More Americans Have Dementia, Despite Fewer New Cases

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Those living in socioeconomically deprived neighborhoods had highest incidence and prevalence

by
Judy George, Deputy Managing Editor, MedPage Today
May 20, 2025 • 3 min read

Dementia incidence decreased in the U.S. from 2015 to 2021 but prevalence increased, a study of Medicare fee-for-service beneficiaries showed.

Age- and sex-standardized incidence rates fell from 3.5% in 2015 to 2.8% in 2021, but prevalence rose from 10.5% to 11.8%, reported Jay Lusk, MD, of Duke University School of Medicine in Durham, North Carolina, and colleagues.

Approximately 5 million cases of incident dementia were documented from 2015 to 2021, Lusk and co-authors noted in The BMJ.

In 2015, men had a higher age-standardized incidence compared with women (3.5% vs 3.4%), and the difference widened by 2021 (2.9% vs 2.6%; estimated difference-in-difference 0.94, 95% CI 0.94-0.95, P<0.001). While men had higher incidence than women of the same age, women had higher prevalence (60.2% in 2021).

Incidence was highest in 2015 for Black beneficiaries (4.2%), followed by Hispanic beneficiaries (3.7%) and white beneficiaries (3.4%). In 2021, incidence was still highest for Black beneficiaries (3.1%), but for white beneficiaries, it was 2.8% and for Hispanic beneficiaries, it was 2.6%.

The difference between white and Black beneficiaries narrowed from 2015 to 2021 (difference-in-difference 0.92, 95% CI 0.91-0.93, P<0.001) as did the difference between white and Hispanic beneficiaries (difference-in-difference 0.88, 95% CI 0.87-0.89, P<0.001).

Those living in socioeconomically deprived neighborhoods had the highest incidence and prevalence, Lusk and colleagues noted.

“Although the overall incidence of dementia decreased over the study period, prevalence increased substantially, and our results indicate that nearly 2.9 million fee-for-service Medicare beneficiaries and nearly 4.5 million Medicare beneficiaries (including projections to the Medicare Advantage population) were likely living with a diagnosis of dementia in 2021,” they wrote.

Marginalized minorities are under-represented in Medicare fee-for-service numbers, and “true inequalities by area deprivation index are likely to be larger than those reported,” observed Sara Ahmadi-Abhari, MD, PhD, of Imperial College London, and Carol Brayne, MD, of the University of Cambridge in England, in an accompanying editorial.

“Better health monitoring, greater awareness, and diagnosis at an earlier stage could also drive numbers up for the more advantaged groups, further masking socioeconomic inequalities,” they noted.

“The geographical variation in estimates of incidence/prevalence is likewise compounded by factors such as regional clustering of the under-represented groups and differences in access, quality of care, and attitudes towards diagnosis and treatment,” they added. “Without accounting for these factors, estimates derived from routine data and insurance claims cannot be taken at face value. Even then, uncovering the true underlying trends is not easy.”

Moreover, people with dementia rarely have dementia alone, Lusk stated in an opinion article. “The presence of other severe chronic conditions, such as cardiovascular disease and diabetes mellitus, is high compared to adults without dementia,” he pointed out.

“Our study estimates that more than 40% of people with dementia have cerebrovascular disease, 30% have depression, and more than 80% have hypertension,” Lusk wrote. “These comorbid conditions each carry their own additive or multiplicative effects that reduce quality of life.”

Lusk and colleagues used Medicare fee-for-service claims data to determine the incidence and prevalence of dementia by race, sex, and neighborhood deprivation in 5,025,039 incident cases documented from 2015 to 2021. Beneficiaries were ages 66 and older, and those enrolled in Medicare Advantage plans were not included.

Dementia incidence may have been influenced by better management of cardiovascular risk factors, or by deaths due to COVID-19 in people who might otherwise have been diagnosed with dementia, the researchers suggested. The rise in prevalence was likely due to people surviving long enough to develop dementia or living longer after a dementia diagnosis, they added.

The findings suggest a higher prevalence of dementia than estimates from previous global studies, “which may be attributable to greater capture of beneficiaries owing to our use of routinely collected data, misclassification due to our reliance on billing data, or differences between risk factors and diagnostic patterns in the U.S. compared with other countries,” Lusk and colleagues noted.