Dementia incidence declined in African-Americans but not in Yoruba.

INTRODUCTION: To compare dementia incidence of African-American and Yoruba cohorts aged ≥70 years enrolled in 1992 and 2001. METHODS: African-Americans residing in Indianapolis and Yoruba in Ibadan, Nigeria without dementia were enrolled in 1992 and 2001 and evaluated every 2-3 years until 2009. The cohorts consist of 1440 African-Americans, 1774 Yoruba in 1992 and 1835 African-Americans and 1895 Yoruba in the 2001 cohorts aged ≥70 years. RESULTS: In African-Americans, dementia and Alzheimer's disease (AD) incidence rates were significantly lower in 2001 than 1992 for all age groups except the oldest group. The overall standardized annual dementia incidence rates were 3.6% (95% confidence interval [CI], 3.2%-4.1%) in the 1992 cohort and 1.4% (95% CI, 1.2%-1.7%) in the 2001 cohort. There was no significant difference in dementia or AD incidence between the Yoruba cohorts. DISCUSSION: Future research is needed to explore the reasons for the differential changes in incidence rates in these two populations.