Key points Question What was the prevalence of dementia and mild cognitive impairment (MCI) in the US in 2016? Findings This nationally representative cross-sectional study found that approximately one-third of 3,496 people aged 65 years or older had dementia or MCI. Prevalence rates were similar by sex, but varied by age, education, race, and ethnicity. Meaning The results suggest that there may be disparities in dementia and mild cognitive impairment between older black and Hispanic adults and people with lower educational attainment. |
Summary
Importance
Nationally representative data are critical to understanding the causes, costs, and outcomes associated with dementia and mild cognitive impairment (MCI) in the US and can inform policies aimed at reducing the impact of these conditions in patients, families and public programs. The nationally representative Health and Retirement Study (HRS) is an essential resource for such data, but the HRS substudy that provides dementia diagnostic information was presented more than 20 years ago and more recent data are needed.
Aim
The Harmonized Cognitive Assessment Protocol (HCAP) was developed to update national estimates of the prevalence of MCI and dementia in the US and examine differences by age, race, ethnicity, and sex.
Design, environment and participants
HRS is an ongoing nationally representative longitudinal study of individuals aged 51 years and older with entry dates staggered from 1992 to 2022 and follow-up ranging from 4 to 30 years. HCAP is a cross-sectional random sample of people in HRS who were 65 years or older in 2016.
Of 9972 age-eligible HRS participants, 4425 were randomly selected for HCAP, and 3496 completed a comprehensive neuropsychological test battery and an informant interview, none of whom were excluded. Dementia and MCI were classified using an algorithm based on standard diagnostic criteria and comparing test performance to a robust normative sample.
Main results and measures
National prevalence estimates using population weights.
Results
The mean (SD) age of the study population sample (N = 3496) was 76.4 (7.6) years and 2095 participants (60%) were female. There were 551 participants who identified as Black and non-Hispanic (16%), 382 who identified as Hispanic regardless of race (16%), 2,483 who identified as White and non-Hispanic (71%), and 80 who identified as themselves as another race (2%), including American Indian or Alaska Native, Asian, Native Hawaiian or Pacific Islander, or other self-described race.
A total of 393 individuals (10%; 95% CI, 9-11) were classified as having dementia and 804 (22%; 95% CI, 20-24) as having MCI. Each 5-year increase in age was associated with an increased risk of dementia (weighted odds ratio [OR], 1.95 per 5-year age difference; 95% CI, 1.77-2.14) and MCI (OR, 1.17 per 5 years of age difference, 95% CI, 1.09-1.26).
Each additional year of education was associated with a decreased risk of dementia (OR, 0.93 per year of school, 95% CI, 0.89-0.97) and MCI (OR, 0.94, 95% CI, 0.91-0.97). Dementia was more common among non-Hispanic blacks (OR, 1.81; 95% CI, 1.20-2.75) and MCI in Hispanics (OR, 1.42; 95% CI, 1 .03-1.96) compared to non-Hispanic white people.
Further group comparisons by race and ethnicity were not possible due to small numbers. No differences in prevalence were found between female and male individuals.
Conclusions and relevance
Using a comprehensive neuropsychological test battery and a large sample, the 2016 national prevalence of dementia and MCI found in this cross-sectional study was similar to other US studies, indicating a disproportionate burden of dementia and MCI among old people. Black and Hispanic adults and those with lower education.
Comments
In the first nationally representative study of the prevalence of cognitive decline in more than 20 years, researchers at Columbia University found that nearly 10% of American adults over age 65 have dementia, while another 22% have a mild cognitive impairment .
People with dementia and mild cognitive impairment are more likely to be older, have lower levels of education, and be racialized as black or Hispanic. Men and women have similar rates of dementia and mild cognitive impairment.
Although dementia and mild cognitive impairment are known to be common in the United States, accurate and up-to-date measures of their national prevalence have been scarce.
“Such data are critical to understanding the causes, costs, and consequences of dementia and mild cognitive impairment in the United States, and to inform policies aimed at reducing their impact on patients, families, and public programs,” says Jennifer J. Manly, PhD, senior author of the study and professor of neuropsychology in neurology at the Gertrude H. Sergievsky Center and the Taub Institute for Research on Alzheimer’s Disease and the Aging Brain at Columbia University.
35% dementia rate among 90-year-olds
The study was based on data from 3,500 people enrolled in the nationally representative Health and Retirement Study. Between 2016 and 2017, each participant completed a comprehensive set of neuropsychological tests and in-depth interviews, which were used to develop an algorithm to diagnose dementia or mild cognitive impairment.
Dementia and mild cognitive impairment
Dementia is characterized by cognitive difficulties that begin in adulthood and affect a person’s ability to independently perform everyday activities. Mild cognitive impairment is a classification assigned to people who are believed to be transitioning between normal aging and dementia, but not all people who have mild cognitive impairment will develop dementia.
Rates of dementia and mild cognitive impairment increased sharply with age: 3% of people aged 65 to 69 had dementia, rising to 35% for people aged 90 and older.
“With increasing longevity and aging of the Baby Boom generation, cognitive decline is expected to increase significantly in the coming decades, impacting individuals, families, and programs that provide care and services to people with disabilities.” dementia,” says Manly.
The economic impact of dementia, including unpaid family caregiving, is estimated at $257 billion per year in the United States and $800 billion worldwide.
Disparities in cognitive decline are driven by exposure to structural and social inequalities.
Unlike previous large studies of dementia in the United States, participants in the new study are representative of older adults, allowing researchers to examine differences in the national prevalence of dementia and mild cognitive impairment by age. , race and ethnicity, gender and education.
Data show a disproportionate burden of dementia among older adults who self-identify as black or African American, of mild cognitive impairment among older adults who identify as Hispanic, and both categories of cognitive impairment among people who have fewer opportunities to get education.
“Dementia research in general has largely focused on college-educated people who are racialized as white,” Manly says. “This study is representative of the older adult population and includes groups that have historically been excluded from dementia research but are at increased risk of developing cognitive decline due to structural racism and income inequality. “If we are interested in increasing equity in brain health in later life, we need to know where we stand now and where to direct our resources.”
