Megaloblastic Anemia


What is megaloblastic anemia?

Megaloblastic anemia is a form of macrocytic anemia. Macrocytic anemia is a blood disorder that causes your bone marrow to make abnormally large red blood cells. It’s also a type of vitamin deficiency anemia. This condition happens when you don’t get enough vitamin B12 and/or vitamin B9 (folate). Healthcare providers treat megaloblastic anemia with vitamin B12 and vitamin B9 supplements.

How does megaloblastic anemia affect my body?

Your body needs a certain amount of healthy red blood cells to carry oxygen from your lungs to your tissues and back again. Like all blood cells, red blood cells start as stem cells in your bone marrow. Vitamin B12 and vitamin B9 help form red blood cells. Without enough vitamin B12 or vitamin B9, your body produces abnormal cells called megaloblasts.

Megaloblasts don’t divide and reproduce like healthy cells, which means there are fewer red blood cells in your bone marrow. The abnormal cells are unusually large, so large they often can’t get out of your bone marrow to move into your bloodstream. And even if they do make their way into your bloodstream, the abnormal cells die earlier than healthy red blood cells. Combined, these factors reduce the number of red blood cells, causing anemia.

Is megaloblastic anemia a serious illness?

Megaloblastic anemia is caused in part by vitamin B12 deficiency. Left untreated, vitamin B12 deficiency can cause neurological issues, including memory loss, problems with balance and paresthesia, which is a sense of tingling or prickling in your arms and legs.

How common is megaloblastic anemia?

Megaloblastic anemia isn’t rare. Healthcare providers don’t have enough information to say exactly how many people may have megaloblastic anemia.

Symptoms and Causes

What causes megaloblastic anemia?

Megaloblastic anemia happens when you don’t have enough vitamin B12 or vitamin B9 to make sure your bone marrow develops enough healthy red blood cells to carry oxygen throughout your body.

What causes vitamin B12 deficiency?

Some people develop vitamin B12 deficiency because their diet doesn’t include enough vitamin B12-rich foods like meat, fish, eggs and dairy products. Some people develop vitamin B12 deficiency because they have conditions or have had medical treatments that affect their ability to absorb vitamin B12. Those conditions include

  • Pernicious anemia: This autoimmune disorder keeps your body from absorbing vitamin B12.
  • Gastrectomy: This surgery removes part of your stomach, which may affect vitamin B12 absorption.
  • Zollinger-Ellison syndrome: This rare condition keeps your body from absorbing vitamin B12.
  • Blind loop syndrome: Blind loop syndrome happens when food you’ve digested stops moving through your intestines, causing bacteria overgrowth that uses up vitamin B12.
  • Fish tapeworm infestation: You can get a tapeworm infection or infestation by eating infected fish that was undercooked. Tapeworms feed on vitamin B12.
  • Pancreatic insufficiency: This condition affects your pancreas’ ability to make enough digestive enzymes to break down food, which means you may not get all the nutrients you need, including enough vitamin B12 or vitamin B9.

What causes vitamin B9 (folate) deficiency?

People may develop vitamin B9 (folate) deficiency if their daily diet doesn’t include green vegetables, fruits, meat and liver or foods that are enriched with folic acid. Other causes may include:

  • Digestive system diseases: Your digestive system doesn’t absorb folic acid well if you have a disease such as Crohn’s disease or celiac disease.
  • Excessive alcohol use: People who drink large amounts of alcohol sometimes substitute alcohol for food. As a result, they don’t get enough folate.
  • Overcooking your fruits and vegetables: When you overcook produce, the heat can destroy naturally occurring folate.
  • Hemolytic anemia: A blood disorder that occurs when your red blood cells are broken down and your bone marrow can’t replace red blood cells fast enough.
  • Certain medications: Some antiseizure drugs and ulcerative colitis drugs interfere with the proper absorption of folate.
  • Dialysis: Sometimes, people receiving dialysis for kidney failure have poor appetites, which affects how much vitamin B12 they receive from food.

What are the signs and symptoms of megaloblastic anemia?

Megaloblastic anemia symptoms are similar to symptoms of other types of anemia:

  • Fatigue: This is feeling too tired to complete daily activities.
  • Weakness: You may feel as if you don’t have enough muscle strength to get around easily or manage daily activities.
  • Pallor: Your skin is more pale than usual.
  • Shortness of breath (dyspnea): You may feel as if you can’t catch your breath or take a deep breath.
  • Feeling light-headed or woozy: Feeling as if you may faint.

Vitamin B12 deficiency sometimes affects your nerves, causing symptoms like tingling sensations, loss of sensation or muscle weakness.

Diagnosis and Tests

How do healthcare providers diagnose megaloblastic anemia?

Healthcare providers diagnose megaloblastic anemia by doing a physical examination and asking questions about your symptoms. They may do the following blood tests:

  • Complete blood count (CBC): Healthcare providers use this test to evaluate your red blood cell count and function.
  • Peripheral blood smear (PBS): This test is a technique healthcare providers use to examine your blood cells. Unlike some blood tests analyzed by a machine, healthcare providers perform the analysis by looking at blood cells under a microscope.
  • Reticulocyte count: A reticulocyte count measures the number of immature red blood cells (reticulocytes) in your bone marrow. Healthcare providers measure reticulocytes to find out if your bone marrow is producing enough healthy red blood cells.

Management and Treatment

How do healthcare providers treat megaloblastic anemia?

Providers treat megaloblastic anemia with vitamin supplements. Here’s more information:

  • Vitamin B12 deficiency treatment: Your healthcare provider may recommend you receive vitamin B12 injections for several weeks as your vitamin B12 levels return to normal. If you have vitamin B12 deficiency because your body can’t absorb vitamin B, you may need B12 injections every few months for the rest of your life. Likewise, people who have vitamin B12 anemia (pernicious anemia) may need to take vitamin B12 supplements for the rest of their lives.
  • Vitamin B9 deficiency treatment: Your healthcare provider may also prescribe folic acid tablets to solve vitamin B9 deficiency. They may check your vitamin B12 levels to make sure they’re normal. Sometimes, vitamin B9 supplements improve megaloblastic anemia symptoms, hiding an underlying vitamin B12 deficiency that could lead to neurological problems.
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How can I reduce my risk of developing megaloblastic anemia?

There are several ways to reduce your risk:

  • Try to eat a balanced diet that emphasizes foods containing vitamin B12 and vitamin B9.
  • Drink alcohol in moderation. Regular alcohol consumption may affect your digestive system and keep your body from absorbing vitamin B12.
  • If you have a condition that keeps your body from absorbing these vitamins, work with your healthcare provider to manage your condition.

Foods with vitamin B12

  • Animal food products: Red meat, fish, poultry, eggs, milk and other dairy products all contain vitamin B12.
  • Fortified foods: Fortified foods are foods that have certain vitamins and nutrients added to them that they don’t naturally have. Fortified foods include certain breakfast cereals, nutritional yeast, plant milk and certain bread. Be sure to check the food label (nutritional facts) to confirm the food is fortified with vitamin B12.

Foods with vitamin B9

  • Vegetables: Dark green leafy vegetables, peas, beans and legumes.
  • Fruits: Citrus fruits.
  • Animal food products: Liver, seafood, meat and poultry.
  • Eggs and dairy.
  • Fortified foods: Certain breads, flour, pasta, rice and cereal contain folic acid. Be sure to check the food label (nutritional facts) to confirm the food is fortified with vitamin B9.

Outlook / Prognosis

What can I expect if I have megaloblastic anemia?

Most people recover from megaloblastic anemia after receiving vitamin supplements. Your healthcare provider will monitor your vitamin levels periodically to confirm you’re getting enough vitamin B12 and vitamin B9. For example, they may schedule blood tests a few weeks after you start treatment to confirm the supplements are increasing your vitamin B12 and/or B9 levels.

Living With

How do I take care of myself?

Take care of yourself by:

  • Taking the vitamin supplements your healthcare provider prescribed.
  • Developing healthy eating habits that ensure you’re getting enough vitamin B12 and vitamin B9.
  • Monitoring your health and following up with your healthcare provider if you notice your anemia symptoms come back.

A note from Cleveland Clinic

If you have megaloblastic anemia, it means you’re not getting enough vitamin B12 and/or vitamin B9. These vitamins help your body make healthy red blood cells. Healthy red blood cells do essential work. They carry oxygen throughout your body. Fortunately, healthcare providers can treat this vitamin deficiency with supplements to boost your vitamin B12 and vitamin B9 levels. You can support supplements by eating a vitamin-rich diet. Ask your healthcare provider about ways you can make sure you’re getting enough vitamin B12 and vitamin B9. They’ll be glad to help.

Last reviewed by a Cleveland Clinic medical professional on 05/27/2022.


  • Hariz A, Bhattacharya PT. Megaloblastic Anemia. ( [Updated 2021 Oct 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Accessed 5/27/2022.
  • Merck Manuals. Vitamin Deficiency Anemia. ( Accessed 5/27/2022.
  • National Health Service. Vitamin B12 or Folate Deficiency Anemia – Treatment. ( Accessed 5/27/2022.
  • Socha D, DeSouza S, Flagg A, Sekeres M, Rogers H. Severe Megaloblastic Anemia: Vitamin Deficiency And Other Causes. Cl J. Med.Mar 2020, 87 (3) 153-164; Accessed 5/27/2022.

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