Prevalence of Alzheimer's disease and dementia in two communities: Nigerian Africans and African Americans.
Level 4 - case-series / case-control
Cross-sectional comparative epidemiological prevalence study
PubMed 7573588 · doi:10.1176/ajp.152.10.1485
What was done
A two-stage prevalence study compared dementia and Alzheimer's disease rates in adults aged 65 and older from two genetically related populations living in different environments: Yoruba residents in Ibadan, Nigeria (n = 2,494) and African American residents in Indianapolis, Indiana (n = 2,212 community-dwelling, n = 106 in nursing homes; total n = 2,318). Both sites utilized identical methodology involving an initial cognitive screening stage followed by clinical diagnostic assessment for selected participants based on screening performance.
What was found
Age-adjusted prevalence of dementia was 2.29% in Ibadan compared to 4.82% in Indianapolis community-dwelling subjects and 8.24% in the combined Indianapolis sample. Age-adjusted Alzheimer's disease prevalence was 1.41% in Ibadan compared to 3.69% in community-dwelling Indianapolis residents and 6.24% in the combined Indianapolis sample. All differences between Ibadan and Indianapolis were statistically significant. Prevalence rates increased consistently with advancing age in both cohorts.
Why it matters
Demonstrating substantially lower dementia and Alzheimer's disease rates in native Nigerian Africans compared to African Americans sharing similar ancestral lineage strongly implicates environmental, dietary, or lifestyle factors in the etiology of Alzheimer's disease.
Limits
The cross-sectional design cannot establish causal mechanisms or account for potential survival bias (differential mortality prior to age 65 across sites). The abstract does not report confidence intervals, specific environmental risk exposures, or potential cultural and educational biases in the screening instruments.
Cited by
- supports Studies of indigenous hunter-gatherer populations like the Hadza in Tanzania and rural agrarian groups like the Yoruba find that Alzheimer's and vascular dementia are exceptionally rare.