New US dementia cases in decline, but continued rise in people living with the condition, finds study

New cases of dementia in the United States declined from 2015 to 2021, but the number of people living with the condition continued to rise due to population aging, with nearly 2.9 million traditional Medicare beneficiaries (around 12%) living with a dementia diagnosis in 2021, finds a study published by The BMJ.

What’s more, a greater burden of dementia was seen in marginalized and low-resource communities, highlighting the importance of policy approaches to promote equitable dementia care, say the researchers.

It’s estimated that dementia will more than double to affect nearly 14 million people in the US by 2060, with far-reaching social and economic implications. But high-quality evidence on recent trends in new cases (incidence) and prevalence (existing cases) of dementia in routine clinical practice is scarce.

To address this, researchers used medical claims data to determine the incidence and prevalence of dementia by race, sex, and neighborhood deprivation in more than 5 million fee-for-service Medicare beneficiaries aged 66 or older between 2015 and 2021.

After accounting for differences in age and sex, the overall incidence of dementia decreased between 2015 and 2021 from 3.5% to 2.8% but prevalence increased during this time from 10.5% to 11.8%.

Male beneficiaries had a higher incidence than did female beneficiaries of the same age in 2015 (3.5% v 3.4%), a difference that widened by 2021 (2.9% v 2.6%).

To add context to these figures, the authors note that while men have a higher incidence than women of the same age, the majority of people with dementia are female (60% in 2021), so the population-level impact of dementia is most prominent among women (likely because more women live long enough to develop dementia).

Furthermore, the burden of dementia was unequally distributed, with the highest incidence and prevalence of dementia among Black beneficiaries and those living in socioeconomically deprived neighborhoods.

For example, incidence was highest in 2015 for Black beneficiaries (4.2%), followed by Hispanic beneficiaries (3.7%) and white beneficiaries (3.4%), and in 2021 for Black beneficiaries (3.1%), followed by white beneficiaries (2.8%) and Hispanic beneficiaries (2.6%).

Possible reasons behind the reduced incidence of dementia include better management of cardiovascular risk factors and COVID-19 deaths among patients who would otherwise have been diagnosed with dementia, while the rise in prevalence is likely due to more people surviving long enough to develop dementia, or more people living longer after being diagnosed with dementia, say the authors.

This is an observational study so no firm conclusions can be drawn about cause and effect, and the authors acknowledge several limitations, including that Medicare claims data may not be completely accurate, are limited in their classification of race and ethnicity, and may not apply to patients with different insurance cover.

Nevertheless, they say their results are based on a large national sample of routinely collected data, which allowed them to accurately reflect diagnostic patterns seen in general clinical practice and fill an important gap in the literature.

They call for further studies to probe the mechanisms behind the observed differences and say disparities in these measures by race / ethnicity, sex, and neighborhood socioeconomic status should motivate future measures to promote health equity.

These results are consistent with findings from other studies, but using routine data to uncover underlying trends presents challenges, say UK researchers in a linked editorial.

For example, they point out that as the marginalized minorities are under-represented in Medicare fee-for-service plans, true inequalities by area deprivation index are likely to be larger than those reported. 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.

As such, they say these findings “highlight not just the need for improvement in services for people living with dementia in communities where higher incidence and prevalence might be expected, but also the need to implement policies for improvement in risk factor profiles across populations from early life onward.”