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, Massachusetts, and residents of a few 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 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.”
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 new data, “here is a nationally representative study. It’s wonderful news.”
An estimated 4 million to 5 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 Internal 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. It began to fall only very recently. And, the study found, diabetes increased the risk of dementia by 39 percent.
More older people today also have cardiovascular risk factors – high levels of blood pressure, blood sugar and cholesterol – which increase the risk of dementia. But more are taking medications for those conditions, so perhaps better control of those risk factors played a role in the decline.
The findings about obesity were especially puzzling. Compared with people of normal weight, overweight people and obese people had a 30 percent lower risk of dementia, the study found. Underweight people had a risk 2.5 times as great. Yet the obesity picture is muddled because other studies have found that obesity in middle age increases dementia risk in old age.
Dementia rate declines
New research documents another decline in dementia rates but experts say 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 can also 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, while dementia was most common among underweight adults. Previous research has shown weight loss may precede dementia by several years and that late-life obesity may be healthier than being underweight. But a journal editorial says 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 aged 85 and up were afflicted versus just 3 percent of those 65-74.
The number of adults aged 85 and older is rapidly rising 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.
The Alzheimer’s Association estimates that about 5 million people aged 65 and older have Alzheimer’s, and that is expected to rise to almost 14 million by 2050.
The average education level climbed during the study. About 45 percent of older adults had at least 13 years of education in 2012, versus about 33 percent in 2000.
Previous studies have found less dementia in highly educated people, but it isn’t known whether education somehow protects the brain from dementia or if it helps people compensate for brain changes linked with Alzheimer’s or other dementias.
Studies on brain-training exercises have had conflicting results.
Haaga said more research is needed to explain the education-dementia link and to explore potential treatments that mimic the effects of education to stave off dementia.
Meantime, experts say there are ways to help keep your brain healthy. That includes avoiding smoking, eating healthy foods and getting plenty of exercise. Experts also advise staying mentally active — take a class, learn a new skill or hobby.
“There is reason to hope that you’re not doomed if you didn’t get massive education early in life,” Haaga said.