A new study found that the rate of dementia among U.S. adults aged 65 and older dropped 30.1% from 2000 to 2016.

The study by the nonprofit research organization RAND used data from over 21,000 participants over the span of 16 years. The findings were published Monday in the Proceedings of the National Academy of Sciences.

Authors cite rising levels of education, smoking reduction, and improved treatment for heart risk factors as possible factors behind the decline.

In 2000, 22% of men and 12% of women in the study were college-educated. In 2016, education rate rose to 34% and 23% respectively while dementia rates dropped, showing that education may be one of the more important driving factors in the disease's prevalence.

"Closing the education gap across racial and ethnic groups may be a powerful tool to reduce health inequalities in general and dementia inequalities in particular, an important public health policy goal," said lead author Peter Hudomiet in a RAND press release.

"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," Hudomiet said.

The age-adjusted prevalence of dementia in 2000 was 12.2%. In 2016, that number was cut by nearly one-third to 8.5%. Researchers measured differences in dementia prevalence by age, sex, ethnicity, education, and lifetime earnings. Data showed narrowing inequalities among all metrics.

Dementia prevalence dropped by 7.3 percentage points among Black men and 3.9 percentage points among women over the span of the study. Comparatively, dementia prevalence among white men dropped 2.7 percentage points.

"Despite these favorable trends, we still find substantial dementia inequalities across subpopulations; women, racial and ethnic minority groups, and those with lower education face substantially higher chances of living with dementia," authors said of the findings.

Over six million adults aged 65 and older suffered from dementia in 2021. Although rates have declined and disparities have narrowed, researchers expect a rise in dementia prevalence in the future as more of the population ages.

"Because age is the strongest risk factor for dementia, it has been predicted that increasing life expectancies will substantially increase the prevalence of Alzheimer's disease and related dementias from about 50 to 150 million worldwide by 2050," authors of the study said.