Despite aging population and increases in risk, study finds U.S. decline
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 increasingly older ages.
Previous studies found the same trend but involved much smaller and less diverse populations like the mostly white population of Framingham, Mass., and residents of a fewer areas in England and Wales.
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 who was not associated with the study.
In 2000, people received a diagnosis of dementia at an average age of 80.7；in 2012, the average 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.”
Keith Fargo, director of scientific programs and outreach at the Alzheimer's Association, said the group had been encouraged by some of the previous research showing a decline but had also been “a little bit nervous” about drawing conclusions because the populations in the earlier studies were so homogeneous.
Now, he said of the data, “here is a nationally representative study. It's wonderful news.”
An estimated four million to five million Americans develop dementia each year. It remains the most expensive disease in America - a study funded by the National Institute on Aging estimated that in 2010 it cost up to $215 billion a year to care for dementia patients, surpassing heart disease ($102 billion) and cancer ($77 billion).
The study, published online Monday by the journal JAMA International Medicine, included 21,000 Americans 65 and older across all races, education and income levels, who participate in the Health and Retirement Study, which regularly surveys people and follows them as they age. The National Institute on Aging funded the work but was not involved with the data collection, analysis or interpretation.
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. The test was based on extensive research indicating it was a good measure of memory and thinking skills.
Participants also were
asked about their education levels, income and health.
In a way, the dementia decline might seem unexpected. It occurred despite an increase in diabetes - the diabetes prevalence among older Americans surged to 21 percent in 2012 from 9 percent in 1990, though it began to fall very recently. And, the study found, diabetes increased the risk of dementia by 39 percent.
