Cognitive Reserve, Incident Dementia, and Associated Mortality in the Ibadan Study of Ageing

Abstract

Objectives: To describe factors associated with incident dementia and dementia mortality over 5 years in a large community sample of elderly persons.

Design: Longitudinal investigation of a household multistage probability sample.

Setting: Eight contiguous states of the Yoruba-speaking region of Nigeria.

Participants: Individuals aged 65 and older (N = 2,149).

Measurements: Dementia was diagnosed using tools previously validated in the population. Incident cases of dementia over three follow-up waves were determined after censoring cases in the preceding wave. Information on mortality was collected from key informants in subjects' households.

Results: A dementia incident rate was found of 20.9 per 1,000 person-years (95% confidence interval (CI) = 17.7-24.9). The adjusted mortality hazard for those with dementia was 1.5 (95% CI = 1.1-2.1). Along with previously identified social and demographic factors, poor predementia cognitive function (hazard ratio (HR) = 1.8, 95% CI = 1.1-2.8) and low occupational complexity (HR = 3.2, 95% CI = 1.3-8.0) were associated with incident dementia.

Conclusion: The findings confirm the low incidence of dementia in this population, as previously reported. The condition is nevertheless associated with higher risk of mortality. Along with some features of social disadvantage, proxies of lower cognitive reserve were risk factors for incident dementia.

Keywords: dementia; epidemiology; low- and middle-income countries; mortality; risk factors.