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Association of Systolic Blood Pressure With Dementia Risk
Quick Takes
- This study set out to evaluate the optimal systolic blood pressure (SBP) associated with the lowest risk of dementia among various age groups.
- Overall, dementia risk was lower for individuals with higher BP at baseline, while in older patients, a U-shaped association between SBP and dementia was seen.
- In contrast, both mortality and the combined outcome of mortality and dementia had clear U-shaped associations with SBP, with the lowest risk SBP gradually increasing from the 130s in the youngest group to the 160s in those >75 years old.
Study Questions:
What is the optimal systolic blood pressure (SBP) to minimize the risk of dementia? Is the association between SBP and dementia risk U-shaped, and do age and comorbidity play a role in this association?
Methods:
This analysis included seven prospective, observational, population-based cohort studies designed to evaluate the incidence of dementia in older adults. The various studies ran between 1987 and 2006 in Europe (Spain, Sweden, Germany, the Netherlands) and the United States. Study duration ranged from 5–26 years. Participants did not have a diagnosis of dementia at baseline, had BP measurements available at the time of entry, and were followed and assessed for the development of dementia. Dementia was defined using Diagnostic and Statistical Manual of Mental Disorders (Third Edition Revised) or Diagnostic and Statistical Manual of Mental Disorders (Fourth Edition) criteria. All studies had regular cognitive screening, short follow-up time intervals, and few participants who were lost to follow-up.
The main outcomes were all-cause dementia, mortality, and combined dementia and mortality. Covariates were baseline antihypertensive medication use (yes or no), sex, educational level, body mass index, smoking status, diabetes, stroke history, myocardial infarction history, and polypharmacy. Data on race and ethnicity were not collected.
Results:
The cumulative population of the seven studies was 17,286 participants, 60.1% women, and mean baseline age was 74.5 ± 7.3 years. A total of 2,799 (16.2%) participants developed dementia with a median time to diagnosis of 7.3 years (interquartile range, 5.2-11.0 years). In the 60-70, 65-75, and 70-80 year old groups, SBP and incident dementia associations were not U-shaped, but rather approached an inverse linear relationship (i.e., the higher the BP, the lower the dementia risk). For older age groups (i.e., 75-85, 80-90 years old), associations were more U-shaped, with SBP of 170 mm Hg (95% confidence interval [CI], 160-260) and 158 mm Hg (95% CI, 152-178) associated with the lowest dementia risk in those two groups, respectively. Associations for diastolic BP (DBP) with dementia risk were similar.
In contrast, U-shaped associations were seen between SBP and both mortality and combined dementia and mortality across all age groups. The optimal SBP for mortality did vary with age, increasing from 134 mm Hg (95% CI, 102-149 mm Hg) in the youngest group (60-70 year olds) to 160 mm Hg (95% CI, 154-220) for those >90 years old.
Conclusions:
First, in the “younger” groups (e.g., 60-70, 65-75, and 70-80 years old), incident dementia and baseline SBP and DBP were inversely related, while in older age groups, more “U-shaped” associations were seen. Second, in contrast, both mortality and the combined outcome of mortality and dementia had clearly U-shaped associations with SBP, with the lowest risk SBP gradually increasing from the 130s in the youngest group to the 160s in those >75 years old.
Perspective:
Previous reports suggest that mid-life hypertension has been associated with a 60% increased risk of dementia. However, later in life this association may disappear, and some studies have shown association of hypertension and decreased risk of dementia.
This analysis of seven observational cohort studies paints an even more complex picture, with distinct patterns of association between SBP and dementia amongst differing age groups, including a nearly linear inverse relationship in patients below age 75 years. Any pretense of a “protective” effect of hypertension, however, is mitigated by the finding of a U-shaped association between SBP and the combined outcome of mortality and dementia.
Of course, the observational nature of these data prevent conclusions regarding causality, and the one-time assessment of BP and covariates fails to account for subsequent changes in these variables (e.g., prescription of new antihypertensive medications). Nonetheless, the results raise questions about the potential harm of low BP in elderly patients and previous randomized controlled trial (RCT) evidence that BP control reduces dementia risk. Future RCTs may be needed to test optimal strategies of BP control in elderly patients.
Clinical Topics: Cardiovascular Care Team, Geriatric Cardiology, Prevention, Hypertension, Smoking, Sleep Apnea
Keywords: Antihypertensive Agents, Blood Pressure, Body Mass Index, Cognition, Comorbidity, Dementia, Diabetes Mellitus, Geriatrics, Hypertension, Myocardial Infarction, Polypharmacy, Primary Prevention, Risk, Smoking, Stroke
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