Brain-derived neurotrophic factor (BDNF) is a member of neurotrophin family associated with the proliferation, differentiation, activity-dependent plasticity, and survival of neurons in the central nervous system [1]. BDNF influences glucose metabolism and insulin sensitivity. For example, BDNF decreases serum glucose, insulin, and HbA1c levels in diabetic rats, suggesting that the BDNF may improve insulin sensitivity. In addition, animal models showed that BDNF levels in the central nervous system are highly related to peripheral serum BDNF levels [2]. It was found that BDNF may ameliorate glucose metabolism and prevent pancreatic exhaustion in obese diabetic mice [3].

Accumulating evidence has demonstrated that major depressive disorder (MDD) and Type 2 diabetes mellitus (T2DM) are two of the most prevalent and devastating diseases, and lead to considerable economic burden and loss of production labor. A substantial body of studies suggested that there is a strong link between depression and T2DM. For example, the prevalence of depression is increased significantly in patients with T2DM compared with those without diabetes [1]. In addition, depression appears to increase the prevalence of development of T2DM [2]. Hypotheses regarding the link between MDD and T2DM consist of physical and psychological factors. In spite of the evidence that depression is epidemiologically associated with T2DM, the cause of this correlation is still unclear.