Ogunniyi A, Hall KS, Gureje O, Baiyewu O, Gao S, Unverzagt FW, Smith-Gamble V, Evans RE, Dickens J, Musick BS, Hendrie HC. Risk factors for incident Alzheimer's disease in African Americans and Yoruba. Metab Brain Dis. 2006 Sep;21(2-3):235-40. Epub 2006 Jul 19.

INTRODUCTION: The incidence rate of Alzheimer's disease (AD) was found to be 2 times lower in Yoruba than in African Americans. This study was aimed at identifying the factors associated with increased risk of incident AD in the two communities. METHODOLOGY: A two-stage design with initial screening using the CSI'D followed by neuropsychological test battery, relations' interview and physician assessment in a sub-sample.NINCDS-ADRDA criteria were met for AD. The risk factor variables assessed included demographic, lifestyle, medical and family history items. RESULTS: In the Yoruba, AD was associated with age (OR = 1.07) and female gender (OR = 2.93). In African Americans, age (OR = 1.09) and rural living (OR = 2.08) were the significant risk factors, while alcohol was protective (OR = 0.49). DISCUSSION: Age was a significant risk factor for AD at both sites. The higher risk of incident AD in the Yoruba female, and in African Americans who resided in rural areas in childhood were similar with the prevalence cases. Alcohol emerged a protective factor in African Americans. More studies are required, including biological measurements, to adequately explain the differences in rates.

Hendrie HC, Ogunniyi A, Hall KS, Baiyewu O, Unverzagt FW, Gureje O, Gao S, Evans RM, Ogunseyinde AO, Adeyinka AO, Musick B, Hui SL. Incidence of dementia and Alzheimer disease in 2 communities: Yoruba residing in Ibadan, Nigeria, and African Americans residing in Indianapolis, Indiana. JAMA. 2001 Feb 14;285(6):739-47.

CONTEXT: Alzheimer disease (AD) represents a major and increasing public health problem. If populations were identified with significantly lower or higher incidence rates of AD, the search for risk factors in the genesis of AD could be greatly enhanced. OBJECTIVE: To compare incidence rates of dementia and AD in 2 diverse, elderly community-dwelling populations. DESIGN: The Indianapolis-Ibadan Dementia Project, a longitudinal, prospective population-based study consisting of a baseline survey (1992-1993) and 2 subsequent follow-up waves after 2 years (1994-1995) and 5 years (1997-1998). Each wave followed a 2-stage design, with an in-home screening interview followed by a full diagnostic workup of a subsample of participants based on screening performance. SETTING AND PARTICIPANTS: A total of 2459 community-dwelling Yoruba residents of Ibadan, Nigeria, without dementia, and 2147 community-dwelling African American residents of Indianapolis, Ind, without dementia (all aged 65 years or older). The cohorts were followed up for a mean of 5.1 years and 4.7 years, respectively. MAIN OUTCOME MEASURES: Incident cases of dementia and AD in each of the 2 populations. RESULTS: The age-standardized annual incidence rates were significantly lower among Yoruba than among African Americans for dementia (Yoruba, 1.35% [95% confidence interval [CI], 1.13%-1.56%]; African Americans, 3.24% [95% CI, 2.11%-4.38%]) and for AD (Yoruba, 1.15% [95% CI, 0.96%-1.35%]; African Americans, 2.52% [95% CI, 1.40%-3.64%]). CONCLUSION: This is the first report of incidence rate differences for dementia and AD in studies of 2 populations from nonindustrialized and industrialized countries using identical methods and the same group of investigators in both sites. Further explorations of these population differences may identify potentially modifiable environmental or genetic factors to account for site differences in dementia and AD.

Hall K, Gureje O, Gao S, Ogunniyi A, Hui SL, Baiyewu O, Unverzagt FW, Oluwole S, Hendrie HC. Risk factors and Alzheimer's disease: a comparative study of two communities. Aust N Z J Psychiatry. 1998 Oct;32(5):698-706.

OBJECTIVE: To determine the association between demographic, lifestyle and medical history factors to Alzheimer's disease (AD), we studied samples of two community dwelling populations with significantly different prevalence rates of AD in Indianapolis, USA (6.24%) and Ibadan, Nigeria (1.4%). METHODS: The samples were drawn from African-American community dwelling residents 65 years of age and over in Indianapolis, and Yoruba community-dwelling residents 65 years of age and over in Ibadan. A two-stage epidemiological design was used in which diagnosis of AD was by National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association criteria. RESULTS: In Indianapolis, age (odds ratio [OR] = 1.16; 95% confidence interval [CI] = 1.11-1.21), family history of dementia (OR = 5.40; 95% CI = 1.99-14.62), low education (0-6 years, OR = 3.49; 95% CI = 1.06-11.48) and rural residence (OR = 2.49; 95% CI = 1.05-5.88) were associated with a higher risk of AD. In Ibadan, age (OR = 1.15; 95% CI = 1.12-1.18) and female gender (OR = 13.9; 95% CI = 3.85-50.28) were associated with a higher risk of AD. CONCLUSIONS: The remarkably similar odds ratios between age and AD between sites suggest that biological processes associated with ageing are essential elements in the development of AD but that genetic and environmental risk factors may alter age-specific rates. In our longitudinal study, we intend to investigate in more depth the interaction between these ageing, genetic and environmental factors.

Ogunniyi A, Gureje O, Baiyewu O, Unverzagt F, Hall KS, Oluwole S, Osuntokun BO, Hendrie HC. Profile of dementia in a Nigerian community--types, pattern of impairment, and severity rating. J Natl Med Assoc. 1997 Jun;89(6):392-6.

Out of 2494 subjects screened in a Nigerian community, 28 patients with dementia were identified. Alzheimer's disease was diagnosed in 18 patients (64.3%), 16 of whom had probable Alzheimer's disease. Eight patients (28.6%) had vascular dementia while one patient each had parkinsonism with dementia and depression with dementia. Patients with Alzheimer's disease were significantly older, predominantly females and illiterates. Cognitive deficit commonly took the form of memory and judgment impairment while financial mismanagement was the most frequent impaired activity of daily living. More than half of the cases had mild disease on severity rating and were comprised mainly of Alzheimer's disease subjects. These results confirm the higher frequency of Alzheimer's disease over the other types as reported in other communities.

Hendrie HC, Osuntokun BO, Hall KS, Ogunniyi AO, Hui SL, Unverzagt FW, Gureje O, Rodenberg CA, Baiyewu O, Musick BS. Prevalence of Alzheimer's disease and dementia in two communities: Nigerian Africans and African Americans. Am J Psychiatry. 1995 Oct;152(10):1485-92.

OBJECTIVE: This article reports on a prevalence study of dementia and Alzheimer's disease among two groups of subjects with the same ethnic background but widely differing environments. METHOD: The study was conducted among residents aged 65 years and older in two communities: Yorubas (N = 2,494) living in Ibadan, Nigeria, and African Americans (N = 2,212 in the community and N = 106 in nursing homes) living in Indianapolis, Indiana. The study design consisted of a screening stage followed by a clinical assessment stage for selected subjects on the basis of their performance on the screening tests. RESULTS: The age-adjusted prevalence rates of dementia (2.29%) and Alzheimer's disease (1.41%) in the Ibadan sample were significantly lower than those in the Indianapolis sample, both in the community-dwelling subjects alone (4.82% and 3.69%, respectively) and in the combined nursing home and community samples (8.24% and 6.24%, respectively). The prevalence rates of dementia and Alzheimer's disease increased consistently with advancing age in both study groups. CONCLUSIONS: To the authors' knowledge, this is the first study, using the same research method at the two sites, to report significant differences in rates of dementia and Alzheimer's disease in two different communities with similar ethnic origins.

Osuntokun BO, Ogunniyi AO, Lekwauwa UG. Alzheimer's disease in Nigeria. Afr J Med Med Sci. 1992 Dec;21(2):71-7.

The age-related dementias of the elderly (those aged 65 years or more) are of major public health importance in developed countries. Developing countries, most of which are undergoing epidemiological transition and greying of population, currently contain more than half of the world's population of elderly, a proportion that would reach 75% by 2020. Apart from reports from China, there is little or no information on the dementias of the elderly in developing countries. Alzheimer's disease, which accounts for two-thirds of dementia of the elderly in Caucasian population, is under-documented and believed to be rare in black Africans. But black Americans who are of black African lineage commonly suffer from Alzheimer's disease. A recent autopsy survey of the brains of elderly Nigerians showed absence of senile plaques and neurofibrillary tangles, the pathognomonic histologic lesions of Alzheimer's disease and ageing found in 25% to 80% of normal undemented elderly Caucasians and Japanese. In a community-based door-to-door survey of a population of 9000, including 932 elderly Nigerians, no subject with dementia as defined by DSM-IIIR was found, although there was significant decline of cognition with age, female sex and less than 6 years of formal education. The distribution of cognitive scores is a highly skewed unimodal curve. We emphasize the potential value of cross-cultural epidemiological studies of ethnic groups in different environments and with different prevalence ratios of Alzheimer's disease, in identifying putative environmental factors for this disease.