Prevalence of Dementia in the US Continues to Decline

A study of older Americans has found that the prevalence of dementia has decreased significantly, from 11.6% in 2000 to 8.8% in 2012. It cited increased average educational attainment and improved diabetes treatments as factors that could explain the drop in dementia rates.

The study, which was published in JAMA Internal Medicine, used data from the 2000 and 2012 waves of the Health and Retirement Study (HRS) survey of US adults 65 or older. The surveys asked the 21,057 participants about their demographic characteristics and health measures and assessed their cognitive function with a range of short tests. Respondents unable or unwilling to participate in the survey could be represented by a proxy respondent.

The proportion of surveyed individuals with dementia decreased significantly, from 11.6% in 2000 to 8.8% in 2012. The researchers age- and sex-standardized the 2012 cohort to the 2000 cohort, resulting in a dementia prevalence of 8.6% in 2012 due to the increased proportion of respondents 85 years or older. The percentage of respondents categorized by the assessment as having cognitive impairment but no dementia also decreased, falling from 21.2% to 18.8% over the 12-year time frame.

The 2012 cohort, along with having a larger proportion of respondents 85 years or older, had on average almost 1 more year of education compared to the 2000 cohort. In 2000, 32.6% of respondents had fewer than 12 years of education, but by 2012 that proportion had dropped to 20.6%. The study authors wrote that this increase in educational attainment could explain some of the decline in dementia prevalence, citing studies on the “cognitive reserve” built by education that can help protect individuals from the effects of dementia.

Along with more years of education and higher net worth, being overweight or obese was associated with lower odds of dementia. Older age, having a history of stroke or diabetes, being African American or Hispanic, and being underweight were each associated with increased odds of dementia.

Diabetes, which was associated with 39% higher odds of dementia, increased in prevalence from 2000 to 2012. According to the study authors, the decreased dementia risk in spite of increased diabetes prevalence could be attributed to improvements in diabetes treatments during this time period. Still, they caution, the complete combination of social, behavioral, and medical factors contributing to the decreased prevalence of dementia is still uncertain.

“Continued monitoring of trends in dementia incidence and prevalence will be important for better gauging the full future societal impact of dementia as the number of older adults increases in the decades ahead, as well as for clarifying potential protective and risk factors for cognitive decline,” they wrote.

The authors stated that the findings from this study are similar to others that have indicated a decline in dementia prevalence over time in the US and other high-income countries.

“This is good news,” said lead author Kenneth M. Langa, MD, PhD, in a video interview accompanying the JAMA article. “This is in line with a prior study that we did with HRS looking at an earlier time period from 1990 through 2000, so we think, again, this is optimistic trends over the last 25 years or so in the United States with improving brain health.”