Anemia is a condition in which the body does not have enough healthy red blood cells. Red blood cells provide oxygen to body tissues. There are many types of anemia.

Vitamin B12 deficiency anemia is a low red blood cell count due to a lack of vitamin B12.

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 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 level 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

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.

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

• Treatment may include a shot of vitamin B12 once a month. Persons with a severely low level 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 disease, celiac disease, or alcoholism is properly treated.

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

Patients often do well with treatment.

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.

A woman with a low B12 level may have a false positive Pap smear. This is because vitamin B12 deficiency affects the way certain cells (epithelial cells) in the cervix 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 a low vitamin B12 level.

Antony AC. Megaloblastic anemias. In: Hoffman R, Benz EJ Jr, Silberstein LE, et al., eds. Hematology: Basic Principles and Practice. 6th ed. Philadelphia, Pa: Elsevier Saunders; 2012:chap 37.