Study Suggests Decline in the Incidence of Dementia

The prevalence of dementia is expected to rise as the population ages, but a new study, funded by the National Institutes of Health, suggests that the incidence of dementia is declining in high-income countries. 

The research, published in the New England Journal of Medicine (2016;374(6):523-532), is based on temporal trends in the incidence of dementia over three decades among participants in the Framingham Heart Study (FHS), known to be a reliable source of data. The FHS includes 5205 persons aged 60 years or older who have been under surveillance for incident dementia since 1975. Researchers determined the 5-year incidence of dementia during each of four time periods using Cox proportional hazards models adjusted for age and sex. They also sought to determine the reason for the decreasing risk of dementia by considering risk factors such as education, smoking, blood pressure, diabetes, hypertension, and high cholesterol.

The 5-year age- and sex-adjusted cumulative hazard rates for dementia were 3.6 per 100 persons during the first time period (late 1970s and early 1980s); 2.8 per 100 persons during the second time period (late 1980s and early 1990s); 2.2 per 100 persons during the third time period (late 1990s and early 2000s); and 2.0 per 100 persons during the fourth time period (late 2000s and early 2010s). The incidence declined by 22%, 38%, and 44% during the second, third, and fourth time periods, respectively, relative to the first. However, the factors contributing to this decline in the incidence of dementia among participants in the FHS have not been completely identified. 

FHS senior investigator Sudha Seshadri, MD, professor of neurology at Boston University School of Medicine (Boston, MA) said, “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 or secondary prevention. Effective prevention could diminish in some measure the projected explosion in the number of persons affected with the disease in the next few decades.” The authors caution that this does not mean that the total number of persons with dementia will decrease anytime soon; the burden of dementia is expected to continue to grow as baby boomers age and life expectancy increases.—Amanda Del Signore