In the past, research into the relationship between blood pressure and cognitive impairment has yielded a wide range of results—some studies found that low blood pressure was linked with memory and processing problems, others that high blood pressure was associated with these risks, and others found no correlation at all. In an attempt to home in on more conclusive results, a team of researchers analyzed data collected for the Reasons for Geographic and Racial Differences in Stroke study for more than 19,000 patients ages 45 and older—who had no history of stroke. After controlling for a range of factors—including sex, age, race, region of residence, history of smoking and others—they did find a consistent correlation between cognitive impairment and higher diastolic blood pressure, or the minimum pressure exerted on the walls of the arteries when the heart is resting. (Systolic blood pressure, for which there was no correlation found with cognitive impairment, is a measurement of the maximum pressure exerted on the arteries when the heart contracts.)
For every 10 point increase in the measurement of diastolic blood pressure, researchers saw a 7% increase in likelihood of cognitive problems. Authors of the study, published this week in the journal Neurology, suggest that the relationship between higher diastolic blood pressure and cognitive processing problems may have to do with decreasing size of certain small blood vessels in the brain, which previous research have shown to be strongly influenced by diastolic blood pressure specifically.
The authors of the study admit to certain limitations on the research—namely, due to the study’s design, it isn’t clear whether increased diastolic blood pressure is causing cognitive impairment, or if the two problems coincide for other reasons, including the possibility that memory and other processing problems may in fact be driving the incidence of higher blood pressure by effecting diet and weight.
Still, while the existing scientific literature on the association between high blood pressure and impaired cognition isn’t exactly conclusive at this point, this study does add to several previous analyses that found similar results with regards to diastolic blood pressure. What’s more, to confirm these findings, the researchers are planning a four-year follow up using the same data set. In the meantime, based on the current results, the authors hypothesize that higher diastolic blood pressure may speed up arteriosclerotic changes in the brain—or the loss of elasticity and thickening of arterial walls that causes decreased blood circulation, and as a result, can lead to cognitive impairment.