Vitamin B12 deficiency anemia is a low red blood cell count due to a lack of vitamin B12.  Anemia is a condition in which the body does not have enough healthy red blood cells. Red blood cells provide oxygen to body tissues.

See also:

• Megaloblastic anemia
• Pernicious anemia

Macrocytic anemia

Your body needs vitamin B12 to make red blood cells. In order to provide vitamin B12 to your cells:

• You must eat plenty of foods that contain vitamin B12, such as meat, poultry, shellfish, eggs, and dairy products.
• Your body must absorb enough vitamin B12. A special protein, called intrinsic factor, helps your body do this. This protein is released by cells in the stomach.

A lack of vitamin B12 may be due to dietary factors, including:

• Eating a vegetarian diet
• Poor diet in infants
• Poor nutrition during pregnancy

Certain health conditions can make it difficult for your body to absorb enough vitamin B12. They include:

• Chronic alcoholism
• Crohn's disease, celiac disease, infection with the fish tapeworm, or other problems that make it difficult for your body to digest foods
• Pernicious anemia, a type of vitamin B12 anemia that occurs when your body destroys cells that make intrinsic factor
• Surgeries that remove certain parts of your stomach or small intestine, such as some weight-loss surgeries
• Taking antacids and other heartburn medicines for a long period of time

You may not have symptoms. Symptoms may be mild.

Symptoms can include:

• Diarrhea or constipation
• Fatigue, lack of energy, or light-headedness when standing up or with exertion
• Loss of appetite
• Pale skin
• Problems concentrating
• Shortness of breath, mostly during exercise
• Swollen, red tongue or bleeding gums

If you have low vitamin B12 levels for a long time, you can have nerve damage. Symptoms of nerve damage include:

• Confusion or change in mental status (dementia) in severe cases
• Depression
• Loss of balance
• Numbness and tingling of hands and feet

The doctor or nurse will perform a physical exam. This may reveal problems with your reflexes.

Tests that may be done include:

• Complete blood count (CBC)
• Reticulocyte count
• LDH level
• Vitamin B12 level 

This list may not be all-inclusive.

Other procedures that may be done include: 

• Esophagogastroduodenoscopy (EGD) to examine the stomach
• Enteroscopy to examine the small intestine
• Bone marrow biopsy if the diagnosis is not clear

Treatment depends on the cause of B12 deficiency anemia. For treatment of anemia due to a lack of intrinsic factor, see: Pernicious anemia

The goal of treatment is to increase your vitamin B12 levels.

• Treatment may include a shot of vitamin B12 once a month. Persons with severely low levels of B12 may need more shots in the beginning. You may need shots every month for the rest of your life.
• Some patients may also need to take vitamin B12 supplements by mouth. For some people, high-dose vitamin B12 tablets taken by mouth work well, and shots are not needed.

 Treatment may no longer be needed after Crohn's disease, celiac disease, or alcoholism is properly treated.

Your doctor or nurse will also recommend eating a well-balanced diet.

With treatment, patients usually do well.

Long-term vitamin B12 deficiency can cause nerve damage. This may be permanent if you do not start treatment within 6 months of when your symptoms begin.

Women with low B12 levels may have a falsely abnormal Pap smear. That is because vitamin B12 affects the way certain cells, called epithelial cells, look.

Call your health care provider if you have any of the symptoms of anemia.

You can prevent anemia caused by a lack of vitamin B12 by following a well-balanced diet.

Shots of vitamin B12 can prevent anemia after surgeries known to cause vitamin B12 deficiency.

Early diagnosis and prompt treatment can reduce or prevent complications related to low vitamin B12 levels.

Antony AC. Megaloblastic anemias. In: Goldman L, Schafer AI, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 2011:chap 167.