Blood Pressure Control and Cognitive Performance

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JAMA

Something to Think About With Aging

May 19, 2015, Vol 313, No. 19 >

Along with declining memory performance, elevation of systolic blood pressure and an increased prevalence of hypertension are expected consequences of advancing age. It is not surprising, therefore, to expect that the two processes may be related. In 1987, Inzitari et al1 first identified brain injury and subtle cognitive impairment associated with elevated levels of systolic blood pressure (SBP). In 1995, Launer et al2found that elevations in middle-life blood pressure were associated with reduced cognitive function in later life. Many studies subsequently confirmed and extended research related to the relationships among middle-life blood pressure, brain injury, and cognitive function among community-living individuals, suggesting that the inverse relationship between middle-life blood pressure and reduced cognitive ability is nearly universal. Using a twin study design, Swan et al3 also confirmed the association between middle-life patterns of SBP and cognition and identified that the cognitive differences were likely mediated by brain injury related to the level of middle-life blood pressure.

This seemingly straightforward association between elevated SBP and reduced cognitive ability was challenged when a number of studies found that blood pressure appeared to decline years before the onset of dementia, that cross-sectional measures of blood pressure obtained later in life were not strongly associated with brain structure or cognition, and that treatment of elevated blood pressure in later life was not associated with reduced likelihood of incident dementia.4 The literature is further limited by the fact that hypertension prevalence is greater among nonwhite populations, and dementia is more prevalent in nonwhite populations, but much of the research on the relationship between hypertension and cognition is from white cohorts.

Charles DeCarli, MD1

Along with declining memory performance, elevation of systolic blood pressure and an increased prevalence of hypertension are expected consequences of advancing age. It is not surprising, therefore, to expect that the two processes may be related. In 1987, Inzitari et al1 first identified brain injury and subtle cognitive impairment associated with elevated levels of systolic blood pressure (SBP). In 1995, Launer et al2found that elevations in middle-life blood pressure were associated with reduced cognitive function in later life. Many studies subsequently confirmed and extended research related to the relationships among middle-life blood pressure, brain injury, and cognitive function among community-living individuals, suggesting that the inverse relationship between middle-life blood pressure and reduced cognitive ability is nearly universal. Using a twin study design, Swan et al3 also confirmed the association between middle-life patterns of SBP and cognition and identified that the cognitive differences were likely mediated by brain injury related to the level of middle-life blood pressure.

This seemingly straightforward association between elevated SBP and reduced cognitive ability was challenged when a number of studies found that blood pressure appeared to decline years before the onset of dementia, that cross-sectional measures of blood pressure obtained later in life were not strongly associated with brain structure or cognition, and that treatment of elevated blood pressure in later life was not associated with reduced likelihood of incident dementia.4 The literature is further limited by the fact that hypertension prevalence is greater among nonwhite populations, and dementia is more prevalent in nonwhite populations, but much of the research on the relationship between hypertension and cognition is from white cohorts.

The Atherosclerosis Risk in Communities (ARIC) project addresses many of these discrepancies in the literature. This project was designed to examine the association of vascular risk factors with general and cognitive health. The project was initiated in 1987 and recruited more than 15 000 individuals from 4 communities throughout the eastern and southern United States. When recruited, participants were aged 45 to 64 years, and approximately 30% of the study cohort was African American.

In a recent study in JAMA Neurology, Gottesman et al5 address the controversies of blood pressure regulation and cognition with a report on longitudinal differences in cognitive performance over 20 years in relation to baseline blood pressure measures among the participants of the ARIC cohort. In addition, the authors explored the effects that various definitions of blood pressure, medical illnesses commonly associated with hypertension, drop-out, and mortality also might have on the results.

Gottesman et al5 report a number of important observations. In this essentially healthy, community-based cohort who were, on average, 56 years old when baseline cognitive assessment was obtained, prehypertension or hypertension was present at baseline in 58% of white and 76% of African American study participants. Death was a major outcome related to having hypertension at the first evaluation, with fewer than 50% of individuals with SBP greater than 160 mm/Hg surviving to an average age of 76 years. Of those who survived and continued to participate in the study through the 5 visits over 20 years, there was a significant, albeit modest, association between baseline SBP and rate of cognitive decline, particularly in tasks mediated by attention, short-term memory, and retrieval. Moreover, when SBP was analyzed as a continuous measure, there was an inverse, linear relationship with rate of cognitive decline (ie, the higher the middle-life SBP, the greater the rate of decline). When adjusted for mortality, the effect size of hypertension on global cognitive performance was increased by nearly 70% (from −0.056 to −0.091 global cognitive z score units). The initial analyses excluded individuals who became demented over the course of the study, but secondary analyses that included demented individuals strengthened the relationship between SBP and rate of cognitive decline. Moreover, individuals receiving hypertension treatment had substantially slower rates of cognitive decline compared with those who were untreated, particularly among African American individuals. Consistent with other studies, there was no association between SBP level measured when patients were assessed at the 20-year follow-up and cognitive ability.

The authors conclude that lowering blood pressure is associated with reduced risk of negative cognitive consequences of hypertension and note that the duration of existing clinical trials may be too short to identify a subtle benefit of antihypertensive therapy on cognitive outcomes. However, as the authors further note, even subtle improvements in blood pressure control could have a large population effect that might further translate into reduced life-time risk for late-life dementia.

This study highlights the importance of blood pressure control but also emphasizes the need to begin treatment early in life. The proportion of people with hypertension receiving effective treatment is increasing.6 However, considerable numbers of people younger than 50 years who have hypertension are not getting diagnosed or treated appropriately. There needs to be greater awareness of the negative health effects of hypertension to younger patients as data from the Framingham Heart Study show that brain injury can occur before age 50 years7 from prehypertension and hypertension in addition to the cognitive findings found previously in ARIC.8 Treating hypertension in younger patients, therefore, will not only save lives but also improve the quality of life and may reduce dementia complications that occur later in life.

 

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