Anemia Vitamin B12–Deficiency Anemia

What is vitamin B12–deficiency anemia?

What it is

Vitamin B12–deficiency anemia, also known as cobalamin deficiency, is a condition that develops when your body can't make enough healthy red blood cells because it doesn't have enough vitamin B12. Your body needs vitamin B12 to make healthy red blood cells , white blood cells , and platelets . Since your body doesn’t make vitamin B12, you have to get it from the foods you eat or from supplements.

You can get vitamin B12 deficiency if you can’t absorb vitamin B12 due to problems with your gut or if you have pernicious anemia, which makes it difficult to absorb vitamin B12 from your intestines. Without enough vitamin B12, blood cells do not form properly inside your bone marrow, the sponge-like tissue within your bones. These blood cells die sooner than normal, leading to anemia.

What are the symptoms of vitamin B12–deficiency anemia?


If you have vitamin B12–deficiency anemia, you may have the typical symptoms of anemia at first, such as fatigue, paleness, shortness of breath, headaches, or dizziness. If left untreated, you may start to notice brain and nervous system symptoms. This is because vitamin B12 is also needed for your brain and your nerves to work properly.

Your symptoms may include:

  • Tingling feelings or pain
  • Trouble walking
  • Uncontrollable muscle movements
  • Confusion, slower thinking, forgetfulness, and memory loss
  • Mood or mental changes, such as depression or irritability
  • Problems with smell or taste
  • Vision problems
  • Diarrhea and weight loss
  • Glossitis, which is a painful, smooth, red tongue

What causes vitamin B12–deficiency anemia?


You can develop vitamin B12–deficiency anemia if you do not eat enough food with vitamin B12, such as if you follow a strict vegetarian or vegan diet. But this is rare. In the United States, vitamin B12–deficiency anemia is most often due to other risk factors.

You can develop vitamin B12 deficiency for the following reasons:

  • Lack of intrinsic factor: Intrinsic factor is a protein made in the stomach, which helps the body absorb vitamin B12. People who have pernicious anemia do not produce intrinsic factor. Pernicious anemia is more common in people with northern European or African ancestry. You may develop vitamin B12–deficiency anemia if your body is not able to absorb enough vitamin B12 from the foods you eat. Older adults are more likely to have digestive problems that make it harder to absorb vitamin B12.
  • Lifestyle habits: Drinking too much alcohol can make it harder for your body to absorb vitamin B12. For men this is more than two drinks in a day. For women, it’s more than one drink in a day.
  • Medicines: Taking certain medicines can make it harder for your body to absorb vitamin B12 over time. These include some heartburn medicines and metformin to treat diabetes.
  • Medical conditions: Some medical conditions can raise your risk of vitamin B12–deficiency anemia. These include:
  • Stomach surgery: Surgery on your stomach or intestines, such as weight-loss surgery or gastrectomy, can make it harder for your body to absorb vitamin B12.

How do you prevent vitamin B12 deficiency?


If you are otherwise healthy, maintaining a normal diet enriched in vitamin B12 is important.

Foods that are good sources of vitamin B12 include:

  • Lean red meat and chicken
  • Fish, such as catfish and salmon; and seafood, such as clams and oysters
  • Milk, yogurt, cheese, and fortified vegan milk substitutes
  • Fortified cereals
  • Eggs

How much vitamin B12 do you need each day?

Vitamin B12 recommendations

The recommended daily amounts of vitamin B12 depend on your age, your sex, and whether you are pregnant or breastfeeding. Your healthcare provider can look at your medical history to help determine how much vitamin B12 you need each day.

Recommended daily vitamin B12 intake for children and adults

Recommended Daily Amounts of Vitamin B12, in micrograms (mcg)


Male or Female



1–3 years

0.9 mcg



4–8 years

1.2 mcg



9–13 years

1.8 mcg



14–18 years

2.4 mcg

2.6 mcg

2.8 mcg

19–50 years

2.4 mcg

2.6 mcg

2.8 mcg

51+ years

2.4 mcg (mostly from fortified foods or a supplement)



How is vitamin B12–deficiency anemia diagnosed?


To screen for vitamin B12–deficiency anemia, your healthcare provider may order blood tests to see whether you have low hemoglobin or vitamin B12 levels.

Healthy and Abnormal Blood Levels in Adults

Hemoglobin, g/dL



Men: 13 or higher

Women: 12 or higher



Men: 12 or lower

Women: 11 or lower

 Vitamin B12, pg/mL


400 or higher


Vitamin B12-deficiency

200 or lower (although levels may be normal in some cases)

Tests to screen for vitamin B12-deficiency anemia. A complete blood count measures hemoglobin. Another blood test measures vitamin B12 levels in the blood. You may still have the condition even if your vitamin B12 levels are normal.

How is vitamin B12–deficiency anemia treated?


If your doctor diagnoses you with vitamin B12–deficiency anemia, your treatment will depend on the cause and seriousness of your condition. Some people need lifelong treatment.

Different therapies can be used to treat anemia.

  • Vitamin B12 medicine can be prescribed by your provider for you to take by mouth or as a nose spray or a shot. These supplements can help increase the levels of vitamin B12 in your body. For serious vitamin B12–deficiency anemia, your doctor may recommend vitamin B12 shots until your levels are healthy.
  • Blood transfusions to treat serious vitamin B12–deficiency anemia in combination with vitamin B12 treatment.

Your care provider may also recommend you make some changes to your eating habits to help increase the amount of vitamin B12 in your diet.

Some symptoms may take months to improve, depending on how serious they are. Some symptoms related to the brain or the nerves, such as numbness and tingling, may not go away even with treatment.

What happens if vitamin B12–deficiency anemia is not treated?

What happens if not treated

Vitamin B12–deficiency may cause serious complications, such as bleeding, infections, and problems with your brain or nerves that may be permanent. Babies born to mothers who have vitamin B12–deficiency may have developmental delays and birth defects of the brain and spinal cord.

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