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Vitamin Deficiency Anemia

by Alan E. Lichtin, MD

Vitamin deficiency anemia results from low or depleted levels of vitamin B 12 or folate (folic acid).

  • People may be weak, short of breath, and pale.

  • Nerves may also malfunction.

  • Blood tests can detect abnormal cells that indicate vitamin deficiency anemia.

  • The deficient vitamin is replaced.

Vitamin B 12 deficiency and folate (folic acid) deficiency cause megaloblastic anemia. In megaloblastic anemia, the bone marrow produces red blood cells that are large and abnormal (megaloblasts).

Deficiency of vitamin B 12 (see Vitamin B 12 Deficiency) or folate (see Folate Deficiency) most often develops due to a lack of these vitamins in the diet or an inability to absorb these vitamins from the digestive tract. Deficiency of these vitamins is sometimes caused by drugs used to treat cancer, such as methotrexate, hydroxyurea, fluorouracil, and cytarabine.

Symptoms and Diagnosis

Symptoms of anemia due to vitamin B 12 or folate deficiency develop slowly and are similar to symptoms caused by other types of anemia, such as fatigue, weakness, and paleness. Vitamin B 12 deficiency can also cause nerves to malfunction, causing tingling, loss of sensation, and muscle weakness (see Vitamin B 12 Deficiency). Severe vitamin B 12 deficiency may cause confusion. Folate deficiency may cause diarrhea and may cause the tongue to swell.

Once blood tests show a person has anemia, tests are done to determine if a deficiency of vitamin B 12 or folate is the cause. Anemia due to vitamin B 12 or folate deficiency is suspected when megaloblasts are seen in a blood sample that is examined under a microscope. Changes in white blood cells and platelets also can be detected, especially when people have had megaloblastic anemia for a long time.

The blood levels of vitamin B 12 and folate are measured, and other tests may be done to determine the cause of the vitamin deficiency.


The treatment of anemia due to vitamin B 12 or folate deficiency consists of replacing the deficient vitamin.

Commonly, vitamin B 12 is administered by injection, particularly when the deficiency is severe or caused by an inability to absorb the vitamin from the digestive tract. At first, injections are given daily or weekly for several weeks until the blood levels of vitamin B 12 return to normal. Then injections are given once a month. Vitamin B 12 can also be taken daily as a nose spray, a tablet placed under the tongue, or a tablet that is swallowed. People who have anemia due to vitamin B 12 deficiency usually must take vitamin B 12 supplements for life.

Folate can be taken as one tablet daily. People who have trouble absorbing folate take supplements for life.

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