High Blood Pressure and Cognitive Decline in Mild Cognitive Impairment

There is controversy as to whether hypertension is a risk factor for cognitive impairment and decline, with some studies finding a positive association1–7 and others not.8–12 recent evidence-based review13 of published studies conducted by an expert panel under the auspices of the National Institutes of Health (NIH) concluded that the evidence of such an association is weak, in part because of the heterogeneity in definitions of mild cognitive impairment (MCI) and hypertension and differences in hypertension ascertainment methods (e.g., measured blood pressure (BP) vs reliance on self-report). In the United States, nearly 70% of persons aged 60 and older have hypertension,14 and it is estimated that 15 million to 18 million persons in this age group will develop dementia by 2050.15 Therefore, determining whether an association exists between high BP and cognitive function is important for targeting potential neuroprotective strategies. The results of clinical drug trials with antihypertensive agents have been mixed concerning their efficacy in preventing cognitive decline and dementia onset,13,16 although encouraging findings are available from a recent clinical trial employing lifestyle changes. One study17 found that prehypertensive and hypertensive adults receiving treatment with diet and aerobic exercise over a 4-month period showed greater improvements in executive functioning, memory, and psychomotor speed than those exposed to a diet intervention alone or a placebo condition of standard care. Systolic and diastolic BP decreased significantly over the study period for the intervention group but not the control group. The current study examined whether there is an association between high BP and decline in cognitive status in individuals with MCI over a 2-year period. The importance of the effect of adequate BP control on cognitive performance was demonstrated in a cross-sectional study of communityresiding older adults.18 Irrespective of a prior diagnosis of hypertension, persons with high BP (systolic ≥ 140 mmHg or diastolic ≥ 90 mmHg) at the time of neuropsychological testing performed worse than normotensive individuals on measures of visual memory, motor speed, and visuomotor integration. Persons with a prior diagnosis and high BP levels were most vulnerable to poor performance. BP levels were examined at annual follow-up visits, rather than at a single baseline visit, to determine whether BP was routinely normotensive or high and whether this, in turn, affected the trajectory of cognitive changes. Rather than a single measure of overall cognitive status, participants in the current study underwent multiple tests examining attention, memory, language, and executive functioning. In older adults without dementia and those with MCI and Alzheimer's disease, hypertension is associated with a cognitive phenotype characterized by poorer attention and executive functioning and slower processing speed.10,19–25 Thus, it was expected that these same areas would be most sensitive to the chronic effects of high BP. Information was collected as part of the Uniform Data Set (UDS), a standardized assessment and data protocol maintained by the National Alzheimer's Coordinating Center, with 31 participating NIH, National Institute on Aging (NIA) Alzheimer's Disease Centers (ADCs) nationwide.26,27 It was hypothesized that individuals with MCI with high BP readings, according to published guidelines for hypertension,28 on more than one occasion would exhibit faster overall cognitive decline than those with normotensive levels on all occasions, with greater vulnerability of attention, executive functioning, and speeded performance.