The prevalence of dementia among American seniors of all races has declined in recent years, according to research published on Monday.

The study, conducted by investigators at the University of Michigan, looked into dementia rates across of group of more than 21,000 adults over age 65 between 2000 and 2012. Despite the growing number of adults entering their senior years in that timeframe, dementia prevalence dropped “significantly,” from 11.6% to 8.8%, researchers said.

They noted that the decline could be linked to an increase in seniors’ years of education. The cohort’s average years of education increasing from 11.8 years to 12.7 years over the course of the study.

The research team noted “the full set of social, behavioral and medical factors contributing to the decline in dementia prevalence is still uncertain,” but that their findings back up smaller, previous studies.

Results were published online in JAMA Internal Medicine.