Vitamin B12 deficiency anemia

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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 (deficiency) of vitamin B12.

Alternative Names

Megaloblastic 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 poorly planned 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
  • Surgery that removes 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:

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

Exams and Tests

The health care provider will perform a physical exam. This may reveal problems with your reflexes.

Tests that may be done include:

Other procedures that may be done include:


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. If you have a very low level of B12, you may need more shots in the beginning. It is possible you may need shots every month for the rest of your life.
  • Some people may also need to take vitamin B12 supplements by mouth.

Treatment may no longer be needed after Crohn disease, celiac disease, or alcohol use is properly treated.

Your provider will also recommend that you eat a variety of foods.

Outlook (Prognosis)

People with this type of anemia 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.

Possible Complications

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.

When to Contact a Medical Professional

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


You can prevent anemia caused by a lack of vitamin B12 by eating 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; 2013:chap 37.

Bunn HF. Approach to the anemias. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 158.

Version Info

  • Last reviewed on 2/1/2016
  • Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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