When healthy patients score less on memory tests, it may be a warning for future development of Alzheimer's disease.
"The changes in thinking and memory that precede obvious symptoms of Alzheimer's disease begin decades before," said, study author Kumar Rajan, of Rush University Medical Center in Chicago.
More than 2,000 people with an average age of 73 participated in the experiment. None of the participants were diagnosed with Alzheimer's at the start of the study and the memory tests, which included thinking skills, were given every three years for nearly two decades.
"While we cannot currently detect such changes in individuals at risk, we were able to observe them among a group of individuals who eventually developed dementia due to Alzheimer's," said Rajan.
Those who had scored lowest on the tests throughout the study were at greater risk for developing the disease; 23% of the black individuals and 17% of the white developed Alzheimer's during the study period.
The research indicated that after the first year, those scoring lower on the tests were about 10 times more likely to develop the disease than those with the best scores. And as the scores dropped below average, odds for the disease increased.
"A general current concept is that in development of Alzheimer's disease, certain physical and biologic changes precede memory and thinking impairment," said Rajan. "If this is so, then these underlying processes may have a very long duration. Efforts to successfully prevent the disease may well require a better understanding of these processes near middle age."