Dementia rates fall, but aging American may halt trend

CHICAGO -- New research documents a decline in dementia rates, but experts said the rising numbers of older Americans may halt that trend unless better ways are found to keep brains healthy.

The study released Monday shows the rate of Alzheimer's disease and other dementias in adults aged 65 and up dropped to about 9 percent in 2012 from nearly 12 percent in 2000, continuing a decline noted in earlier research.

Older adults with the most schooling had the lowest dementia rates, and the average education level increased during the study years.

Alzheimer's is the most common form of dementia, which also can be caused by strokes, Parkinson's disease and other conditions.

Led by University of Michigan researchers, the study was published in JAMA Internal Medicine. The National Institute on Aging paid for the research.

Researchers analyzed nationally representative government surveys of about 10,500 older adults in both years, including some living in nursing homes. They were interviewed and given mental tests by phone or in person; spouses or relatives responded for those impaired by dementia or other illness.

The dementia rate declined amid a rise in diabetes and heart disease. Both increase risks for Alzheimer's and other dementias, but the researchers say better treatment for both diseases may explain the results.

Obesity rates also increased, and dementia was most common among underweight adults. Previous research has shown weight loss may precede dementia by several years, and late-life obesity may be healthier than being underweight. But a journal editorial said more research is needed to determine whether excess pounds in older age somehow protect the brain.

Dementia was most common in the oldest adults; in 2012, almost 30 percent of adults age 85 and up were afflicted versus just 3 percent of those ages 65 to 74.

The number of adults age 85 and older is rising rapidly and expected to triple by mid-century.

John Haaga, director of the National Institute on Aging's behavior and social research division, said dementia rates would have to decline much more sharply than they have to counteract that trend.