U.S. dementia rates dropping even as population gets older

Despite fears that dementia rates were going to explode as the population grows older and fatter, and has more diabetes and high blood pressure, a large nationally representative survey has found the reverse. Dementia is actually on the wane. And when people do get dementia, they get it at older and older ages.

Previous studies found the same trend but involved much smaller and less diverse populations, like the mostly white population of Framingham, Mass.

The new study found that the dementia rate in Americans 65 and older fell by 24 percent over 12 years, to 8.8 percent in 2012 from 11.6 percent in 2000. That trend is “statistically significant and impressive,” said Samuel Preston, a demographer at the University of Pennsylvania.

In 2000, people received a diagnosis of dementia at an average age of 80.7; in 2012, the average age was 82.4.

“The dementia rate is not immutable,” said Dr. Richard Hodes, director of the National Institute on Aging. “It can change.”

And that “is very good news,” said John Haaga, director of the institute’s division of behavioral and social research. It means, he said, that “roughly a million and a half people aged 65 and older who do not have dementia now would have had it if the rate in 2000 had been in place.”

The study, published online Monday by the journal JAMA Internal Medicine, included 21,000 Americans 65 and older across all races, education and income levels.

To assess dementia, participants were asked, among other things, to recall 10 nouns immediately and after a delay, to serially subtract seven from 100, and to count backward from 20.

Even with the lower prevalence of dementia, there will be many more older people in the United States over the next few decades, especially people age 85 and older who are at the highest risk. For that reason, the total number of people with dementia should rise, although not as much as had been estimated.