Type 2 diabetes mellitus as a risk factor for the onset of depression: a systematic review and meta-analysis

Abstract

Aims/hypothesis: An earlier meta-analysis showed that diabetes is a risk factor for the development and/or recurrence of depression. Yet whether this risk is different for studies using questionnaires than for those relying on diagnostic criteria for depression has not been examined. This study examined the association of diabetes and the onset of depression by reviewing the literature and conducting a meta-analysis of longitudinal studies on this topic.

Methods: EMBASE, MEDLINE and PsycInfo were searched for articles published up to September 2009. All studies that examined the relationship between type 2 diabetes and the onset of depression were included. Pooled relative risks were calculated using fixed and random effects models.

Results: Eleven studies met our inclusion criteria for this meta-analysis. Based on the pooled data, including 48,808 cases of type 2 diabetes without depression at baseline, the pooled relative risk was 1.24 (95% CI 1.09-1.40) for the random effects model. This risk was significantly higher for studies relying on diagnostic criteria of depression than for studies using questionnaires. However, this difference was no longer significant when controlled for year of publication.

Conclusions/interpretation: Compared with non-diabetic controls, people with type 2 diabetes have a 24% increased risk of developing depression. The mechanisms underlying this relationship are still unclear and warrant further research.

Fig. 1

Forest plots showing the OR of depression in type 2 diabetes for individual studies using depression self-report questionnaires, diagnostic criteria, and all studies combined. Bars and diamonds indicate 95% CIs. The size of each square corresponds to the weight of the study in the meta-analysis. D + L, random-effects estimate (Der Simonian and Laird method); I–V, fixed-effects estimate (inverse variance method)

Fig. 2

Begg’s funnel plot with pseudo 95% CI of all the studies included in the meta-analysis