Abstract
Introduction:
While elevated systolic blood pressure (BP) is a known contributor to cognitive decline, the role of elevated diastolic BP (DBP) as an independent risk factor for cognitive decline is less clear, especially in relationship to systolic BP (SBP) levels.
Objectives:
To characterize the association between DBP and cognitive functioning at differing levels of SBP.
Methods:
The National Health and Nutrition Examination Survey is a nationally representative survey of U.S. adults conducted annually. Our sample included data from participants of the 1999-2002 and 2011-2014 cycles, age 60+, with measured BP and cognition (N=5,480). BP was measured three times manually with a standardized sphygmomanometer and averaged. Cognitive functioning was measured using the digit symbol substitution test (DSST), a measure of executive functioning (with higher scores indicating better performance: range 0-100). We tested for a statistical interaction between SBP and DBP. To determine whether DBP was associated with DSST score, we used linear regression analyses and stratified by categories of SBP. Models were adjusted for: age, sex, race, education, income, insurance, marital status, BMI, diabetes, BP medication, and cholesterol. All analyses accounted for the complex survey design.
Results:
Almost half (48.9%, SE=1.1) of the sample was aged 60-69 with 55.3% (SE=0.7) female. The association between DBP and cognitive functioning differed by SBP (p<0.01), leading to stratified analyses. Every 5 mmHg increment of DBP was associated with significantly higher DSST scores among individuals with SBP 110-119 mmHg only (beta: 0.76, 95% CI: 0.24, 1.27). Results were not significant among participants with SBP < 110mmHg (beta: 0.84, 95% CI: -0.09, 1.77), SBP 120-129 mmHg (beta: 0.09, 95% CI:-0.49, 0.69), SBP 130-140 mmHg (beta: 0.29, 95% CI: -0.10, 0.69), SBP 140-159 mmHg (beta: 0.23, 95% CI: -0.15, 0.61), or SBP ≥160mmHg (beta: -0.08, 95% CI: -0.56, 0.39).
Conclusion:
In a population-based sample of older US adults, higher DBP was associated with greater executive functioning only among individuals with normal SBP. The results suggest that at non-hypertensive levels of SBP, higher DBP may not be detrimental for cognitive performance.
