In people ages 65 and up, prevalence of dementia dropped by 3.7 percentage points. Disparities also decreased between white and Black men and between men and women.

"The reasons for the decline in the prevalence of dementia are not certain, but this trend is good news for older Americans and the systems that support them," said lead author Péter Hudomiet, an economist at RAND, a nonprofit research organization.

"This decline may help reduce the expected strain on families, nursing homes and other support systems as the American population ages," Hudomiet added in a RAND news release.

In 2000, the age-adjusted prevalence of dementia was 12.2% for people over 65. By 2016 it was 8.5%, a nearly one-third drop. The rate of decline was especially rapid between 2000 and 2004, the study found.

Gaps in dementia rates between Black and white men narrowed over the years, with prevalence dropping 7.3 percentage points among Black men during those years, compared to dropping 2.7 percentage points among white men.

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