B 12 is an essential vitamin for human body which reduces the chances of neurological diseases, birth defects, and chronic disorders. It is a vital micro-nutrient for maintaining the brain health. This review sorts out some causes of vitamin B 12 (B 12) deficiency and develops its link with neurological disorders. The portals include PubMed, Google Scholar, Directory of Open Access Journals (DOAJ), Pak MediNet, and Science Direct were search for literature retrieval. Study of literature revealed that deficiency of this vitamin occurs primarily due to insufficient dietary intake which results in a group of neurological symptoms in adults as well as infants. These neurological disorders include apathy, anorexia, irritability, growth retardation, and developmental regression. It may also involve in delayed myelination or demyelination of neurons. It was concluded that B 12 is vital micro-nutrient for healthy brain in children, younger, and elders. Various conditions are responsible for deficiency of B 12. A timely and proper supplementation is necessary if it is dietary deficiency.