Incidence and prevalence of dementia among US Medicare beneficiaries, 2015-21: population based study.

OBJECTIVE: To determine the incidence and prevalence of dementia in a nationally representative cohort of US Medicare beneficiaries, stratified by important subgroups. DESIGN: Population based study. SETTING: Nationwide study between 2015 and 2021. PARTICIPANTS: Fee-for-service Medicare beneficiaries aged 66 or older with at least one year of continuous enrollment. MAIN OUTCOME MEASURES: Incidence and prevalence of dementia, calculated as percentage per person years or percentage of beneficiaries respectively. These metrics were also calculated in key subgroups defined by age, sex, race/ethnicity, and neighborhood socioeconomic status. RESULTS: A total of 5 025 039 incident cases of dementia were documented from 2015 to 2021. The overall age and sex standardized incidence decreased between 2015 and 2021 from 3.5% to 2.8%. Prevalence increased during this time from 10.5% to 11.8%. Male beneficiaries had a higher age standardized incidence than did female beneficiaries in 2015 (3.5% v 3.4%), a difference that widened by 2021 (2.9% v 2.6%; estimated difference-in-difference 0.94, 95% confidence interval (CI) 0.94 to 0.95; P<0.001). 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%); the difference between white and black beneficiaries narrowed from 2015 to 2021 (difference-in-difference 0.92, 95% CI 0.91 to 0.93; P<0.001) as did the difference between white and Hispanic beneficiaries (difference-in-difference 0.88, 0.87 to 0.89; P<0.001). CONCLUSIONS: The incidence of dementia decreased from 2015 to 2021, but the prevalence increased. Disparities in these measures by race/ethnicity, sex, and neighborhood socioeconomic status should motivate future measures to promote health equity.

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