One in ten older Americans has dementia, according to first nationally representative study in more than 20 years

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, Ph.D., 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.

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.

"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."

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.

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."