New study finds few clinical trials of blood pressure lowering and cognition are not state-of-the-art
Randomized controlled trials (RCTs) are considered the gold standard for clinical research, including the effects of blood pressure lowering on cognitive functioning. However, clinical trials aiming to improve normal cognitive function and slow the progress of dementia have yielded disappointing results.
Statistically significant findings have not been observed in many trials, despite large samples and promising antihypertensive drugs. Other trials find associations between blood pressure lowering and improved cognition, but the effect sizes are modest and it is not clear that they are clinically important.
Merrill Elias, Prof. of Psychology at the University of Maine, and Rachael Torres and Adam Davey, both of the University of Delaware, have published a review in the American Journal of Hypertension that identifies reasons why RCTs may yield small effects and provide research models that will improve future trials.
Elias and colleagues argue that most of the trials performed for non-demented individuals are not state-of-the-art in their assessment of cognitive outcomes for several reasons: they use too few cognitive measures; the design of test batteries is not based on long-standing theories of cognitive ability; the trials are not conducted for sufficiently long periods of time; and measurement of cognition takes a backseat to other trial goals.
The researchers identified 12 published RCTs that met criteria for inclusion in the review. Except for studies of dementia, cognitive measures used were inconsistent across the trials and systematic, theory-based guidelines for selecting cognitive measures were absent.
To improve the assessment of cognition in RCTs, Elias and colleagues suggest that trials examine areas of cognition that are known to be affected by dementia, and use test batteries that examine multiple areas of cognition and contain multiple cognitive measures. They also advocate for longer trial periods and use of standard assessment criteria when the trial’s primary goal is to slow or delay the onset of dementia.
Potential arguments against these suggestions include the high cost of longer trials and burden associated with use of larger cognitive test batteries. Though these limitations exist, finding ways to prevent or reduce cognitive decline is extremely important, say the researchers, noting that the benefits greatly outweigh the costs.