A study of over 2000 people published in Neurology has shown that a test of memory and thinking can reveal differences in people who would go on to develop Alzheimer's disease up to 18 years before diagnosis.
Based on tests completed 13 to 18 years before the final assessments took place, one unit lower in performance of the cognitive test score was associated with an 85 per cent greater risk of future dementia.
This suggests that the preclinical phase of Alzheimer's disease may begin many years earlier than expected.
Dr Doug Brown, Director of Research and Development at Alzheimer's Society, said:
'Dementia often causes changes in the brain years before the symptoms become apparent. This study shows that there may be subtle indications of Alzheimer's disease in thinking and memory as many as 18 years before a formal diagnosis could take place. This could mean there is a long window of opportunity for treatment in which we could one day halt or slow dementia.'
'Alzheimer's Society currently funds researchers to develop scientific and cognitive tests to identify changes in the brain linked to dementia in the early stages. Although these tests cannot accurately predict who will develop dementia, they could potentially be used to identify people at higher risk.'