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Vitamin B12 Deficiency Anemia - Forrest Health
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    Vitamin B12 Deficiency Anemia

    Topic Overview

    What is vitamin B12 deficiency anemia?

    Having vitamin B12 deficiency means that your body does not have enough of this vitamin. You need B12 to make red blood cells, which carry oxygen through your body. Not having enough B12 can lead to anemia, which means your body does not have enough red blood cells to do the job. This can make you feel weak and tired. Vitamin B12 deficiency can cause damage to your nerves and can affect memory and thinking.

    What causes vitamin B12 deficiency anemia?

    Most people get more than enough B12 from eating meat, eggs, milk, and cheese. Normally, the vitamin is absorbed by your digestive system—your stomach and intestines. 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.
    • You have had surgery to remove part of the stomach or the last part of your small intestine, called the ileum. This includes some types of surgery used to help very overweight people lose weight.
    • You have problems with the way your body digests food, such as sprue (also called celiac disease), Crohn's disease, bacteria growth in the small intestine, or a parasite.

    This anemia can also happen if you don't eat enough foods with B12, but this is rare. People who eat a vegan diet and older adults who don't eat a variety of foods may need to take a daily vitamin pill to get enough B12. Other causes include drinking alcohol and taking some prescription and nonprescription medicines.

    What is the recommended daily amount of vitamin B12?

    The amount of vitamin B12 you need depends on your age.

    Daily recommended B12:footnote 1

    Age (years)

    Daily amount of B12 (micrograms)


    0.9 mcg


    1.2 mcg


    1.8 mcg

    14 and older

    2.4 mcg

    Pregnant women

    2.6 mcg

    Breast–feeding women

    2.8 mcg

    What foods contain 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 folate, 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 2


    Serving size

    B12 amount (microgram)

    Beef liver

    3 ounces

    71 mcg


    3 ounces

    84 mcg

    Cereal fortified with 100% daily value for B12

    1 serving

    6 mcg

    Rainbow trout

    3 ounces

    3 mcg

    Nonfat plain yogurt

    8 ounces

    1 mcg

    Large egg

    1 egg

    ½ mcg

    Chicken breast

    ½ breast

    ½ 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 they 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 vitamin B12 deficiency anemia diagnosed?

    Your doctor will examine you and ask questions about your past health and how you are feeling now. You will also have blood tests to check the number of red blood cells and to see if your body has enough vitamin B12.

    The level of folic acid, another B vitamin, will be checked too. Some people whose vitamin B12 levels are too low also have low levels of folic acid. The two problems can cause similar symptoms. But they are treated differently.

    How is it treated?

    Vitamin B12 deficiency anemia is treated with supplements of vitamin B12. Taking supplements brings your level of vitamin B12 back to normal, so you do not have symptoms. To keep your level of vitamin B12 normal, you will probably need to take supplements for the rest of your life. If you stop taking them, you'll get anemia again.

    Your vitamin B12 supplements might be pills or shots. If you use shots, you can learn to give them to yourself at home. For many people, pills work just as well as shots. They also cost less and are easier to take. If you have been getting shots, ask your doctor if you can switch to pills. Another form of treatment is a vitamin B12 nasal spray (such as Nascobal).

    You can take steps at home to improve your health by eating a varied diet that includes meat, milk, cheese, and eggs, which are good sources of vitamin B12. Also, eat plenty of foods that contain folic acid, another type of B vitamin. These include leafy green vegetables, citrus fruits, and fortified breads and cereals.

    Can vitamin B12 deficiency anemia be prevented?

    Most people who eat animal products like 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 women who eat 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 shots or pills to prevent deficiency.



    1. Food and Nutrition Board, Institute of Medicine (2011). Dietary reference intakes (DRIs): Recommended dietary allowances and adequate intakes, vitamins. Available online:
    2. Office of Dietary Supplements, National Institutes of Health (2010). Dietary Supplement Fact Sheet: Vitamin B12. Available online:

    Other Works Consulted

    • Carmel R (2006). Cobalamin (Vitamin B12). In ME Shils et al., eds., Modern Nutrition in Health and Disease, 10th ed., pp. 482–497. Philadelphia: Lippincott Williams and Wilkins.
    • Food and Nutrition Board, Institute of Medicine (2011). Dietary reference intakes (DRIs): Recommended dietary allowances and adequate intakes, vitamins. Available online:
    • Gallagher ML (2012). Intake: The nutrients and their metabolism. In LK Mahan et al., eds., Krause's Food and the Nutrition Care Process, 13th ed., pp. 32–128. St. Louis: Saunders.
    • Green R (2010). Folate, cobalamin, and megaloblastic anemias. In K Kaushansky et al., eds., Williams Hematology, 8th ed., pp. 533–563. New York: McGraw-Hill.
    • Heimburger DC, et al. (2006). Clinical manifestations of nutrient deficiencies and toxicities: A resume. In ME Shils et al., eds., Modern Nutrition in Health and Disease, 10th ed., pp. 595–611. Philadelphia: Lippincott Williams and Wilkins.
    • Linker CA, Damon LE (2012). Blood disorders. In SJ McPhee, MA Papadakis, eds., 2012 Current Medical Diagnosis and Treatment, 51st ed., pp. 475–519. New York: McGraw-Hill.
    • Office of Dietary Supplements, National Institutes of Health (2010). Dietary Supplement Fact Sheet: Vitamin B12. Available online:


    Current as ofMay 6, 2018

    Author: Healthwise Staff
    Medical Review: E. Gregory Thompson, MD - Internal Medicine
    Martin J. Gabica, MD - Family Medicine
    Adam Husney, MD - Family Medicine

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