Knol MJ et al. (2006) Depression as a risk factor for the onset of type 2 diabetes mellitus. A meta-analysis. Diabetologia 49: 837–845

Evidence suggests that depression and diabetes are associated; however, it is unclear whether there is a temporal or causal relationship. Knol and colleagues, therefore, conducted a meta-analysis to examine whether depression is a risk factor for the onset of type 2 diabetes.

Nine studies were selected by the authors from MEDLINE and PsychINFO databases for inclusion in this meta-analysis. These were longitudinal studies, published before January 2005, that examined the link between depression and diabetes. Analysis revealed that adults with depression had a 37% increased risk of developing type 2 diabetes, compared with non-depressed individuals. Pathophysiologic mechanisms that could explain the increased risk of developing type 2 diabetes seen in depressed patients include increased levels of cortisol that could result in insulin resistance, dysregulation of the immune system, and low intake of ω-3 polyunsaturated fatty acids.

The authors conclude that depression is a risk factor for diabetes, but further studies are needed to establish the extent of this relationship. Obesity is the most important risk factor for the onset of type 2 diabetes, but Knol et al. consider that depression is a risk factor of comparable importance to smoking and physical inactivity. In addition, the authors believe that clinicians should be made aware of the association between depression and diabetes, as this link means that detection and treatment of depression becomes even more important than it is already.