Statins, which have saved millions of people from heart disease, may have an additional role in protecting the brain from dementia, researchers say.

The so-called "wonder drugs", taken by more than four million people in Britain to lower cholesterol, are estimated to prevent about 10,000 deaths a year. Now a study has shown they halve the rate of dementia in people at high risk.

The findings are based on a study of 1,674 elderly Mexican-Americans in California who had conditions that typically lead to dementia, including diabetes, obesity, high blood pressure and high cholesterol. Mary Haan, a professor of epidemiology at the University of Michigan, who led the study, said: "The bottom line is that if a person takes statins over a course of about five to seven years, it reduces the risk of dementia by half."

Statins were established as the most effective preventive treatment against heart disease more than a decade ago and are considered so safe that one, simvastatin, is available without prescription in Britain. In May, the National Institute for Clinical Excellence recommended that a further 1.5 million people should be offered them.

Last year, Professor Roger Boyle, the Government's national director for heart disease, suggested that every man over 50 and woman over 60 could be offered a daily statin.

A study last year of the brains of 110 Americans who had donated their organs for research after their deaths found significantly fewer signs of the "plaques" (protein deposits) and "tangles" (twisted nerve fibres) – which are indicators of dementia – in those who had taken statins. The study, at Boston University, concluded that statins reduced the risk by as much as 79 per cent. A second study by the university, presented at a conference in Chicago yesterday, found people taking blood pressure-lowering drugs called angiotensin receptor blockers, were up to 40 per cent less likely to develop dementia. The new findings, published in Neurology, confirm the earlier studies of statins and add to the growing weight of evidence that they may play a crucial role in preventing dementia.

Professor Haan, who has studied the same group of high-risk patients for more than a decade, said the statins had a bigger effect than expected. "This showed that if you started using statins before dementia developed, you could prevent it in about half of cases," she said.

Of the 1,674 participants in the study, just over a quarter (452) took statins at some point and 130 developed dementia or cognitive impairment.

Professor Haan said it was not clear how statins worked but it was possible that they lowered high insulin levels that could cause Alzheimer's disease. "We aren't suggesting people should take statins for purposes other than what they are indicated for but hopefully this study will open the door to testing for dementia and other types of cognitive impairment."

Clive Ballard, director of research at the Alzheimer's Society, said: "The jury is still out on how effective they [statins] are but this study adds to evidence that they may have benefits. All drugs have some side effects though, so it's important to seek professional medical advice.

"One in three people over the age of 65 will die with dementia. A search for new treatments is crucial, yet dementia remains underfunded and under-recognised as a research priority."

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