Many experts predict that as people live longer, the prevalence of dementia will climb. However, a study published February 11 in the New England Journal of Medicine now suggests the incidence of dementia may be falling.
“Currently, there are no effective treatments to prevent or cure dementia,” coauthor Sudha Seshadri, M.D., a professor of neurology at Boston University School of Medicine, said in press statement. “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.”
Currently 47.5 million people worldwide have some form of dementia, according to the World Health Organization. The total number of people with dementia is projected to reach 75.6 million in 2030 and almost triple to 135.5 million by 2050, barring medical advances to prevent or cure the disease.
To assess the progression of dementia in a sample of adults over time, Seshadri and her colleagues analyzed data from 5,205 people aged 60 and older who were participants in the Framingham Heart Study, a community-based, longitudinal cohort study that was initiated in 1948. Since 1975, the cognitive status of the original cohort has been regularly monitored via the Mini-Mental State Examination, neurological and neuropsychological examinations, and subjective memory questioning.
By using statistical models adjusted for age and sex, the researchers determined the incidence of dementia during each of four distinct periods: from the late 1970s to early 1980s (first epoch), from the late 1980s to early 1990s (second epoch), from the late 1990s to the early 2000s (third epoch), and from the late 2000s to the early 2010s (fourth epoch). The researchers also examined the interactions between epoch and age, sex, apolipoprotein E ε4 status, and educational level.
The researchers found a progressive decline in dementia over the 30-year period, with incidence rates, relative to the first epoch, declining by 22 percent, 38 percent, and 44 percent during the second, third, and fourth epochs, respectively. This risk reduction was observed only among persons who had at least a high school diploma.
The participants in the Framingham Heart Study also had improvements in most indicators of cardiovascular health, with the exception of a trend toward increasing prevalence of diabetes and obesity.
“Our study offers cautious hope that some cases of dementia might be preventable or at least delayed,” the researchers concluded. “However, it also emphasizes our incomplete understanding of the observed temporal trend and the need for further exploration of factors that contribute to this decline in order to better understand and possibly accelerate this beneficial trend.”
The study was funded by the National Institutes of Health. ■
An abstract of “Incidence of Dementia Over Three Decades in the Framingham Heart Study” can be accessed
here.
