Diabetes and the Nervous System: Linking Peripheral Neuropathy to Central Neurodegeneration.

Diabetes mellitus affects both the peripheral and central nervous systems, giving rise to a spectrum of neurological complications that extend far beyond the traditional focus on diabetic peripheral neuropathy (DPN). Chronic hyperglycemia disrupts cellular homeostasis through increased formation of advanced glycation end-products, activation of inflammatory pathways, mitochondrial dysfunction, oxidative stress, and impaired neurovascular regulation. These disturbances converge to drive axonal degeneration, demyelination, synaptic injury, and progressive cognitive decline. Emerging evidence also highlights a critical role for gut dysbiosis and intestinal barrier dysfunction, which facilitate microbial translocation and systemic inflammation, ultimately disrupting the blood-brain barrier and amplifying neuroimmune injury. This narrative review synthesizes current mechanistic, clinical, and translational insights into how metabolic, inflammatory, vascular, and microbial pathways interact to produce diabetes-associated neurodegeneration. We summarize key molecular drivers-including mitochondrial ROS overproduction, microglial and astrocytic activation, endothelial dysfunction, and insulin resistance-while also describing their contributions to DPN, autonomic neuropathy, and diabetes-related cognitive impairment. We further integrate evidence from emerging therapeutic domains, including mitochondrial stabilizers, anti-inflammatory strategies, gut-microbiome modulation, and neurovascular-targeted interventions. Despite advances in understanding, disease-modifying therapies remain limited, and diagnostic tools for early detection are underutilized. Bridging these gaps will require longitudinal human studies, improved biomarkers, and integrative therapeutic approaches that target multiple convergent pathways. A deeper understanding of cross-talk among metabolic, immune, vascular, and microbial systems may enable earlier intervention and more effective strategies to mitigate the neurological burden of diabetes.