A widely-prescribed drug to tackle high blood pressure and heart disease also appears to reduce the risk of Alzheimer's and other forms of dementia, according to a large US study published on Wednesday.
US military veterans who took angiotensin receptor blockers (ARBs) were between 19 and 24 percent less likely to develop dementia over a four-year period compared with counterparts who took other drugs, it said.
Among patients who were diagnosed with Alzheimer's at the start of the four years, those who took ARBs were nearly half as likely to be needing admission to a nursing home by the end, according to the research, published online by the British Medical Journal (BMJ).
ARBs block angiotensin, a molecule that causes the muscles in blood vessels to contract. As a result of the drug's action, the vessels dilate, easing blood pressure.
Previous studies have already suggested that ARBs are more effective at protecting against diabetes and possibly stroke when compared with other drugs.
But, say the investigators, this is the first demonstration of them as a bulwark against dementia.
Doctors led by Benjamin Wolozin, a professor at Boston University School of Medicine, looked at incidence of dementia among 819,000 people aged 65 or more with cardiovascular disease, most of them men, from 2002 and 2006. The data was provided by the US Veteran Affairs agency.
The patients were assessed according to whether they took ARBs; a cardiovascular drug called lisinopril; and other comparative drugs for treating heart disease.
ARB's apparent protection against dementia was found to be especially pronounced among men who used that drug in conjunction with another treatment for high blood pressure called angiotensin converting enzyme (ACE) inhibitors.
In a commentary also published by the BMJ, Colleen Maxwell and David Hogan of the University of Calgary, Canada, said the study had its limitations.
It did not factor in family history of dementia; was rather short in duration; and did not look at dementia among women.
Further work was needed to confirm the findings, they said.
Given that around 36 million people worldwide have a form of dementia such as Alzheimer's disease -- a tally that could double over the next 20 years -- the benefits of preventing this disease "are immense," they said.
Age, genetic inheritance and heart disease are established factors in dementia, to which diabetes and high blood pressure in mid-life have been tentatively added.
Explore further: 11th Sierra Leonean doctor dies from Ebola