Researchers have devised a memory test for predicting Alzheimer's disease nearly two decades before it fully develops, proving that symptoms for the debilitating condition may show up much earlier than previously thought.

"The changes in thinking and memory that precede obvious symptoms of Alzheimer's disease begin decades before," said study author Kumar B. Rajan in a statement. "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."

For the study, 2,125 European-American and African-American people over the age of 65 who did not have Alzheimer's disease at the start of the research were given a simple memory test every three years for 18 years. Twenty-three percent of African-Americans and 17 percent of European-Americans ended up developing Alzheimer's disease during the study.

Researchers found that people who scored lower on the test in just the first year were 10 times more likely to be diagnosed with the disease than people with higher scores. In fact, the odds of eventually being diagnosed increased by 10 for every standard deviation that the score was lower than the average.

Furthermore, one unit lower in performance of the standardized cognitive test score was associated with an 85 percent greater risk based on tests completed 13 to 18 years before the final assessments took place.

"A general current concept is that in development of Alzheimer's disease, certain physical and biologic changes precede memory and thinking impairment. 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," Rajan explained.

It should be noted that a lower than average score on the test did not indicate with 100 percent certainty that Alzheimer's would eventually develop; a low score merely increases the likelihood that it will. Even so, the test could prove to be a valuable tool in preparing, treating and possibly even preventing or forestalling future dementia.

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