Incidence of dementia and Alzheimer disease in 2 communities: Yoruba residing in Ibadan, Nigeria, and African Americans residing in Indianapolis, Indiana.
Level 3 - non-randomized controlled study
Prospective population-based comparative cohort study
PubMed 11176911 · doi:10.1001/jama.285.6.739
What was done
The Indianapolis-Ibadan Dementia Project prospectively followed two community-dwelling cohorts aged 65 years or older without dementia at baseline (1992–1993): 2,459 Yoruba residents of Ibadan, Nigeria, and 2,147 African American residents of Indianapolis, Indiana. Participants were assessed across two follow-up waves at 2 years (1994–1995) and 5 years (1997–1998), with mean follow-up times of 5.1 and 4.7 years, respectively. Both sites used an identical two-stage design comprising an in-home screening interview followed by a comprehensive diagnostic workup in a subsample selected based on screening performance, evaluated by the same group of investigators.
What was found
Age-standardized annual incidence rates were significantly lower in Yoruba participants than in African American participants: - Dementia: 1.35% (95% CI, 1.13%–1.56%) in Yoruba vs 3.24% (95% CI, 2.11%–4.38%) in African Americans. - Alzheimer disease: 1.15% (95% CI, 0.96%–1.35%) in Yoruba vs 2.52% (95% CI, 1.40%–3.64%) in African Americans.
Why it matters
This study provides the first direct comparison of dementia and Alzheimer disease incidence between an industrialized and a developing country using identical harmonized diagnostic criteria. The markedly lower rates in Ibadan suggest that environmental, lifestyle, or gene-environment factors play a major role in dementia risk.
Limits
The two-stage screening and diagnostic approach could introduce cultural or educational test-performance biases despite harmonization. The abstract reports crude/age-standardized rates without adjustment for potential confounding variables such as baseline vascular disease, education, or competing mortality differences between sites. Generalizability beyond these two specific urban communities is uncertain.
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.