Summary: A new study reveals that 10% of adults over the age of 65 in the USA have dementia, while another 22% suffer from mild cognitive impairment.
Source: Columbia University
In the first nationally representative study of cognitive impairment prevalence in more than 20 years, Columbia University researchers have found almost 10% of U.S. adults ages 65 and older have dementia, while another 22% have mild cognitive impairment. People with dementia and mild cognitive impairment are more likely to be older, have lower levels of education, and to 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, up-to-date measures of their national prevalence were scarce.
“Such data are critical for understanding the causes, costs, and consequences of dementia and mild cognitive impairment in the United States, and for informing policies aimed at reducing their impact on patients, families, and public programs,” says Jennifer J. Manly, PhD, the study’s lead author 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.
Dementia rate 35% among people in their 90s
The study was based on data on 3,500 individuals 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 for diagnosing 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 thought to be transitioning between normal aging and dementia, but not everyone who has mild cognitive impairment will go on to develop dementia.
Rates of dementia and mild cognitive impairment rose sharply with age: 3% of people between 65 and 69 had dementia, rising to 35% for people age 90 and over.
“With increasing longevity and the aging of the Baby Boom generation, cognitive impairment is projected to increase significantly over the next few decades, affecting individuals, families, and programs that provide care and services for people with dementia,” Manly says.
The economic impact of dementia, including unpaid family caregiving, is estimated to be $257 billion per year in the United States and $800 billion worldwide.
Disparities in cognitive impairment 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, enabling researchers to examine differences in the national prevalence of dementia and mild cognitive impairment by age, race and ethnicity, gender, and education.
The data show a disproportionate burden of dementia among older adults who self-identified 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 had fewer opportunities to obtain education.
Less than high school
College degree or more
“Dementia research in general has largely focused on college-educated people who are racialized as white,” says Manly. “This study is representative of the population of older adults and includes groups that have been historically excluded from dementia research but are at higher risk of developing cognitive impairment because of structural racism and income inequality. If we’re interested in increasing brain health equity in later life, we need to know where we stand now and where to direct our resources.”
The study was published online Oct. 24 in the journal JAMA Neurology.
The study is titled, “Estimating the Prevalence of Dementia and Mild Cognitive Impairment in the US: The 2016 Health and Retirement Study Harmonized Cognitive Assessment Protocol Project.”
The other contributors: Richard N. Jones (Brown University Warren Alpert Medical School), Kenneth M. Langa (University of Michigan), Lindsay H. Ryan (University of Michigan), Deborah A. Levine (University of Michigan and Veterans Affairs Center for Clinical Management Research, Ann Arbor), Ryan McCammon (University of Michigan), Steven G. Heeringa (University of Michigan), and David Weir (University of Michigan).
Estimating the Prevalence of Dementia and Mild Cognitive Impairment in the US: The 2016 Health and Retirement Study Harmonized Cognitive Assessment Protocol Project
Nationally representative data are critical for 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 on patients, families, and public programs. The nationally representative Health and Retirement Study (HRS) is an essential resource for such data, but the HRS substudy providing dementia diagnostic information was fielded more than 20 years ago and more recent data are needed.
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, Setting, and Participants
HRS is an ongoing longitudinal nationally representative study of people 51 years and older with staggered entry dates from 1992 to 2022 and follow-up ranging from 4 to 30 years. HCAP is a cross-sectional random sample of individuals 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 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.
Groups were stratified by age, sex, education, race, and ethnicity.
Main Outcomes and Measures
National prevalence estimates using population weights.
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 self-identified as Black and not Hispanic (16%), 382 who self-identified as Hispanic regardless of race (16%), 2483 who self-identified as White and not Hispanic (71%), and 80 who self-identified as another race (2%), including American Indian or Alaska Native, Asian, Native Hawaiian or Pacific Islander, or another 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.
Every 5-year increase in age was associated with higher 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-year age difference, 95% CI, 1.09-1.26). Each additional year of education was associated with a decrease in 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 Black individuals (OR, 1.81; 95% CI, 1.20-2.75) and MCI in Hispanic individuals (OR, 1.42; 95% CI, 1.03-1.96) compared with non-Hispanic White individuals.
Other group comparisons by race and ethnicity were not possible owing to small numbers. No differences in prevalence were found between female individuals and male individuals.
Conclusions and Relevance
Using a comprehensive neuropsychological test battery and large sample, the national prevalence of dementia and MCI in 2016 found in this cross-sectional study was similar to that of other US-based studies, indicating a disproportionate burden of dementia and MCI among older Black and Hispanic adults and those with lower education.