The impact of diabetes mellitus on the development of psychiatric and neurological disorders

Diabetes mellitus (DM) is a chronic condition resulting from insulin deficiency or systemic insulin resistance. In this disorder, either the pancreatic β-cells are unable to produce enough insulin, or the secreted insulin is ineffective to overcome the peripheral or central insulin resistance. Over time, glucose metabolism becomes dysregulated, resulting in overt DM characterized by hyperglycemia and chronic systemic inflammation. This research review explores the connections and potential correlations between DM and various psychiatric and neurological disorders, including major depressive disorder (MDD), Parkinson's disease (PD), and Alzheimer's disease (AD). While no claims of direct causation can be made, DM does show significant correlations and associations with MDD, PD, and AD. Each of these conditions shows some overlap among risk factors, biological pathways, mechanisms, and therapeutic approaches with DM. Interestingly, depending on the factor, DM can influence the progression of MDD, PD and AD, and vice versa. This review of pathophysiological pathways and molecular events associated with these disorders allows for further investigation into establishing connections between each of these conditions.