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Study examines factors behind decline in dementia incidence

In the United States, as many as 5.2 million people age 65 and older are estimated to have Alzheimer’s disease, the most common form of dementia, and these numbers are expected to rise with an aging population. However, a new NIH-funded study showed a progressive, decades-long decline in dementia incidence (newly reported cases) among older people in Framingham, Mass., and examined factors that may influence this trend.

The report appeared online February 10, 2016, in The New England Journal of Medicine. It was conducted by researchers at Boston University School of Medicine and colleagues.

Researchers following thousands of older volunteers participating in the NIH-funded Framingham Heart Study reported a steady decline in new cases of Alzheimer’s and related dementias over several decades. They tracked the cognitive status of 5,205 volunteers age 60 and older at 5-year intervals during four periods in the 1970s, 1980s, 1990s and 2000s. They also examined how age, education, and vascular risk factors such as blood pressure might influence dementia rates.

Their findings suggest that while the number of people with dementia may be rising due to the aging population, the risk of dementia may have been decreasing in high-income communities such as Framingham. They found:

  • There was a progressive decline in dementia incidence, at any given age, with an average reduction of 20 percent per decade since the 1970s.
  • The amount of education appeared to play a significant role in dementia risk. Among volunteers with at least a high school diploma, dementia incidence declined by 22 percent by the 1980s, 38 percent the 1990s, and 44 percent by the 2000s when compared to the first decade. They also noted that more study participants graduated from high school as the study progressed.
  • A parallel trend in improved cardiovascular health (with the exception of obesity and diabetes) over the decades may have influenced the decline in dementia prevalence. Again, this cardiovascular health improvement was seen only among volunteers who had graduated from high school.
  • The average age at which dementia was diagnosed rose from age 80 in the 1970s to age 85 in the 2000s.

The researchers note that these findings suggest that higher education levels, along with treatment of vascular disease, may have helped delay the onset of dementia. They emphasized that these factors, however, did not explain all of the observed decline, and that more research is needed to fully understand the factors underlying lower incidence of dementia.

The study was supported by the National Heart, Lung, and Blood Institute and the National Institute on Aging, both components of the NIH.

Reference: Satizabel CL, et al. Incidence of dementia over three decades in the Framingham Heart Study. New England Journal of Medicine. Published online Feb. 10, 2016.