Web desk: (courtesy Web MD) Developing high blood pressure in very old age may provide some protection from dementia, a new study suggests.

In middle age,high blood pressure also called hypertension — boosts dementia risk later in life, said study lead researcher Maria Corrada. It also raises your risk for heart attack and stroke

But its onset in the eighth or ninth decade of life was linked to lower risk of mental decline in one’s 90s, her team found.

“Hypertension in the very old is not detrimental for mental health,” said Corrada, a professor of neurology and epidemiology at the University of California, Irvine.

Several factors may help explain the apparent association between late-life high blood pressure and lower dementia risk, Corrada said.

For one, as people age,  blood pressure may need to increase to keep blood flowing to the brain  for normal functioning.

“It’s a matter of creating enough pressure to get blood to oxygenate the brain adequately,” Corrada said.

The researchers said it’s also possible, but less likely, that blood pressure drops as dementia begins due to the deterioration of brain cells. This could mean that elderly people who don’t develop dementia will have higher blood pressure.

High blood pressure in the very old might have other benefits, Corrada said. “There is evidence that high blood pressure may also reduce frailty and disability,” she said.

It’s clear that age matters, Corrada said, although the study didn’t prove a cause-and-effect link between high blood pressure and reduced dementia risk.

“Whatever we know and learn about the health of the younger elderly does not necessarily apply to the health of the ‘oldest old’ — the fastest-growing segment of the population,” she said.

To avert a public health epidemic of dementia, it’s important to understand how risk for mental decline might change over time, the researchers and others said.

High blood pressure may need to be divided into at least two classes, said Dr. Sam Gandy, a New York City brain specialist.

“We usually think of the young adult onset form, which if untreated can damage heart, kidney, eye and brain blood vessels,” said Gandy, director of the Center for Cognitive Health at Mount Sinai Hospital in New York City.