Your body uses vitamin B12 to make red blood cells and to keep your nerve cells healthy. Vitamin B12 deficiency occurs when your body does not contain adequate amounts of the vitamin, and as a result red blood cells do not form properly. A prolonged vitamin B12 deficiency can lead to nerve damage, which is usually permanent.
Physiology
Without adequate amounts of vitamin B12, red blood cells do not divide normally. As a result, the red blood cells become too large, a condition called macrocytic or pernicious anemia. Because the red blood cells are larger than normal, they do not travel through your body correctly and have difficulty traveling out of the bone marrow in which they are made. If red blood cells cannot leave the bone marrow, they cannot deliver oxygen to or remove carbon dioxide from your body tissues.
Causes
Your body needs a protein called intrinsic factor to properly absorb vitamin B12. One of the most common causes of a vitamin B12 deficiency is a lack of intrinsic factor. Without intrinsic factor, you cannot absorb vitamin B12, regardless of the amount of the vitamin you consume.
Vitamin B-12 deficiency may also develop as a result of intestinal disorders that interfere with the absorption of vitamin B-12, such as Crohn's disease or celiac disease, or certain medications that cause decreased absorption.
A lack of vitamin B12 in the diet may also lead to vitamin B-12 deficiency, but the National Heart, Lung and Blood Institute notes that this is the least common cause. Strict vegetarians and vegans are at the highest risk of developing deficiency from a lack of vitamin B-12 in the diet.
Symptoms
Because red blood cells deliver oxygen and vitamin B12 deficiency is characterized by a lack of red blood cells, the first symptom of pernicious anemia is usually fatigue due to lack of oxygen. The low red blood cell count is also responsible for dizziness, shortness of breath, chest pain, coldness in the hands and feet and pale skin and gums.
If vitamin B12 deficiency is not corrected early, it can lead to nerve damage that presents as tingling and numbness in the hands and feet, loss of balance, difficulty walking, muscle weakness and loss of reflexes.
Treatment
Treatment for vitamin B12 deficiency depends on the cause. If anemia develops because of a lack of intrinsic factor or malabsorption in the small intestine, no amount of oral vitamin supplementation will correct the condition. Intravenous vitamin B12 is necessary to correct this type of deficiency. Intravenous injections allow vitamin B12 to surpass the stomach and enter the bloodstream directly.
If a vitamin B12 deficiency develops due to a lack of dietary vitamin B12, oral supplements or an increase in vitamin B12 in the diet are usually sufficient to correct the condition.
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