Brain scans may identify early signs of Alzheimer’s disease even when there are no symptoms, a study has shown.

Researchers looked at more than 300 people in their 70s and 80s who had no memory or thinking pro-blems. A third of participants had significantly high levels of protein deposits linked to Alzheimer’s in their brains, the scans revealed.

Those with the accumulated proteins, called amyloid-beta plaques, also had abnormal levels of metabolic brain chemicals associated with mental decline.

The findings were published online in the journal Neurology.

Lead researcher Dr Kejal Kantarci, from the Mayo Clinic in Rochester, US, said: “This relationship between amyloid-beta deposits and these metabolic changes in the brain are evidence that some of these people may be in the earliest stages of the disease.

“More research is needed that follows people over a period of years to determine which of these individuals will actually develop the disease and what the relationship is between the amyloid deposits and the metabolites.”

Jonathan Schott, from the Dementia Research Centre, University College London, who wrote an editorial accompanying the research, said: “There is increasing evidence that Alzheimer’s disease is associated with changes in the brain that start many years before symptoms develop.

“If we could identify people in whom the disease process has started but symptoms have not yet developed, we would have a potential window of opportunity for new treatments – as and when they become available – to prevent or delay the start of memory loss and cognitive decline.”

An estimated 750,000 people in the UK suffer from dementia, 62 per cent of whom have Alzheimer’s.

The scientists used PET scans to assess amyloid-beta plaques and an advanced technique called proton MR spectroscopy to search for brain metabolites.