Despite an aging population, a new study says dementia rates in the United States are dropping, but further research is needed to pinpoint the reason.
Writing in The New England Journal of Medicine, researchers from Boston University say the findings may offer hope that some cases of dementia may be preventable or delayed.
Using data from the Framingham Heart Study, or FHS, researchers found that over the past 40 years, there has been a decrease in the rates of dementia, with declines of 20 percent per decade since the 1970's, when data was first collected. The FHS is a project of the National Heart, Lung, and Blood Institute and Boston University.
FHS participants’ health has been monitored since 1975, using information gleaned from “FHS exams, outside clinical records, interviews with family members, and the examination of participants suspected of having a neurological problem by neurologists and neuropsychologists.”
For dementia caused by strokes and other vascular issues, the decrease was more pronounced, according to researchers. They also found that there was a decrease in dementia caused by heart disease.
This, they said, points to “the importance of effective stroke treatment and prevention of heart disease.”
Another factor appeared to be education levels, with declines in dementia only seen in those with a high school education or more.
"Currently, there are no effective treatments to prevent or cure dementia; however, our study offers hope that some of the dementia cases might be preventable -- or at least delayed -- through primary (keep the disease process from starting) or secondary (keep it from progressing to clinically obvious dementia) prevention," said Sudha Seshadri, a professor of neurology at Boston University School of Medicine and FHS senior investigator. "Effective prevention could diminish in some measure the projected explosion in the number of persons affected with the disease in the next few decades," she said.
Researchers say further study is needed, including with a more diverse group of subjects, as the FHS participants are “overwhelmingly of European ancestry.” The researchers cited the need to look at diet and physical activity.
“It is very likely that primary and secondary prevention and better management of cardiovascular diseases and stroke, and their risk factors, might offer new opportunities to slow down the currently projected burden of dementia for the coming years," said Carole Dufouil, a research director with the French biomedical institution INSERM (French Institute of Health and Medical Research).
Despite the apparent slowdown in rates, the raw number of dementia cases is still expected to rise due to an overall aging population and people living longer. For example, the researchers said that as the population ages, by 2025, there could be 7.1 million people with Alzheimer's and other forms of dementia. That would be a 40 percent increase from the 5.1 million today. By 2050, there could be 13.8 million people with dementia.
Globally, the number of people with dementia is around 47.5 million, according to the World Health Organization. That is expected to rise to 75.6 million in 2030 and 135.5 million by 2050.
Here's a short video about the findings: