Merck Manual

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Vitamin Deficiency Anemia

(Megaloblastic Anemia)


Evan M. Braunstein

, MD, PhD, Johns Hopkins University School of Medicine

Reviewed/Revised Jul 2022 | Modified Sep 2022

Vitamin deficiency anemia results from low or depleted levels of vitamin B12 or folate (folic acid).

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

  • Nerves may malfunction.

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

  • The deficient vitamin is replaced.

Vitamin B12 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).

Symptoms of Vitamin Deficiency Anemia

Symptoms of anemia due to vitamin B12 deficiency or folate deficiency develop slowly and are similar to symptoms caused by other types of anemia, such as fatigue, weakness, and paleness. Vitamin B12 deficiency Vitamin B12 Deficiency Vitamin B12 deficiency can occur in vegans who do not take supplements or as a result of an absorption disorder. Anemia develops, causing paleness, weakness, fatigue, and, if severe, shortness... read more can also cause nerves to malfunction, causing tingling, loss of sensation, and muscle weakness. Severe vitamin B12 deficiency may cause confusion. In older people, anemia caused by vitamin B12 deficiency may be mistaken for dementia Dementia Dementia is a slow, progressive decline in mental function including memory, thinking, judgment, and the ability to learn. Typically, symptoms include memory loss, problems using language and... read more because of this symptom.

Diagnosis of Vitamin Deficiency Anemia

  • Blood tests

Once blood tests show a person has anemia, tests are done to determine if a deficiency of vitamin B12 or folate is the cause. Anemia due to vitamin B12 or folate deficiency is suspected when large (macrocytic) red blood cells and multilobed (hypersegmented) neutrophils (a type of white blood cell White Blood Cells The main components of blood include Plasma Red blood cells White blood cells Platelets read more White Blood Cells ) are seen in a blood sample that is examined under a microscope. Reduction in the number of white blood cells and platelets also can occur, especially when people have had vitamin deficiency anemia for a long time.

The blood levels of vitamin B12 and folate are measured, and other tests may be done to determine the cause of the vitamin B12 deficiency.

Treatment of Vitamin Deficiency Anemia

  • Replacement of vitamin B12 or folate

The treatment of anemia due to vitamin B12 deficiency or folate deficiency consists of replacing the deficient vitamin.

Commonly, vitamin B12 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 B12 return to normal. Then injections are given once a month. Vitamin B12 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 B12 deficiency may need to take vitamin B12 supplements for life.

Folic acid can be taken as one tablet daily.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Folacin , Folicet, Q-TABS
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