Health Library

Health Library Explorer
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A-Z Listings
Click 'Back to Intro' to return to the beginning of this section.

Vitamin B-12

Other name(s):

cobalamin, cyanocobalamin, hydroxocobalamin

General description

Vitamin B-12 is a water-soluble vitamin. That means it can dissolve in water. B-12 is needed for red blood cells to form brain and nerve function. It is also needed for making DNA. It’s found only in animal-based foods. B-12 helps your body make energy like the other B vitamins.

Vitamin B-12 is closely linked with folic acid (vitamin B-9). Vitamin B-12 and folic acid are needed to make purines and pyrimidines in your body. These are the building blocks of DNA.

Vitamin B-12 deficiency, like folic acid deficiency, causes megaloblastic anemia. This is when you have abnormally large red blood cells and immature, abnormal white cells. This is also called pernicious anemia. It occurs when the body is unable to absorb dietary vitamin B-12. This is due to not having enough of a protein (intrinsic factor) in the stomach. This issue is often hereditary.

Vitamin B-12 also helps turn homocysteine into methionine in your body. These are types of amino acids. This keeps homocysteine from building up. A high level of homocysteine increases the risk of certain cardiovascular diseases.. Vitamin B-12 keeps the protective cover called the myelin sheath around your nerves. Not having enough B-12 can cause nerve damage (neuropathy). This causes numbness and abnormal feelings in your skin.

Vitamin B-12 is also a factor in how carbohydrates are used in your body.

Medically valid uses

Vitamin B-12 is used to treat pernicious anemia caused by lack of an intrinsic factor. Supplements are also used for low levels of vitamin B-12. This can happen from any of these:

  • A vegan diet

  • Poor eating habits

  • Toxicity due to an overactive thyroid gland (thyrotoxicosis)

  • Excess bleeding

  • Cancer

  • Liver or kidney disease

  • Having a fish tapeworm (Diphyllobothrium latum)

Vitamin B-12 is used to treat some inherited or genetic issues that affect metabolic functions. These include:

  • Imerslund-Gräsbeck syndrome

  • Homocystinuria

  • Cobalamin C, D, and F disease

Unsubstantiated claims

There may be benefits that have not been proven through studies.

Vitamin B-12 may increase energy and give you a sense of well-being. It may also help your immune system work well. It may also improve your memory and boost fertility.

Recommended intake

Vitamin B-12 is measured in micrograms (mcg). It’s available as an oral tablet. It comes in strengths of 25 to 250 mcg. It’s also available as a nasal gel or sublingual pills. Sublingual means under the tongue. It can also be given by injection. Your body can't absorb all the vitamin B-12 from dietary supplements. Absorption is limited by how much intrinsic factor your stomach makes. Intrinsic factor is needed for your body to absorb B-12. For example, only about 10 mcg of a 500mcg oral supplement is actually absorbed in healthy people.

The RDA is the recommended dietary allowance.



Infants (0–6 months)

0.4 mcg

Infants (6 months to 1 year)

0.5 mcg

Children (1–3 years)

0.9 mcg

Children (4–8 years)

1.2 mcg

Children (9-13 years)

1.8 mcg

Children and adults (14 years and older)

2.4 mcg

Pregnant women

2.6 mcg

Breastfeeding women

2.8 mcg

Food source

Vitamin B-12 content

Liver, beef, cooked, 3 ounces

70.7 mcg

Clams cooked (without shells), 3 ounces

17 mcg

Salmon, cooked, 3 ounces

2.6 mcg

Tuna, light, canned in water, 3 ounces

2.5 mcg

Beef, ground, 3 ounces

2.4 mcg

Milk, 2% milkfat, 1 cup

1.3 mcg

Cheddar cheese, 1 ½ ounces

0.5 mcg

Vitamin B-12 isn’t found in vegetables or fruits. It is found in animal products. These include fish, meat, poultry, eggs, milk, and milk products. It is added to breakfast cereals. They are called fortified breakfast cereals. Some nutritional yeast products also contain vitamin B-12. Fortified foods vary in how much B-12 they have. The product labels tell you how much the product contains.

Bacteria in the large intestine may be able to create some vitamin B-12. But the amount can vary. And it's not known whether it's excreted with stool or absorbed back into the body. Normally, the small intestine is where B-12 is absorbed in the gut. If it can't absorb B-12, it is not used by the body and is lost through stool.

Vitamin B-12 is stable at room temperature. It doesn’t need to be refrigerated. Cooking doesn’t destroy it. Vitamin B-12 doesn't break down for several hours. This is so even at the boiling point of water.

A diet low in animal proteins, milk, or dairy foods may increase the need for vitamin B-12. People who eat vegan diets may need to take B-12 supplements. Breastfed babies of vegans also need supplements.

You may need supplements if you have a condition that causes you not to absorb enough B-12. These can include:

  • Gluten-induced enteropathy

  • Celiac disease

  • Sprue

  • Having a fish tapeworm

  • Weight loss surgery or surgery to remove all or part of the stomach (gastrectomy)

  • Heavy alcohol use

  • Liver disease

  • Hypothyroidism

  • Thalassemia

Vitamin B-12 absorption in the intestinal tract may decrease with age. So, people over age 60 may need vitamin B-12 supplements.

Women who are pregnant or breastfeeding may need to take B-12 supplements. Always talk with your healthcare provider before doing so.

Vitamin B-12 deficiencies tend to be caused by not getting enough B-12 in your diet. They can also be due to a reduced secretion or lack of intrinsic factor. This is a stomach secretion that helps the body absorb vitamin B-12.

Pernicious anemia is a rare blood disorder. This is where the body can't correctly use vitamin B-12. Vitamin B-12 is needed for the development of red blood cells. It's thought to be an autoimmune disorder. It may be hereditary because it tends to run in families.

Symptoms of pernicious anemia can include:

  • Weakness, severe tiredness (fatigue), or a sudden spinning feeling (vertigo)

  • Feeling lightheaded

  • Shortness of breath

  • Chest pain

  • Ringing in your ears (tinnitus)

  • Fast heart rate (tachycardia)

  • Yellowish color to the skin (jaundice)

  • Sore tongue or a smooth, "beefy" red tongue

  • Loss of appetite with weight loss

  • Diarrhea

  • Numbness, tingling, abnormal feelings, or sensitivity in your hands or feet

  • Muscle weakness

  • Unstable walking

  • Irritability, memory loss, dementia, and psychosis

Side effects, toxicity, and interactions

There are no known side effects of B-12. There are also no known food interactions linked with it.

Some medicines may decrease vitamin B-12 absorption from food. These include proton pump inhibitors, metformin, and histamine H2 receptor antagonists. Talk with your healthcare provider about your vitamin B-12 status if you take any of these medicines on a prolonged basis.

You shouldn’t take vitamin B-12 if you’re sensitive to it or cobalt. Allergic reactions can happen with the injectable form of B-12 in rare cases.

Additional information

Vitamin B-12 is absorbed in the lower part of the small intestine. It’s highly bound to plasma proteins in the bloodstream. These are called transcobalamins. The half-life is about 6 days.

Online Medical Reviewer: Anne Fetterman RN BSN
Online Medical Reviewer: Bianca Garilli MD
Online Medical Reviewer: Jessica Gotwals RN BSN MPH
Date Last Reviewed: 8/1/2023
Contact Our Health Professionals
Follow Us