Alzheimer's less likely for men over 90 than women

The chances of having dementia doubled every five years in the 700 women after reaching age 90, but remained largely consistent in the 200 men.

As has been shown in other ages, women with more education were less likely to have dementia than less-educated women.

Previous studies had shown that dementia becomes more and more common starting when people are in their mid-60s through their 80s. For example, fewer than 2 percent of people ages 65 through 69 are estimated to have dementia, compared to 5 percent of those aged 75 to 79 and more than 20 percent of those 85 to 89.

In the new study, 41 percent of both the men and women age 90 and older were found to have dementia.

Dementia involves a loss of brain function, and symptoms of dementia include memory loss, mental disorientation and behavioral changes. It gets worse over time.

(Editing by Maggie Fox and Cynthia Osterman)