While a link between blood pressure and dementia has been observed for some time, today’s finding — that lowering your systolic blood pressure to 120 reduces dementia risk by 15 percent — represents a major advance as the first randomized clinical trial to measure the direct effect.
The research follows news-making European dementia studies published this year that showed how even mild high blood pressure at age 50 might contribute to dementia in your 70s. Those studies, however, did not test what lowering systolic pressure to 120 might do in a specific audience versus a control group.
"For many years there has been observational evidence that these two were linked — but observation and causation are two different things," said the study’s lead author, Jeff D. Williamson, M.D., chief of geriatrics and gerontology at the Wake Forest School of Medicine. Not only did his research show a causal link, but it did so after an average of four to five years of having participants maintain an upper blood pressure reading of 120. "This is very encouraging because it means you don't have to maintain the lower systolic pressure for a very long time to see that reduction in risk," he says.
What’s also encouraging? That the lower blood pressure threshold had a direct effect on the very earliest stage of the disease, reducing mild cognitive impairment (MCI) by 19 percent. "MCI is the earlier stage, one that for most people is even more important because it’s the gateway to dementia or even Alzheimer’s disease," Williamson explains. "If you can stop it early, you can make the biggest impact."
The results come out of the same study that late last year led the American Heart Association to suggest lower systolic blood pressure guidelines for everyone, from below 140 to below 120. Called the Systolic Blood Pressure Intervention Trial Study, or SPRINT, the three-pronged clinical trial sponsored by the National Institutes of Health National Heart, Lung, and Blood Insitute tested 9,361 participants according to how the tougher-to-meet blood pressure target affected their hearts, kidneys and brains.
Participants were split into two groups, with one maintaining a systolic blood pressure of 140 and the other receiving medication — as well as diet and exercise advice — that lowered their systolic blood pressure to 120. To measure the effect on dementia, participants took periodic cognitive tests and were examined and interviewed by a panel of experts that included neurologists, geriatricians and others. A separate research group affiliated with the University of Pennsylvania took brain scans.
As for the factors that might be behind the finding, Williamson explains that, if left untreated, higher blood pressure could create stress on the arteries that changes the walls of blood vessels, which in turn could cause inflammation of the brain that leads to dementia. He also points to the University of Pennsylvania–sponsored research, also released at today’s conference, which linked the lower blood pressure target to the production of less cerebral white matter, another biomarker for dementia.