Older adults with higher baseline systolic blood pressure (SBP) levels have a lower risk for incident dementia, and more distinctly U-shaped associations between SBP and dementia risk were observed only in those older than 75 years, according to a study in JAMA Internal Medicine.
Data on the association between late life high BP and dementia risk are limited. Although some studies have found an association with increased risk, most suggest there is a neutral or decreased risk associated with higher BP. A possible explanation from previous and limited data suggest a U-shaped relationship exists in late life where both high and low BP are tied to dementia risk.
The objective of the current study was to investigate whether the association between SBP and dementia risk is U-shaped and whether age and comorbidity play a role in this association.
The findings are based on an analysis of 7 prospective, observational, population-based cohort studies that assessed incident dementia in older individuals. Inclusion criteria were the availability of BP measurements in participants without dementia and subsequent data regarding incident dementia. The studies were initiated from 1987 to 2006 in Europe and the United States, and data analysis was performed between November 7, 2019, and October 3, 2021.
The studies included a total of 17,286 participants (mean [SD] baseline age, 74.5 [7.3] years; 60.1% women), of whom 2799 (16.2%) had incident dementia. The median (interquartile range) time to diagnosis was 7.3 (5.2-11.0) years, or 136,473 person-years.
SBP and dementia risk approached an inverse linear association, in which the low point of the U-shape occurred at a high BP level, with an SBP of 185 mm Hg (95% CI, 161-230 mm Hg; P =.001) associated with the lowest dementia risk. The lowest risk point was with 160 mm Hg (95% CI, 154-181 mm Hg; P <.001) for mortality and 163 mm Hg (95% CI, 158-197 mm Hg; P < .001) for the combination of dementia and mortality.
The associations were more distinctly U-shaped in individuals aged 75 to 95 years, with the lowest risk points at about 165 mm Hg (range, 158 mm Hg [95% CI, 152-178 mm Hg; P <.001] to 170 mm Hg [95% CI, 160-260 mm Hg; P =.004]).
The lowest risk points for mortality increased with age, from 134 mm Hg (95% CI, 102-149 mm Hg; P =.03) in individuals aged 60 to 70 years to about 160 mm Hg in those aged ≥70 years (range, 155 mm Hg [95% CI, 150-166 mm Hg; P <.001] to 166 mm Hg [95% CI, 154-260 mm Hg; P =.02]).
The combined dementia and mortality risk curves were similar to those for mortality, and the observed associations were less distinct for diastolic BP.
Significant interactions were found for SBP regarding baseline antihypertensive medication use and mortality (Akaike information criterion [AIC], –5.1; P for interaction = .01) and combined dementia and mortality (AIC, –2.2; P for interaction = .04) but not for dementia (AIC, 1.4; P for interaction = .27).
The researchers noted that the studies were conducted in different periods and countries and involved varying methods of BP lowering, population disease burden, and life expectancy, and the findings are based on observational data. Also, antihypertensive medication use may have been initiated after BP and covariates were evaluated at baseline.
“The results of this study suggest that lower SBP in older people overall may indicate a higher dementia risk, U-shaped associations only occur in older age groups, and these associations cannot be explained by lower mortality owing to lower SBP,” the researchers stated.
van Dalen JW, Brayne C, Crane PK, et al. Association of systolic blood pressure with dementia risk and the role of age, U-shaped associations, and mortality. JAMA Intern Med. Published online December 13, 2021. doi:10.1001/jamainternmed.2021.7009