Depression is a frequent co morbidity of type 2 diabetes potentially because of the risk factors. Several studies had shown that depression, even at subclinical levels, increases the risk of incident type 2 diabetes by 25–60%.

      Researchers from the University of Surrey explored the genetic affinities and causal links between depression and type 2 diabetes. To find out whether type 2 diabetes and depression could contribute to the development of one another, researchers used two-sample bi-directional Mendelian randomization (MR) approach. the genetic and health information of 19,344 people with type 2 diabetes, more than 5,000 people who had been diagnosed with depression, and 153,079 people who self-reported depression were examined.

      MR demonstrated a significant causal effect of depression on type 2 diabetes (odds ratio 1.26 [95% CI 1.11–1.44], P = 5.46 × 10−4) but not in the reverse direction. Also, the Mediation analysis indicated that 36.5% of the effect from depression on type 2 diabetes was mediated by BMI. The researchers not only identified seven genetic variants contributing to both type 2 diabetes and depression but also highlighted their importance in understanding the link between these conditions.  The shared genes play a role in insulin secretion or inflammation in the brain, pancreas, or fat tissue, with changes in these biological processes potentially explaining how depression increases risk of type 2 diabetes.

      The research showed, for the first time a "significant causal effect" between depression and an elevated risk of type 2 diabetes. The investigation team again pinpointed that higher body weight contributed to, but did not fully account for, the impact of depression on type 2 diabetes.