 Vitamin B12 plays an important role in DNA synthesis and neurological function. Its deficiency is associated with hematological, neurological and psychiatric manifestations of which the latter include irritability, personality change, depression, dementia and rarely, psychosis. Recent literature has seen links between this vitamin and depression. High B12 levels in serum are associated with good treatment response, high homocysteine levels are common in folate B12 deficiency and in those suffering from depression. Hyperhomocysteinemia may have direct effects on neurotransmitters implicated in depression. 