Researchers now say that women over their 90s are more likely to suffer from dementia than their male counterparts.
The team led by researchers from University of California, Irvin, studied 911 people enrolled in the 90+ Study.
They found that 45 percent of the women had dementia, compared to 28 percent of the men.
"Our findings show that more will need to be done to provide adequate resources to care for the increasing number of very old people with dementia," said Maria Corrada, a UC Irvine epidemiologist and study corresponding author.
The study also found that likelihood of having dementia doubled every five years in women after reaching 90, but not in men. Moreover, women with a higher education appeared to be as much as 45 percent less likely to have dementia compared to women with less education.
The incidence of dementia increases from 65 to 85 years in both men and women. The frequency of dementia increases with age from less than 2 percent for the 65-69-year-olds, to 5 percent for the 75-79-year-olds and to more than 20 percent for the 85-89-year-olds.
"Our findings provide valuable information toward further inquiries into dementia, such as if oldest-old men can live as long with dementia as oldest-old women do, or whether in this age group women develop dementia at a higher rate than men," Corrada added.
The study appears in the July 2 online issue of Neurology, the medical journal of the American Academy of Neurology.