Millions of older people who take drugs for high blood pressure or heart problems can more than halve their risk of developing Alzheimer’s disease and dementia, according to research.

Use of angiotensin receptor blockers (ARBs) is linked to a “striking decrease” in the chance of getting the condition or of it progressing, especially in men, says a study published in the British Medical Journal. The drugs play a key role in delaying the symptoms of dementia and so may reduce the number of people dying early or needing to enter a nursing home, the study finds.

Patients taking ARBs had up to a 50% lesser risk of getting dementia, the journal reports. While ARBs are only one of the types of drugs used to treat high blood pressure and cardiovascular disease, the research pinpoints their usefulness in tackling dementia. In 2008, a total of 14.5m doses of ARBs were prescribed to patients in England at a cost of £272m.

About 700,000 Britons have some form of dementia, and more than half have Alzheimer’s disease. The number of sufferers is predicted to rise to a million in the next decade and to 1.7 million by 2051. One in three Britons aged over 65 is likely to die of dementia.

Professor Benjamin Wolozin and colleagues at Boston University studied 819,491 people in the US aged over 65 who had heart disease, of whom 98% were men.

Alzheimer’s campaigners welcomed the findings. “We have known for a while that it is important to control blood pressure from mid-life to reduce the risk of developing dementia,” said Dr Susanne Sorensen, head of research at the Alzheimer’s Society. “The prospect of using already existing drugs to help in the fight against dementia is attractive.”

“This adds further weight to the adage that what is good for the heart is good for the head,” said Rebecca Wood, chief executive of the Alzheimer’s Research Trust. “It could be that ARBs protect brain cells from injury caused by damaged blood vessels.” Further trials were needed to see how far ARBs could help ward off the disease, Wood added.

Meanwhile, the loss of ability to smell could be an early warning sign of Alzheimer’s and prompt earlier diagnosis, separate research suggests. It is known that Alzheimer’s can lead to the loss of a sense of smell, although why that happens is unclear. A study in the Journal of Neuroscience, by American scientists working on mice, links the failing ability to smell to the buildup of amyloid, a toxic protein that is an indicator of the disease. Experts said the findings suggested loss of smell could be used as an early indicator of the condition and thus ultimately improve medical care.