THURSDAY, May 1 (HealthDay News) -- Depression in women and stroke in men are critical factors in the development of Alzheimer's disease, French researchers report.

They analyzed data from almost 7,000 people over the age of 65 in three French cities. None of them had dementia, but about 40 percent had mild cognitive impairment at the start of the study.

They were assessed two and four years later. Of those with mild cognitive impairment at the start of the study, just over 6.5 percent developed dementia over the next four years, about half had no change, and about one-third regained normal levels of cognitive ability.

People with depression, those taking anticholinergic drugs (which influence chemical signaling in the brain), and those with a variation in the ApoE gene (a known risk factor for dementia) were more likely to progress from mild cognitive impairment to dementia.

The researchers also found that risk factors varied according to gender. Men with mild cognitive impairment were more likely to be overweight, diabetic and to have had a stroke. Men who'd suffered a stroke were almost three times more likely to progress from mild cognitive impairment to dementia.

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 with depression were twice as likely to progress from mild cognitive impairment to dementia, while women unable to perform routine daily tasks (which would allow them to live without assistance) were 3.5 times more likely to progress to dementia.

Stroke was not a risk factor for women, even though both women and men had similar rates of stroke.

The study was published online in the Journal of Neurology Neurosurgery & Psychiatry.

More information

The U.S. National Institute on Aging has more about Alzheimer's disease.