Incidence of and Risk Factors for Dementia in the Ibadan Study of Aging

OBJECTIVES: To describe the incidence of dementia in a representative sample of elderly Yoruba Nigerians and provide information about the risk factors. DESIGN: In-home face-to-face assessments conducted on a community cohort selected using multistage clustered sampling of households, with baseline between November 2003 and August 2004 (n=2,149) and follow-up approximately 39 months later (n=1,408). SETTING: Eight contiguous, predominantly Yoruba-speaking states in Nigeria. PARTICIPANTS: Persons aged 65 and older free of dementia at baseline (n=1,225). MEASUREMENTS: Dementia was ascertained using two instruments: the 10-Word Delayed Recall Test and the Clinician Home-based Interview to assess Function, both with demonstrated validity and cultural applicability. RESULTS: At 3-year follow-up, 85 participants had developed dementia. With a total 3,888 risk years for the sample, the estimated incidence of dementia was 21.85 per 1,000 person-years (95% confidence interval=17.67-27.03). Compared with men, the age-adjusted hazard ratio (HR) for women was 2.12 (P=.002). Incidence increased linearly with age such that, compared with participant aged 65 to 74, the HR, adjusted for sex, for participants aged 75 to 84 was 2.84 (P<.001) and for those aged 85 and older was 4.13 (P<.001). Greater incidence of dementia was found with more-rural residence and poorer economic status. Participants with poor social engagement at baseline were at significantly greater risk of incident dementia. CONCLUSION: Incident dementia in Yoruba Nigerians is higher than previously reported. Indices of social isolation are risk factors for incident dementia in this population.