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Vitamin B12

Cobalamin; Cyanocobalamin

Vitamin B12 is a water-soluble vitamin. Water-soluble vitamins dissolve in water. After the body uses these vitamins, leftover amounts leave the body through the urine.

The body can store vitamin B12 for years in the liver.

Function

Vitamin B12, like the other B vitamins, is important for protein metabolism. It helps in the formation of red blood cells and in the maintenance of the central nervous system.

Food Sources

Vitamin B12 is naturally found in animal foods such as fish, meat, poultry, eggs, milk, and milk products. Vitamin B12 is generally not present in plant foods. Fortified breakfast cereals are a readily available source of vitamin B12. The vitamin is more available to the body from these cereals for vegetarians. Some nutritional yeast products also contain vitamin B12.

You can get the recommended amounts of vitamin B12 by eating a variety of the foods including:

  • Organ meats (beef liver)
  • Shellfish (clams)
  • Meat, poultry, eggs, milk and other dairy foods
  • Some fortified breakfast cereals and nutritional yeasts

To find out if vitamin B12 has been added to a food product, check the nutrition fact panel on the food label.

The body absorbs vitamin B12 from animal sources much better than plant sources. Non-animal sources of vitamin B12 have different amount of B12. They are not thought to be good sources of the vitamin.

Side Effects

Vitamin B12 deficiency occurs when the body does not get or is not able to absorb the amount of vitamin that the body needs.

Deficiency occurs in people who:

  • Are over the age of 50
  • Follow vegetarian or vegan diet
  • Have had stomach or intestinal surgery, such as weight loss surgery
  • Have digestive conditions such as celiac disease or Crohn disease

Talk to your health care provider about taking Vitamin B12 supplements.

Low levels of B12 can cause:

  • Anemia
  • Pernicious anemia
  • Loss of balance
  • Numbness or tingling in the arms and legs
  • Weakness

Recommendations

The best way to meet your body's vitamin B12 needs is to eat a wide variety of animal products.

Supplemental vitamin B12 can be found in the following:

  • Almost all multivitamins. Vitamin B12 is better absorbed by the body when it is taken along with other B vitamins, such as niacin, riboflavin, vitamin B6, and magnesium.
  • A prescription form of vitamin B12 can be given by injection or as a nasal gel.
  • Vitamin B12 is also available in a form that dissolves under the tongue (sublingual).

The Recommended Dietary Allowance (RDA) for vitamins reflects how much of each vitamin most people should receive on a daily basis. The RDA for vitamins may be used as goals for each person.

How much of each vitamin you need depends on your age and gender. Other factors, such as pregnancy and illnesses, are also important. Women who are pregnant or breastfeeding need higher amounts. Ask your provider which amount is best for you.

Dietary Reference Intakes for vitamin B12:

Infants (adequate intake)

  • 0 to 6 months: 0.4 micrograms per day (mcg/day)
  • 7 to 12 months: 0.5 mcg/day

Children

  • 1 to 3 years: 0.9 mcg/day
  • 4 to 8 years: 1.2 mcg/day
  • 9 to 13 years: 1.8 mcg/day

Adolescents and Adults

  • Males and females age 14 and older: 2.4 mcg/day
  • Pregnant teens and women: 2.6 mcg/day
  • Breastfeeding teens and women: 2.8 mcg/day

References

Mason JB. Vitamins, trace minerals, and other micronutrients. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 218.

Salwen MJ. Vitamins and trace elements. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 23rd ed. St Louis, MO: Elsevier; 2017:chap 26.

Text only

  • Vitamin B12 benefits - illustration

    Vitamin B12 is important for metabolism. Metabolism within the body includes the processes of energy generation and use; including nutrition, digestion, absorption, elimination, respiration, circulation, and temperature regulation.

    Vitamin B12 benefits

    illustration

  • Vitamin B12 source - illustration

    The human body stores several years' worth of vitamin B12, so nutritional deficiency of this vitamin is extremely rare. Although, people who follow a strict vegetarian diet and do not consume eggs or dairy products may require vitamin B12 supplements.

    Vitamin B12 source

    illustration

  • Vitamin B12 benefits - illustration

    Vitamin B12 is important for metabolism. Metabolism within the body includes the processes of energy generation and use; including nutrition, digestion, absorption, elimination, respiration, circulation, and temperature regulation.

    Vitamin B12 benefits

    illustration

  • Vitamin B12 source - illustration

    The human body stores several years' worth of vitamin B12, so nutritional deficiency of this vitamin is extremely rare. Although, people who follow a strict vegetarian diet and do not consume eggs or dairy products may require vitamin B12 supplements.

    Vitamin B12 source

    illustration

Tests for Vitamin B12

 

 

Review Date: 2/2/2019

Reviewed By: Emily Wax, RD, CNSC, University of Virginia Health System, Charlottesville, VA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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