High blood pressure can be a warning of ill health
Controlling blood pressure from middle-age onwards may dramatically reduce the chances of developing dementia, researchers have said.
Two studies support a link between high blood pressure and dementia risk - with one by an Imperial College London team suggesting treatment could cut this.
This study, by published in the Lancet Neurology journal, found blood pressure drugs reduce dementia by 13%.
The Alzheimer's Society said better control could save 15,000 lives a year.
As many as one in four people has high blood pressure, in many cases undiagnosed or untreated.
The precise reasons why high blood pressure might increase the risk of dementia are not fully understood although many scientists believe that it can starve the brain of bloodflow and the oxygen it carries.
Patients suffering this restricted bloodflow are often described as having "vascular dementia", and account for approximately a quarter of dementia patients.
Other types of dementia, such as Alzheimer's disease, have no obvious link to bloodflow, but some experts think that blood pressure may still be somehow contributory in some cases.
The Lancet Neurology study looked at a trial of elderly patients with high blood pressure to see if those who were receiving treatment were less likely to develop any form of dementia compared with those left untreated.
The trial was stopped early after the benefits of treatment in terms of reducing strokes and heart disease were so obvious it became unethical to deny them to everyone.
Although this meant that no benefits in terms of dementia could be found, when these results were combined with other similar studies in different age groups, the incidence of dementia was 13% lower in the treated groups.
Dr Ingmar Skoog, from the Institute of Neurosciences at Sweden's Goteburg University, said that the need to treat high blood pressure, reducing heart attacks and strokes, was clear, even without the additional results on dementia.
Rebecca Wood, from the Alzheimer's Research Trust, said the finding was an "exciting development", which, if repeated, could offer hope to the 700,000 people in the UK with dementia.
The Alzheimer's Society, however, stressed the need to try to prevent the disease.
Its own unpublished research suggested that vascular dementia was six times more likely to develop in people who had high blood pressure in their 40s and 50s.
If "best practice" in blood pressure treatment was applied to the UK population, it said, with every case detected and treated appropriately, this would save 15,000 lives a year.
Professor Clive Ballard, its director of research, said: "Only half of people over 65 receive effective treatment, yet we know treatment works."
The charity's chief executive, Neil Hunt, urged everyone, even those in middle age, to have regular blood pressure and cholesterol checks.