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Vitamin B12 Deficiency Anemia

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Vitamin B12 Deficiency Anemia

Condition Basics

What is vitamin B12 deficiency anemia?

Vitamin B12 deficiency anemia is a blood problem that occurs when your body doesn't have enough of this vitamin. Your body needs B12 to make red blood cells, which carry oxygen. Without enough B12, your body doesn't have enough red blood cells (anemia). Anemia can make you feel weak and tired.

What causes it?

Most people get more than enough B12 from eating meat, eggs, milk, and cheese. Vitamin B12 deficiency anemia usually happens when the digestive system is not able to absorb the vitamin. This can happen if you have:

  • Pernicious anemia. In this anemia, your body destroys the cells in your stomach that help you absorb vitamin B12.
  • Surgery to remove part of the stomach or the last part of your small intestine (ileum). This includes some types of weight-loss surgery.
  • Problems with the way your body digests food, such as sprue (celiac disease) or Crohn's disease.

This anemia can also occur in people who don't eat enough foods with B12. This may include people who eat a vegan diet and older adults who don't eat a variety of foods.

Other causes include drinking alcohol and taking certain medicines.

Recommended amounts of vitamin B12

The amount of vitamin B12 you need each day depends on your age and situation.footnote 1

  • Age 1 to 3 years: 0.9 micrograms (mcg) a day
  • Age 4 to 8 years: 1.2 mcg
  • Age 9 to 13 years: 1.8 mcg
  • Age 14 and older: 2.4 mcg
  • During pregnancy: 2.6 mcg
  • While breastfeeding: 2.8 mcg

What are the symptoms?

If your vitamin B12 deficiency is mild, you may not have symptoms or you may not notice them. Some people may think the symptoms are just the result of growing older. As the anemia gets worse, you may:

  • Feel weak, tired, and lightheaded.
  • Have pale skin.
  • Have a sore, red tongue or bleeding gums.
  • Feel sick to your stomach and lose weight.
  • Have diarrhea or constipation.

If the level of vitamin B12 stays low for a long time, it can damage your nerve cells. If this happens, you may have:

  • Numbness or tingling in your fingers and toes.
  • A poor sense of balance.
  • Depression.
  • A decrease in mental abilities.

How is it diagnosed?

Your doctor will ask about your symptoms and past health and will do a physical exam. You'll have blood tests to check the number of red blood cells and the levels of vitamin B12 and folate. Some people with low B12 also have low folate. These problems cause similar symptoms but have different treatments.

How is vitamin B12 deficiency anemia treated?

To treat this anemia, your doctor will prescribe vitamin B12 supplements. These might be pills or shots. Taking the supplements brings your level of B12 back to normal. To keep your level normal and prevent anemia, you will probably need to take the supplements for the rest of your life.

How can you prevent it?

Most people who eat animal products like meat, milk, cheese, and eggs will not get this B12 deficiency anemia. People who follow a vegan diet can prevent it by taking a daily vitamin pill or by eating foods that have been fortified with B12.

Babies born to someone who eats a vegan diet should be checked by a doctor to see whether they need extra vitamin B12.

If you have pernicious anemia or another reason you cannot absorb enough vitamin B12, your doctor will give you vitamin B12 to prevent deficiency. This may be through shots, pills, or a nasal spray.

Foods that contain vitamin B12

Vitamin B12 is found in foods from animals, such as meat, seafood, milk products, poultry, and eggs. It is not in foods from plants unless it has been added to the food (fortified). Some foods, like cereals, are fortified with vitamin B12.

Supplements containing only B12, or B12 along with other B vitamins and/or folic acid, are readily available. Also, B12 is usually in multivitamins. Check the label to find out how much B12 is in a supplement.

Estimates of B12 in certain foodsfootnote 1


Serving size

B12 amount (micrograms)


3 ounces

17 mcg


3 ounces

2.6 mcg

Cereal fortified with 100% daily value for B12

1 serving

2.4 mcg

Nonfat plain yogurt

6 ounces

1 mcg

Large egg

1 egg

0.5 mcg

Turkey breast, roasted

3 ounces

0.3 mcg


½ cup

0.1 mcg



  1. Office of Dietary Supplements (2022). Vitamin B12 fact sheet for health professionals. National Institutes of Health. Accessed February 14, 2023.


Current as of: December 13, 2023

Author: Healthwise Staff
Clinical Review Board
All Healthwise education is reviewed by a team that includes physicians, nurses, advanced practitioners, registered dieticians, and other healthcare professionals.

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