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One-third of older Americans have dementia

As people live for longer, the prevalence of dementia increases. This trend is apparent in all countries in the world where medical and health interventions are able to extend lifespan. Currently, around 55 million people suffer from dementia and there are some 10 million new cases diagnosed each year. This number is expected to rise to 78 million sufferers in 2030 and more than 100 million by 2050. 

Dementia is the seventh leading cause of death among all diseases and one of the major causes of disability and dependency among older people worldwide. It is characterized by cognitive difficulties that begin in adulthood and affect a person’s ability to function independently and perform everyday activities. Mild cognitive impairment (MCI), on the other hand, is thought to indicate a transitioning phase between normal aging and dementia, although not everyone who has MCI will go on to develop dementia.

Since these conditions have significant physical, psychological, social and economic impacts, not only for sufferers themselves, but also for their carers, families and society at large, it is critical that authorities have an up-to-date understanding of their prevalence in populations, in order to formulate appropriate support policies. 

In the first nationally representative study of cognitive impairment prevalence in more than 20 years, Columbia University researchers, along with colleagues from several other U.S. universities, have analyzed data from individuals enrolled in the nationally representative Health and Retirement Study. This is an ongoing study that started in 1992 and the current researchers randomly selected a subsample of 3,500 participants who were 65 years or older in 2016. 

Known as the Harmonized Cognitive Assessment Protocol (HCAP), the current study was developed to update national estimates of the prevalence of MCI and dementia in the U.S. and to examine differences by age, race, ethnicity, and gender. Participants completed a comprehensive set of neuropsychological tests and in-depth interviews, and dementia and MCI were classified using an algorithm based on standard diagnostic criteria and comparing test performance to a robust normative sample.

“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.

Although dementia and MCI are known to be common in the U.S., accurate, up-to-date measures of their national prevalence have been infrequent. In addition, previous estimates of dementia and MCI have tended to focus on populations that are college-educated and White, and have not been nationally representative. Participants in the new study are representative of older adults and this allows researchers to examine differences in the national prevalence of dementia and MCI by age, race and ethnicity, gender, and education level. 

The results of the analysis, published in the JAMA Neurology, show that the incidence of dementia and MCI rises sharply with age: 3 percent of people between 65 and 69 had dementia, while the prevalence was 35 percent among people who were aged 90 and over.  Overall, the study found that almost 10 percent of U.S. adults aged 65 and older have dementia, while another 22 percent have mild cognitive impairment. 

In addition to the association with age, 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 of both categories of cognitive impairment among people who had fewer opportunities to obtain higher education.

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. And this is set to increase in future as populations age and people experience greater longevity.

“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.

“Dementia research in general has largely focused on college-educated people who are racialized as white,” she explains. “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.”

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By Alison Bosman, Staff Writer

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