Vitamin B12 is necessary for hematopoiesis and normal neuronal function. B12 deficiency may be due to lack of intrinsic factor secretion by gastric mucosa (gastrectomy, gastric atrophy) or intestinal malabsorption (ileal resection, small intestinal disease.Vitamin B12 deficiency frequently causes macrocytic anemia, glossitis, peripheral neuropathy, weakness, hyperreflexia, ataxia, loss of proprioception, poor coordination, and affective behavioral changes. These manifestations may occur in any combination; many patients have the neurologic defects without macrocytic anemia.