Blood pressure and dementia in the very old : an epidemiologic study

There is a considerable public health interest in the vascular causes of dementia because they are potentially treatable and preventable. A number of vascular factors may be associated with dementia. Hypertension is supposed to be the most powerful vascular risk factor for dementia because of its contribution to cerebrovascular disease. However, there have only been a few population-based studies about the direct relationship between blood pressure (BP) and dementia.

We used the baseline and first follow-up data from the Kungsholmen Project to examine the relationship between BP and dementia. The project is a longitudinal study on aging and dementia, including all inhabitants of the Kungsholmen district in Stockholm aged 75 years and older on October 1, 1987. Of the eligible subjects, 1810 (77%) participated in the initial survey (baseline) in which the Mini-Mental State Examination (MMSE) was used as a screening test for dementia. The Diagnostic and Statistical Manual of Mental Disorders, Third Edition-Revised diagnostic criteria were used to define dementia. During 1992-94, the following groups received thorough clinical examinations: 1) the initial cohort, 2) all inhabitants of the Kungsholmen district who were born in 1915, and 3) all residents of the St Göran district who were born in 1902 and before. There was a cross-sectional relationship between relatively low BP (systolic <140 or diastolic <75 mm Hg) and dementia or cognitive impairment (MMSE <24). In other words, the prevalence of dementia or cognitive impairment was higher in subjects with relatively low BP. The correlation between low BP and cognitive impairment partially accounted for the increased mortality associated with low BP (systolic <130 or diastolic <75 mm Hg).

Longitudinal BP reduction (decrease more than 5 mm Hg from baseline to follow up) was related to increased incidence of dementia, which may explain the cross sectional association between relatively low BP and dementia. We suggest: 1) BP reduction is an early pathophysiological change in a dementia process, particularly Alzheimer's disease; 2) clinically unrecognized vascular lesions in the brain or atherosclerosis are responsible for both dementia and BP reduction. In addition, baseline systolic BP >180 mm Hg was related to an increased risk of developing dementia (relative risk 1.6, 95% confidence interval 1.1 -2.6) compared to systolic BP of 141-160 mm Hg. The association was not explained by age or gender, but was somewhat reduced when all co-variables including stroke were included in the model.