Depression and diabetes are among the most prevalent morbidities worldwide, with prevalences expected to rise. For type 2 diabetes and depression a bi-directional association has been often described. This association may be driven by suboptimal blood glucose levels, although studies investigating associations between depression and HbA1c levels have resulted in inconsistent findings. Additionally, these data are mostly based on cross-sectional studies and the most recent meta-analysis was performed more than 20 year ago. More recently, a meta-analysis showed the reverse association, between HbA1c and depression, for people with previously diagnosed diabetes (but not for newly diagnosed diabetes or impaired glucose metabolism). However, this study lacked sufficient power.
In this systematic review and meta-analysis, in which Giesje Nefs of Diabeter was involved, studies reporting longitudinal data were collected to investigate associations between depression and HbA1c levels and vice versa. It was hypothesized that increased levels of HbA1c result in a higher risk for depression and vice versa.
In addition to the strengths of this study (comprehensive search including four databases, addressing both directions of the association between depression and HbA1c, inclusion of papers in multiple languages and of longitudinal studies), a few important limitations should be mentioned:
Concluding, the authors state