Vitamin B₁₂ deficiency is a leading cause of megaloblastic anemia and can occur at any age. The mechanism of vitamin B₁₂ transport is a rather complicated process; failure of any of its stages leads to loss of absorption of vitamin B₁₂ and, consequently, to the development of B₁₂-deficient states. There are many known causes of B₁₂ deficiency, which range from severe to mild. Mild deficiencies are usually due to dietary errors. Severe B₁₂ deficiency resulting from the failure of the gastric or ileal phase of physiological absorption of the vitamin leads to pernicious anemia. Failure to diagnose B₁₂ deficiency can have overall health consequences ranging from mild to severe, as well as complications for many body systems and functions, including the cardiovascular system.