In patients with DM and depressive disorders, a wide variety of disturbances may affect the central nervous systems, including the overactivation of the HPA axis, decreased monoamine neurotransmitters, and dysfunctional brain-derived neurotrophic factor (BDNF) (Donato, 2012; Biessels and Reijmer, 2014). Here, BDNF is linked to depressive disorder.