By Kathleen Doheny
On the other hand, researchers linked high blood pressure in later life with greater risk of brain lesions for people who didn't have high blood pressure in their middle years. Brain lesions indicate damage and boost stroke risk.
"Our findings bring new insight into the relationship between a history of high blood pressure, blood pressure in old age, the effects of blood pressure on brain structure, and memory and thinking," said study researcher Lenore Launer, chief of neuroepidemiology at the U.S. National Institute on Aging.
History of high blood pressure appears to be the critical element in the link between blood pressure in old age and brain function, according to the study, published online June 4 in Neurology. It is also important to note that the research reveals links, not cause-and-effect relationships, between blood pressure levels, brain changes, and memory and thinking.
The research suggests two take-home points, said Dr. Gary Kennedy, director of geriatric psychiatry at Montefiore Medical Center in New York City.
First, those who develop high blood pressure later in life can benefit from treatment, said Kennedy, who was not involved in the study. Second, those with high blood pressure in midlife who take medication to lower it should keep monitoring blood pressure in later life, he said. If the pressure becomes low, this study suggests it might put you at risk of dementia, he said.
The study didn't look at the mechanism, but Kennedy suspects the thinking and memory problems linked with lower blood pressure in old age may be linked with a decline in oxygen to the brain.
However, Kennedy cautioned against simply stopping your blood pressure medicine. "Check with your doctor," he said.
For the study, researchers measured the blood pressure of more than 4,000 adults in middle age, aged 50 on average. All were dementia-free at that time. The men and women had blood pressure measured again, at 76 years on average. At that time, MRIs assessed any damage to small blood vessels in the brain. The researchers also tested memory and thinking skills.
It's known that the relationship between blood pressure levels at middle age and later brain problems, including dementia, is complicated, Launer said.
Blood pressure levels tend to decline with age, and also decline when people experience dementia. Launer's team decided to look at midlife blood pressure and track the effects of both high and low blood pressure on the brain.
The researchers found that those who had high blood pressure in middle age but low diastolic pressure -- the bottom of the two readings -- in later life had brain shrinkage. They scored 10 percent lower on memory tests.
Meanwhile, those without high blood pressure in midlife who had high diastolic pressure in later life were 50 percent more likely to have severe brain lesions than those with low diastolic pressures.
Diastolic pressure measures pressure in the arteries between heartbeats. Systolic pressure, the top number, measures pressure when the heart beats. Blood pressure readings at or below 120 over 80 millimeters of mercury (mm Hg) are viewed as normal.
Experts suggest treatment with medication when blood pressure reaches 140/90 mm Hg. An expert panel last year recommended looser guidelines for most people age 60-plus, suggesting medication not be prescribed until readings reach 150/90 mm Hg.