A study published Monday in JAMA Neuroscience In 2016, more than one-third of Americans age 65 and older were diagnosed with dementia or mild cognitive impairment—but the prevalence of the conditions varied by age, education, and race and ethnicity.
Study details and key findings
For the study, researchers collected data from 3,496 participants in the Harmonized Cognitive Assessment Protocol (HCAP) project, part of the ongoing, longitudinal Health and Retirement Study (HRS). The HCAP included a cross-sectional random sample of HRS participants aged 65 and older in 2016.
Between June 2016 and October 2017, HCAP participants were required to complete a comprehensive neuropsychological examination and personal interview.
On average, participants were 76.4 years old. Overall, 60% were female, 71% were white, 16% were black, 11% were Hispanic, and 2% identified as another race.
Dementia and mild cognitive impairment were classified by an algorithm based on standard diagnostic criteria. The researchers then compared the participants’ test performance to a standardized sample. To estimate the prevalence of dementia and mild cognitive impairment in the United States, researchers used population weights.
According to study author Jennifer Manley Columbia University Irving Medical Centerand colleagues, 10% of participants had dementia in 2016 and 22% had mild cognitive impairment.
Although the prevalence of dementia is similar in men and women, it varies by age, education, and race and ethnicity.
For example, compared with white participants, dementia was more common among black participants and mild cognitive impairment was more common among Hispanic participants.
With every five-year increase in age, participants experienced an increased risk of dementia and mild cognitive impairment. For example, 35% of people aged 90 and over had dementia – a significant jump from just 3% of participants aged 65-69.
“Each additional year of education was associated with a decrease in the risk of dementia,” the study found.
While the findings mark the first representative study of cognitive impairment conducted in 20 years, the study authors noted that they are similar to other recent estimates of dementia prevalence in the United States.
Because the findings represent a snapshot in time, they cannot accurately assess rates of cognitive impairment or rates of progression for individuals with mild cognitive impairment, the authors said.
In addition, the authors noted that other longitudinal studies have determined that mild cognitive impairment classifications may be inconsistent, with many people falling into the normal cognitive classification at subsequent appointments.
Finally, the cross-sectional design of the HCAP study “does not allow for examination of survivorship bias, which may increase prevalence if some groups live longer with dementia or underestimate estimates in groups with higher mortality,” the authors added.
Still, “[b]”The HCAP study, which is part of the Nationally Representative and Longitudinal Health and Retirement Study, data not only shows the burden of dementia now, but will be used in the future to track trends in the burden of dementia over the next decades,” said co-author Kenneth Longa. University of Michigan.
“With increasing longevity and the aging of the baby boom generation, cognitive impairment is expected to increase substantially over the next few decades, impacting individuals, families and programs that provide care and services to people with dementia,” Manley said.
“Following those trends is important given the potential impact of COVID and other recent population health changes on dementia risk in the coming decades,” Longa added. (George, MedPage Today, 10/24; Mueller, The Hill, 10/24; Manley et al., JAMA Neuroscience10/24 [subscription required])