Scientists from Stockholm have developed a list of warning signs for the onset of Alzheimer's disease (AD).
Lead by Dr Lars Backman, from the Karolinska Institute, the team analysed 47 studies involving 1, 207 people who developed the disease and 9,097 who stayed healthy.
They then identified a number of symptoms that preceded an onset of later Alzheimer's.
The symptoms were similar to those present in normal ageing, but they were more pronounced.
They included, gradual loss of mental ability, memory, perceptual speed, verbal ability and attention.
Dr Backman said the fact that there is no qualitative difference in cognitive patterns between the normal 75-year-old and the preclinical Alzheimer's disease patient means medical staff will have challenges accurately diagnosing early AD.
"Rather, we think of the normal elderly person, the preclinical AD person, and the early clinical AD patient as representing three instances on a continuum of cognitive capabilities," Dr Backman said.
The study found that preclinical symptoms, such as impairment, were the worst in patients who developed the disease young and progressed quickly.