Dementia is on the decline, according to a new analysis of health records from thousands of people in one Massachusetts town.
The new report, using data from the long-running Framingham Heart Study, shows that dementia rates have decreased by 44 percent since the late 1970s and early 1980s, with nearly all of that drop among high school graduates.
It was a collective reduction in all causes of senility that produced the significant fall, researchers said. Dementia caused by vascular diseases, such as stroke, accounted for the much of the drop. Alzheimer's disease showed a reduction, but it wasn't dramatic, and could be a statistical fluke, they said.
"There was a trend there" for Alzheimer's, said Dean Hartley, director of science initiatives with the Alzheimer's Association. It shows "there may be modifiable lifestyles that may lower your risk for Alzheimer's."
So many people are entering the age when dementia becomes a threat and life expectancy is increasing so rapidly, the decline in rates of dementia will not translate to an overall drop in the number of dementia cases, cautioned senior author Dr. Sudha Seshadri, a professor of neurology at the Boston University School of Medicine.
"We don't know completely what's bringing down the rates," she told Reuters Health. "The good news is, we are doing something right. The bad news is we need to understand this much better if we want to effectively continue the trend."
The Framingham study is based in a predominately-white Massachusetts town west of Boston where thousands of residents have been closely followed by doctors since 1948. The new analysis, reported in the New England Journal of Medicine, looked at dementia rates in four 5-year blocks and used data from 5,205 individuals.
Dementia rates were 3.6 percent among people aged 60 years and older beginning in 1977, falling to 2.8 percent for the block of people who were over 60 beginning in 1986, then 2.2 percent for the block starting in 1992 and 2.0 percent for the most recent block, from 2004 to 2008.
Those declines translate to reductions of 22 percent, 38 percent and 44 percent in the second, third and fourth period, respectively, compared to the rate in the early years.
The researchers said some of the drop may be due to declines in rates of stroke, heart failure and atrial fibrillation, as well as better treatments for those conditions, "but none of these trends completely explain the decrease in the incidence of dementia."
Residents without a high school diploma showed no decline in dementia, perhaps because improvements in heart health were only seen among people who had graduated from high school, the study team notes.
Dr. Paul Schulz, a dementia neurologist at the University of Texas Health Science Center in Houston, who was not connected to the research, pointed out that "there's a lot of healthcare access issues related to education (and graduates) may have better insurance to see their doctor more often," which might have affected the results.
In addition, he said, "People who have more education may be blessed with more brain power. They may have more ability to lose function before they develop symptoms. In this study they're speculating that getting more education might be valuable, but it might be a chicken and egg question here."
Dementia also tended to show up later in life as time went on, the study found. The average age of diagnosis was 80 during the late 1970s and 85 in the most recent group.
"Rising educational levels might have contributed to the 5-year delay we observed in the mean age at onset of clinical dementia," the researchers said.
"One of the limitations of the Framingham Heart Study is that the participants are overwhelmingly of European ancestry; therefore, our findings would need to be replicated in groups that include a larger number of participants of other races and ethnic backgrounds," they cautioned.
Hartley said it's important to fund more research to see what lifestyle changes might lower the risk further. "A number of things people to do to stay healthy" such as exercise, a better diet and social stimulation "could protect their brain," he said