Hypertension, Cognitive Impairment and Dementia: An Epidemiological Perspective

There is increasing interest in the relation of blood pressure with cognitive function and dementia. While some cross-sectional studies have shown an inverse association between blood pressure levels and cognitive impairment or dementia, longitudinal studies have yielded controversial results. Most studies relating blood pressure levels in mid-life with late-life risk of cognitive decline or dementia have reported a harmful effect of hypertension on cognitive function. Studies assessing the effect of late-life blood pressure levels have reported that low diastolic and very high systolic levels may increase the risk. Observational studies and randomized clinical trials provide some evidence for a protective effect of antihypertensive therapy. However, it is possible that in some susceptible older persons lower blood pressure increases the risk of cognitive impairment and dementia. Because hypertension is the main risk factor for cerebrovascular disease, it seems reasonable to expect that vascular cognitive impairment, characterized by executive cognitive impairment, is most affected and this is supported by existing evidence. The impact of hypertension of Alzheimer's disease is controversial and remains to be clarified.