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.