliable evidence on age-specific associations between blood pressure (BP) and risk of vascular dementia is limited and some studies have reported negative associations at older ages. Methods—In a cohort of 4.28 million individuals, free of known vascular disease and dementia and identified from linked electronic primary care health records in the United Kingdom (Clinical Practice Research Datalink), we related BP to time to physician-diagnosed vascular dementia. We further determined associations between BP and dementia in a prospective population-based cohort of incident transient ischemic attack and stroke (Oxford Vascular Study). Results—For a median follow-up of 7.0 years, 11 114 initial presentations of vascular dementia were observed in the primary care cohort after exclusion of the first 4 years of follow-up. The association between usual systolic BP and risk of vascular dementia decreased with age (hazard ratio per 20 mm Hg higher systolic BP, 1. remained predictive of vascular dementia after accounting for effect mediation by stroke and …