Vitamin B12 helps maintain healthy nerve cells and red blood cells. It is also needed to help make DNA, the genetic material in all cells. Vitamin B12 deficiency results from inadequate dietary intake or impaired absorption.
Vitamin B12 deficiency can be caused by inadequate dietary intake of vitamin B12, impaired absorption of vitamin B12, or intestinal parasites such as tape worm or giardiasis. Inability to absorb vitamin B12 from the intestinal tract can be caused by a disease known as pernicious anemia.
Vitamin B12 occurs naturally in animal products (eggs, meat, milk), so those with diets low in animal products are at-risk for vitamin B12 deficiency. However, the human body stores several years’ worth of vitamin B12, so nutritional deficiency of this vitamin is rare. Since it is only available in animal products, children with vegan diets may need supplementation.
The condition is commonly asymptomatic, but can also present with the following symptoms:
Loss of appetite
Sore mouth and tongue
Shortness of breath
Serious cases of vitamin B12 deficiency can cause damage to the nervous system, called subacute combined degeneration of the spinal cord, with the following symptoms:
Numbness and tingling of extremities
Vitamin B12 deficiency is a common cause of macrocytic anemia and has been implicated in a wide range of neuropsychiatric disorders. Vitamin B12 plays an important role in DNA synthesis and neurologic function. Deficiency can lead to hematologic and neuropsychiatric disorders that can often be reversed by early diagnosis and prompt treatment.
Vitamin B12 can be supplemented in healthy subjects by oral pills, sublingual pills, liquid, nasal sprays, or by injection. B12 is available singly or in combination with other supplements. Vitamin B12 can also be given as intramuscular injections.
Vitamin B12 is found in foods that come from animals, including fish, meat, poultry, eggs, milk, milk products, and fortified breakfast cereals.
In the developing world, Vitamin B12 deficiency is very widespread, with significant levels of deficiency in Africa, India, and South and Central America due to low intakes of animal products, particularly among the poor.