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And dementia patients who were newly started on the drugs had, on average, a small improvement in the first six months.
The drugs linked to the benefit are known as centrally acting ACE inhibitors, which means they cross from the blood into the brain. They include commonly used medications such as captopril (Capoten), fosinopril (Monopril), lisinopril (Prinivil or Zestril), perindopril (Aceon), ramipril (Altace) and trandolapril (Mavik).
The study was not a clinical trial set up to test the effects of ACE inhibitors, noted Dr. Gayatri Devi, of Lenox Hill Hospital in New York City.
Instead, she said, it was an "observational" study, where researchers followed more than 350 older adults with Alzheimer's or other forms of dementia -- about one-quarter of whom happened to be on ACE inhibitors. Those types of studies cannot prove that a drug is the reason for a particular benefit.
"And there are past studies that have contradicted this one, and have not shown a benefit of ACE inhibitors," Devi said.
On the other hand, the findings support the "larger message" that better cardiovascular health -- including controlling blood pressure and cholesterol levels -- can benefit the brain as well, she said.
Previous studies have linked better blood pressure control -- and various classes of blood pressure drugs -- to both a lower risk of developing dementia and a slower progression of the disease. Currently, no treatments exist to prevent or modify dementia.
"The blood pressure medication that's best for you is the one that most effectively controls your blood pressure," Devi said. "People respond differently to the different classes of blood pressure drugs."
The study included 361 dementia patients, average age 77, who completed standard tests of memory, planning and other mental abilities. Of those, 85 were already on a centrally acting ACE inhibitor, and 30 more started on one during the study period.
On average, test scores declined by 1.8 points every six months among patients who were already on ACE inhibitors. That compared with 2.1 points for patients not on the drugs.
Among patients who newly started an ACE inhibitor, test scores typically rose 1.2 points in the first six months -- which was as long as that group was followed. The rest of the study patients were tracked for about a year-and-a-half.
Those are small differences in test scores. But if they persisted over years, that could add up to a significant difference in dementia patients' rate of decline, said Dr. William Molloy, one of the researchers on the study.
Clinical trials are needed to confirm whether certain ACE inhibitors do, in fact, slow down dementia, according to Molloy, a professor of gerontology and rehabilitation at University College Cork in Ireland.
He said he does not think the benefit linked to ACE inhibitors is explained by better blood pressure control. There is animal research showing that ACE inhibitors that cross into the brain may have a stronger effect on brain functioning than ACE inhibitors that do not breach the blood-brain barrier.
One possibility, Molloy said, is that the drugs reduce inflammation in the brain.
But another expert not involved in the study urged caution. "I don't think these findings should be used in any clinical decision-making," said Dr. Jacobo Mintzer, chair of the Alzheimer's Foundation of America's medical advisory board.
"This study supports the general concept that controlling blood pressure and other cardiovascular risk factors could have an effect" on dementia progression, said Mintzer, of Roper St. Francis Healthcare in Charleston, S.C.
But he agreed with Devi that the specific medication you take for high blood pressure should be the one -- or ones -- that best rein in your numbers.
The study was funded by government and private grants; none of the researchers reports any financial conflicts of interest.
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