Women over 90 are significantly more likely to have dementia than men of the same age, according UC Irvine researchers involved with the 90+ Study, one of the nation's largest studies of dementia and other health factors in the fastest-growing age demographic.

The researchers reviewed an analysis of 911 people enrolled in the 90+ Study. Of those, 45 percent of the women had dementia, as opposed to 28 percent of the men. The analysis did not determine when the subjects first experienced dementia.

The 90-plus age group, or the "oldest old," is the fastest growing segment of the population, according to the U.S. Census. While there are currently nearly 2 million nonagenarians in the U.S. alone, that number is projected to increase to 10 to 12 million by the middle of the century, raising concerns that the current health care system may not be able to accommodate this population.

"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 appears in the July 2 online issue of Neurology, the medical journal of the American Academy of Neurology.

Research has shown that dementia prevalence for both men and women increases from age 65 to 85. 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.

The UC Irvine study, conducted in Laguna Woods, Calif., is among the few to look at dementia in people over age 90. It found that the likelihood of having dementia doubled every five years in women after reaching 90, but not in men. The results also showed that women with a higher education appeared to be as much as 45 percent less likely to have dementia compared to women with less education.

With women comprising three-quarters of the 90-plus population, the study raises questions why these women nonagenarians are more likely to have dementia than men.

"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 said.

Dementia, a progressive brain dysfunction, leads to a gradually increasing restriction of daily activities. The most well-known type of dementia is Alzheimer's disease. Symptoms of dementia include memory loss, cognitive disorientation and behavioral changes. Dementia affects not only patients but also those surrounding them, as most patients require long-term care.

About the 90+ Study: Initiated in 2003, the 90+ Study performs clinical, pathological and genetic research in people 90 or older, the fastest-growing segment of the population. With a cohort of 1,100 participants, the 90+ team has assembled one of the largest prospective studies of oldest old subjects in the world. Results obtained thus far have provided researchers across the globe with valuable information about aging. The study, run through the Clinic for Aging Research and Education in Laguna Woods, Calif., is directed by Dr. Claudia Kawas, the Nichols Chair in Clinical Neuroscience.

Study co-authors are Dr. Claudia Kawas and Daniel Berlau from UC Irvine, Ron Brookmeyer from Johns Hopkins University, and Annlia Paganini-Hill of USC. The study was supported by the National Institutes of Health and the Nichols Chair in Clinical Neuroscience.