Incidence and risk factors for late-life depression in the Ibadan Study of Ageing.

Background: We present the incidence and risk factors for major depressive disorder (MDD) among community-dwelling elderly Nigerians.

Method: A cohort study of persons aged ≥ 65 years residing in eight contiguous Yoruba-speaking states in south-west and north-central Nigeria was conducted between November 2003 and December 2007. Of the 2149 baseline sample, 1408 (66%) were successfully followed up after approximately 39 months. Face-to-face in-home assessments were conducted with the World Health Organization (WHO) Composite International Diagnostic Interview, version 3 (CIDI.3) and diagnosis was based on the DSM-IV. Incident MDD was determined in the group with no prior lifetime history of MDD at baseline and who were free of dementia at follow-up (n=892).

Results: During the follow-up period, 308 persons had developed incident MDD, representing a rate of 104.3 [95% confidence interval (CI) 93.3-116.6] per 1000 person-years. Compared to males, the age-adjusted hazard for females was 1.63 (95% CI 1.30-2.06). Lifetime or current subsyndromal symptoms of depression at baseline did not increase the risk of incident MDD. Among females, but not males, rural residence and poor social network were risk factors for incident MDD. Physical health status at baseline did not predict new onset of MDD.

Conclusions: The finding of a high incidence of MDD among elderly Nigerians complements earlier reports of a high prevalence of the disorder in this understudied population. Social factors, in particular those relating to social isolation, constitute a risk for incident MDD.