Blood pressure levels before dementia.

Background: The association between blood pressure (BP) and dementia is not easily interpreted, but some prospective studies suggest that dementia may lower BP.

Objective: To examine the relationship between BP during a 10-year period and the prevalence of dementia.

Design: Comparison of longitudinal BP between participants who had dementia, participants who were cognitively impaired, and unimpaired participants selected from an ongoing cohort study.

Setting: A prepaid health plan in southern California.

Participants: Three hundred participants had dementia, 285 were cognitively impaired, and 585 were unimpaired.

Main Outcome Measures: Retrospective medical record review of up to 3 randomly selected BP measurements per year for the 10 years before cognitive classification of each participant.

Results: Systolic BP increased with time in the unimpaired participants, and increased less in women who developed cognitive impairment and in women who developed dementia. Diastolic BP declined significantly (P<.001) with time in all 3 groups. Compared with unimpaired women, the adjusted rate of decline in diastolic BP was significantly (P = .04) greater for the women who developed dementia.

Conclusions: These findings are consistent with previous findings that the relationship between BP and dementia is affected by age at data collection. Valid inferences about the effect of BP on the development of dementia require prospective data collection in which subjects are free of dementia or cognitive impairment at enrollment.