People whose brains seem to be very healthy may still be in the process of developing Alzheimer's disease, according to recent US research.

The researchers found that 22% of the people they studied whose minds were in good health had signs of what they call preclinical Alzheimer's disease.

John Morris, director of the Alzheimer's Disease Research Center at Washington University in the US, said that his team's finding was the first evidence that perfectly healthy people can have amyloid plaques.

Amyloid plaques are one of the telltale signs of Alzheimer's disease.

They are implicated in the protein twisting that goes on at a molecular level in the brain of Alzheimer's sufferers, putting people who have them at very high risk of developing symptoms of Alzheimer's disease over a three- to four-year period.

For the purposes of the study, the research team assembled 135 subjects whose ages ranged between 65 and 88.

Though all of the subjects had highly attuned mental functioning, more than a fifth of them had amyloid plaque deposits.

In a follow-up study, Morris and his colleagues tested 159 more people with an average age of 71.

In the second group of subjects, those who had already developed amyloid plaque deposits were almost five times more likely to develop mild symptoms of dementia than the general population.

Gary Kennedy, director of geriatric psychiatry at Montefiore Medical Center in New York, who was not involved in the study, said that he felt the research was important.

He said that dementia researchers wanted to identify people at risk of developing Alzheimer's in the hope that they could find ways to slow the progress of the disease and limit its impact.

Morris said that doctors were currently unable to treat Alzheimer's disease at all, and that they should clarify, refine, and define their clinical detection of the disease.

He said that researchers in his field would like to combine early detection with preventive measures.

In the course of their research, Morris and his colleagues encountered a man whose brain did not show signs of amyloid plaques at all, but who went on to develop Alzheimer's.

Kennedy said that the fact that the man's brain did not have the plaques gave him hope because it meant that Alzheimer's might be more akin to a family of related, treatable symptoms than to a single unbeatable condition.

Morris said that he believed doctors could expect a day when they could predict people's risk of developing dementia 10 or 20 years later.