In a study involving more than 500 participants 90 and older, UC Irvine researchers say the onset of high blood pressure at a late age is associated with a lower risk of dementia after age 90.
The study — published online Tuesday in Alzheimer's & Dementia: The Journal of the Alzheimer's Assn. — indicated the risk is even lower if hypertension is developed at 80 or older, researchers said.
"In terms of hypertension, that was not necessarily what we were initially expecting when we started our study," said Maria Corrada, a UCI professor of neurology and epidemiology and first author of the study. "Hypertension is bad in the young, midlife or elderly. But what we're seeing is that if it's developed in later life, that may be a good thing for them."
Participants in the study did not have dementia when they enrolled. Corrada and the research team followed some of the subjects for as long as 10 years.
Participants received dementia assessments every six months during the study, which began in 2003. Researchers said 224, or 40%, of the participants were eventually diagnosed with dementia.
Those who began to develop hypertension in their 80s were 42% less likely to develop dementia after age 90, compared with those who had no high blood pressure, according to the findings.
Those who began to experience hypertension at 90 or older were 63% less likely to develop dementia, the study indicated.
"It's not saying that everybody who developed it later on didn't get dementia," Corrada said. "But on average, people who developed it at a higher age were less likely to develop dementia."
Corrada said the team has not concluded anything and that the study simply points out the observation.
Though studies of the relationship between hypertension and dementia have been done before, "this paper is the first publication we've had that looks at this particular population [people in their 90s], and what they're seeing in the 'oldest old' is not what we've seen in other studies," said Heather Snyder, senior doctor of medical and scientific operations at the Chicago-based Alzheimer's Assn.
"What's bad for you in midlife might not be bad for you in later life," Snyder said. "But we have to think about what that means in the underlying biology and what we can apply to future understanding."
As for why late-age hypertension onset seemingly reduces the risk of dementia, UCI researchers have a few possibilities they're looking into, Corrada said.
"We believe that it may be because blood vessels become stiffer with age [and] a high blood pressure is needed to pump blood to the brain," she said. "We've been under the impression that hypertension is a bad thing, no matter what. I'm always trained to be skeptical but to also try and find a possible explanation for what's being found."