Alzheimer's less likely for men over 90 than women

In a study involving 911 people age 90 and older, 28 percent of the men and 45 percent of the women had some type of dementia. Alzheimer's disease is the most common form of dementia in the elderly, and vascular dementia - loss of brain function thanks to a series of small strokes - is second.

While dementia rates remained stable for men through their 90s, they climbed in women, to 27 percent of the women aged 90 to 91 and 71 percent of women aged 98 to 99.

"This difference in prevalence - basically how many people have the disease at any given time - may be because women may live longer once they get diagnosed with dementia than men," said Maria Corrada of the University of California at Irvine, who led the study, said in a telephone interview.

Another possibility noted by the researchers was that relatively few men live to age 90 and beyond, and those who do may be hardy "survivors" with fewer risk factors for dementia.

Experts predict a worldwide surge in dementia cases in the coming decades as populations in many countries age.

"With this (age 90 and beyond) being the fastest-growing segment of the population in the United States and in many other countries too, we have to be prepared for the increasing number of people with this disorder that is very expensive to care for," Corrada said.

But much of the research on old-age dementia has not focused on nonagenarians and older. About three-quarters of people age 90 and up are women.

"Until this study, and a few others, there was very little data on what happens with rates of dementia in extreme old age, once you get beyond 85, up into the 90s and even higher," added Dr. David Hogan of the University of Calgary, who wrote an editorial in the journal Neurology accompanying the study.

Corrada's team studied a population of people 90 and above, most living in southern California. About 10 percent were at least 100.