The risks of developing Alzheimer's disease differ between the sexes, with stroke in men, and depression in women, critical factors, suggests research published ahead of print in the Journal of Neurology Neurosurgery and Psychiatry.
The French researchers base their findings on almost 7000 people over the age of 65, drawn from the general population in three French cities.
None had dementia, but around four out of 10 were deemed to have mildly impaired mental agility (mild cognitive impairment) at the start of the study.
Their progress was assessed two and four years later.
In all, just over 6.5% of those deemed to be cognitively impaired developed dementia over the next four years. In just over half, no change was seen.
Just over one in three reverted to normal levels of cognitive agility.
Progression from mild cognitive impairment to dementia was more likely among those who were depressed and who were taking anticholinergic drugs, which influence chemical signalling in the brain.
A variation in the ApoE gene, a known risk factor for dementia, was also more common among those whose mild cognitive impairment progressed.
But risk factors also differed between the sexes, the results showed.
Men with mild cognitive impairment were more likely to be overweight, diabetic, and to have had a stroke. Men who had had a stroke were almost three times as likely to progress.
Women with mild cognitive impairment were more likely to be in poorer general health, disabled, suffering from insomnia and to have a poor support network.
Women unable to perform routine daily tasks, which would allow them to live without assistance, were 3.5 times as likely to progress. And those who were depressed were twice as likely to do so.
Stroke was not a risk factor for women, despite a similar rate of occurrence in both sexes.