A lack of B12 damages the myelin sheath that protects nerves, causing those nerves cells to cease to function properly and leads to PN ("Nutritional Causes of Peripheral Neuropathy | Vitamin Deficiency Neuropathy", 2020). Application of B12 promotes the regeneration of myelinated nerve fiber and proliferation of Schwann cells. However, the neuropathy associated with impaired glucose tolerance (IGT) is clinically similar to early diabetic neuropathy, with preferential injury to small nerve fibers resulting in pain and autonomic dysfunction. Neuropathy develops when there is high blood glucose level, therefore disrupts normal nerve functioning. Hyperglycemia or high blood glucose also damages the blood vessels, including the small vessels that carry oxygen and nutrients to the nerves, especially the endings near hands and feet.