A Guide to Megaloblastic Anemia

Medically Reviewed By Angelica Balingit, MD
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Megaloblastic anemia is a blood disorder in which your body has large, underdeveloped red blood cells. Low folic acid or vitamin B12 levels can cause megaloblastic anemia. Doctors typically diagnose it with a blood test and recommend a supplement schedule to help reduce the symptoms. 

Keep reading to learn more about megaloblastic anemia.

What is megaloblastic anemia?

a person is taking a vitamin
Sergey Narevskih/Stocksy United

Megaloblastic anemia is a blood disorder that causes large, partially developed red blood cells. These blood cells can die earlier than those with a normal life cycle. It makes it even harder for your body to maintain a proper red blood cell count. The most common cause of this type of anemia is inadequate vitamin B12 or folic acid.

Anemia is a common blood disorder in which your body has fewer red blood cells than it needs to function. Red blood cells are important because they carry oxygen through your blood vessels to your organs, tissues, and cells. Your body needs oxygen to create energy to carry out important tasks. Every time you run, jump, or digest food, your body uses oxygen. 

Learn more about low folate anemia.

What can cause megaloblastic anemia?

Folic acid or vitamin B12 deficiency can cause megaloblastic anemia. Folic acid is present in fruits, green vegetables, and meat. Spinach, asparagus, broccoli, peanuts, and sunflower seeds are all sources of folic acid. Sometimes, you may not be eating enough foods containing folic acid. Other times, your body may need more folic acid than it usually does. 

Some common causes of folic acid megaloblastic anemia are:

Animal products, including seafood, beef, chicken, eggs, and dairy, are the primary source of vitamin B12. Although a vegan diet that is not well-planned can cause vitamin B12 deficiency, pernicious anemia is the leading cause.

Pernicious anemia is an autoimmune disorder that prevents your body from absorbing vitamin B12 properly. If you have undergone a gastrectomy procedure to remove part of your stomach, you are more likely to develop vitamin B12 deficiency. 

Learn about pernicious anemia.


Some medications can limit the amount of vitamin B12 or folic acid your body absorbs. You can become deficient even if you have a diet rich in these vitamins because your body will not process them correctly. 

Some of these medications include:

Other medications cause megaloblastic anemia by affecting your bone marrow. Some medications that reduce the red blood cell production in your bone marrow include:

What are the signs and symptoms of megaloblastic anemia?

Megaloblastic anemia causes symptoms that progress slowly. You may not notice them right away, so it is important to be tuned in to subtle changes in your health. Overall, you may notice a lack of energy and headaches. You might also notice paleness, although this may be less obvious if you have dark skin. Other possible symptoms include:

If a vitamin B12 deficiency rather than a folic acid deficiency causes your megaloblastic anemia, you might experience other symptoms. These may include:

If you are consistently experiencing these symptoms, you should seek an appointment with a doctor. They can provide a diagnosis and treatment plan. 

Learn more about iron deficiency anemia.

How do doctors diagnose megaloblastic anemia?

A primary care physician or nurse practitioner should be able to diagnose you based on your symptoms and a blood test. During an office visit, the doctor will have you describe your symptoms. If they suspect megaloblastic anemia, they may recommend a blood test to confirm it. 

During a blood test, the doctor will take a small sample of your blood from a vessel in your arm. They will do this by cleaning the area, locating a suitable vein, inserting a needle, and using a syringe to draw up a small amount of blood. You may feel a pinch as the needle enters, but the test should not be painful. 

The blood sample will go to a laboratory where pathologists will test it for anemia. 

The laboratory team may check whether your red blood cells are unusually large. They may also test the levels of vitamin B12, folic acid, and hemoglobin.

If these levels are low, you may receive a diagnosis of megaloblastic anemia. 

How do doctors treat megaloblastic anemia?

After confirming the diagnosis, the doctor will establish a treatment plan to address your megaloblastic anemia. They may recommend oral folic acid or vitamin B12 supplements if your digestive tract is unaffected.

If you have a vitamin B12 deficiency resulting from a digestive issue, the doctor may recommend a vitamin B12 shot every couple of months. These injections may be necessary for the rest of your life. 

You may also need to adopt a diet rich in vitamin B12 or folic acid to address your deficiency. 

Foods rich in folic acid include:

  • asparagus
  • chickpeas
  • beans
  • brown rice

You can eat these foods to increase your vitamin B12 levels:

  • salmon
  • chicken
  • beef
  • milk
  • foods fortified with B12, including certain plant milks, soy products, and breakfast cereals

Changing your diet alone may not be enough to address your deficiency. Supplements and dietary changes may help you fix your low vitamin levels. 

Learn more about vitamin B12 deficiency and how to treat it.

What can follow-up care involve for megaloblastic anemia?

Follow-up care may be important for monitoring your folate and vitamin B12 levels. Your primary care physician may recommend periodic blood tests to check whether your treatment plan is effective. 

The first blood test may take place about 4 weeks after starting treatment. The doctor will take a sample of your blood to see whether there is an improvement. Your second blood test may take place at the 8-week mark. At about 4 months, your doctor may request another blood test to check your folic acid levels.

If these tests reveal no concerns, the doctor may recommend a yearly blood test going forward.

What is the outlook for megaloblastic anemia?

With proper supplementation, your vitamin levels should begin to stabilize in about 1 week. Your blood tests will show an increase in the number of red blood cells present within 2 months.

If you have depression, irritability, or any other mental health symptoms, it may take longer for you to notice a difference. These symptoms may take up to a year to resolve.

In some cases of severe vitamin deficiency, some symptoms may not be fully reversible with treatment. This highlights the importance of seeking out prompt medical care. 


Megaloblastic anemia is a blood condition in which you have large, underdeveloped red blood cells. Red blood cells carry oxygen to different areas of the body so that they can use it as energy. The lack of oxygen reaching your organs and tissue means that you may feel tired and depressed and experience muscle weakness.

Low folic acid or vitamin B12 levels can cause megaloblastic anemia. A doctor may recommend a blood test to establish what type of megaloblastic anemia you are experiencing. They may advise taking folic acid or vitamin B12 supplements to address your deficiency.

Most people recover with proper supplementation, but you should seek medical attention when you notice the gradual onset of symptoms to promote a full recovery. 

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Medical Reviewer: Angelica Balingit, MD
Last Review Date: 2022 Aug 19
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