Alzheimer's disease, a form of dementia, is the fifth leading cause of death for people aged 65 and over in the US.
"Our study adds strong evidence to the idea that memory complaints are common among older adults and are sometimes indicators of future memory and thinking problems. Doctors should not minimize these complaints and should take them seriously," says study author Richard Kryscio, from the University of Kentucky in Lexington.
Dementia is the name given to a group of cognitive disorders that commonly impair the memory, as well as language abilities, motor functions, object recognition, and decision making. In the majority of cases, these disorders are found to affect older adults.
The most common form of dementia is Alzheimer's disease, a progressive disease of the brain characterized by memory loss and impaired mental functioning. Around 5.3 million Americans currently have Alzheimer's disease and, due to an aging population, experts expect this figure to double by 2050.
Researchers from the University of Kentucky assessed the prevalence of subjective memory complaints over time in connection with the development of mild cognitive impairment and dementia. The study and its findings are published in the American Academy of Neurology's journal Neurology.
With an average age of 73, a total of 531 people took part in the study. The participants were all free of dementia at the beginning of the study and were asked every year if they had experienced any changes in their memory.
The participants also had to complete annual memory and thinking tests, for an average follow-up period of 10 years. The brains of 243 of the participants were examined after death for signs of Alzheimer's disease.
During the study, 56% of the participants reported experiencing changes in their memory at an average age of 82. Those who reported memory complaints were found to be nearly three times more likely to develop memory and thinking problems.
Around 1 in 6 participants were found to develop dementia over the duration of the study, with 80% of these participants reporting memory changes beforehand.
Perhaps the most significant finding was the interval between the initial reporting of a subjective memory complaint and the development of dementia or other cognitive impairment.
"What's notable about our study is the time it took for this transition to dementia or clinical impairment to occur - about 12 years for dementia and 9 years for clinical impairment - after the memory complaints began," says Kryscio. "These findings suggest that there may be a window for intervention before a diagnosable problem shows up."
'Not cause for immediate alarm'
The authors acknowledge that their study was limited by the fact that participants were only asked one simple question about subjective memory complaints at each yearly follow-up. Self-reporting from the participants may have also led to misclassification of memory complaints and other risk factors such as smoking and diabetes.
Despite these limitations, the authors are content to state that while memory complaints could indicate the future development of dementia, subjective memory complaints "are not cause for immediate alarm because impairments could be many years away."
Unfortunately, as Kryscio states, "we do not yet have preventive therapies for Alzheimer's disease and other illnesses that cause memory problems." Approved treatments aim to lessen the symptoms of the condition but are unable to prevent its progression.
Alzheimer's Disease International commissioned the World Alzheimer's Report 2014 as part of World Alzheimer's Month this September. Medical News Today recently revealed the key findings of the report, which claims that diabetes and high blood pressure should be targeted to reduce the risk of dementia.