“Although observational studies report hypertension to be an important risk factor for dementia, the benefit of blood pressure lowering on dementia or cognitive impairment in clinical trials is modest and lower than the risk reduction for stroke,” wrote
A rich data set
To assess the relationship between lowering blood pressure and cognitive issues, the researchers performed a systemic search of randomized, clinical trials that compared blood pressure lowering via antihypertensive agents with a control, had at least 1 year of follow-up, included more than 1,000 participants, and reported on either dementia, cognitive impairment, cognitive decline, or a change in cognitive test scores as outcomes. Of the 14 studies deemed eligible, 12 reported either the incidence of dementia (n = 9) or a composite of dementia or cognitive impairment (n = 3) at follow-up and thus were included in the primary meta-analysis. The other two studies were used for secondary outcomes only.
The studies included 96,158 participants in total – 42.2% were women – and their mean age was 69 years. At baseline, participants’ mean systolic blood pressure was 154 mm Hg and their mean diastolic blood pressure was 83.3 mm Hg. The mean duration of follow-up was 49.24 months.
In the 12 trials that reported dementia or cognitive impairment, blood pressure lowering via antihypertensive agents, compared with control, was significantly associated with a reduction in those two outcomes (7.0% vs. 7.5% over a mean trial follow-up of 4.1 years; odds ratio, 0.93; 95% confidence interval, 0.88-0.98; absolute risk reduction, 0.39%; 95% CI, 0.09%-0.68%). Blood pressure lowering, compared with control, was also significantly associated with a reduction in cognitive decline (20.2% vs. 21.1% over a mean trial follow-up of 4.1 years; OR, 0.93; 95% CI, 0.88-0.99; ARR, 0.71%; 95% CI, 0.19%-1.2%) in the eight trials that reported it as an outcome. An analysis of the eight trials that reported a change in cognitive scores did not find a significant association between that outcome and blood pressure lowering.
Subpopulations should be examined
“This is a very broad brush stroke study, albeit a definitive one,”, of the Mayo Clinic in Phoenix said in an interview. “With all the thousands of people in this meta-analysis, there are going to be subpopulations of patients with certain characteristics or common conditions in which blood pressure lowering might have a bigger or a lesser impact on their risk factor. Is there a difference between certain racial groups? Does it matter what antihypertensive strategies are used? You can look at the interactions between blood pressure lowering and other conditions: diabetes, head injuries, air pollution, certain genetic risk factors. There are a number of additional findings that could come from a very rich data set like this.”
The authors acknowledged their study’s limitations, including the challenges of performing a meta-analysis of studies that drew from different populations and had potentially different definitions of dementia, cognitive impairment, and cognitive decline outcomes. In addition, the low incidence of dementia across clinical trials limited the researchers, and its underdetection in trials and the potential of survivor bias for healthier participants with blood pressure reductions were noted as “unmeasured sources of potential error.”
Three authors reported receiving grants or personal fees from the Wellcome Trust and the Health Research Board, the Chief Scientist Office, and Bayer AG, respectively.
SOURCE: Hughes D et al. JAMA. 2020 May 19. .