People who self-reported worsening memory were three times as likely as others to develop cognitive problems later on in life, which can be a precursor to dementia, the US study found.
The most notable finding, however, was that it took at least nine years for cognitive impairment and 12 years for dementia to occur after these memory changes began.
Researchers from the University of Kentucky said this may give clinicians a window of opportunity to intervene before the disease is formally diagnosed.
In the study, published in the journal Neurology, 531 volunteers, aged on average 73 years and without dementia, were asked annually for 10 years whether they had experienced any recent changes in their memory. They also had memory and thinking tests each year.
The researchers found that 56% of participants self-reported memory changes in this time, and these people were three times as likely to develop cognitive impairment, on average 9.2 years later.
About one in six people in the study developed dementia, 80% of whom had reported memory problems an average of 12.1 years beforehand.
Smokers who reported memory problems developed impairment more rapidly than non-smokers, while women taking HRT took longer to develop dementia. Autopsies of 243 patients in the cohort who died revealed that even those with memory problems who did not develop clinical impairment displayed higher levels of Alzheimer-type disease in the brain.
Study author Richard Kryscio PhD from the University of Kentucky said: ‘Our study adds strong evidence to the idea that memory complaints are common in older adults and are sometimes indicators of future problems. Doctors should not minimise these complaints and should take them seriously.
‘However, memory complaints are not a cause for immediate alarm, since impairment could be many years away. And unfortunately, we do not yet have preventive therapies for Alzheimer’s disease and other illnesses that cause memory problems.’
Dr Simon Ridley, head of research at Alzheimer’s Research UK, said: 'Many people will experience a decline in memory as they age, and this single study adds to evidence showing that some people who experience mild memory loss in older age go on to develop dementia.
'Although we all forget things from time to time, memory loss in dementia is more severe than occasional bouts of forgetfulness, and it’s important to note that many people who report mild memory problems do not develop the condition.'