Vitamin B12
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Vitamin B12

Definition

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.

Alternative Names

Cobalamin; Cyanocobalamin

Function

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

Food Sources

Vitamin B12 is found in:

  • Eggs
  • Fortified foods such as soymilk
  • Meat
  • Milk and milk products
  • Organ meats (liver and kidney)
  • Poultry
  • Shellfish

The body absorbs animal sources of vitamin B12 much better than plant sources. Non-animal sources of vitamin B12 vary in their amount of B12. They are not thought to be reliable sources of the vitamin.

Side Effects

A lack of vitamin B12 (B12 deficiency) occurs when the body does not get or is unable to absorb the amount of vitamin that the body needs.

  • Many people over age 50 lose the ability to absorb vitamin B12 from foods.
  • People who follow a strict vegetarian or vegan diet and do not consume eggs or dairy products may need vitamin B12 supplements.
  • Those who have had gastrointestinal surgery, such as weight loss surgery, lose the ability to absorb vitamin B12.
  • People who have digestive disorders, such as celiac disease or Crohn's disease, may not absorb enough vitamin B12.

Low levels of B12 can cause:

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

See also:

  • Megaloblastic anemia
  • Pernicious anemia

Recommendations

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

For people who do not eat animal products, vitamin B12 can be found in:

  • 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 form of vitamin B12 can be given by injection.
  • Another prescription form of vitamin B12 is a nasal gel (for use in the nose).
  • Vitamin B12 is also available in a form that dissolves under the tongue (sublingual), but the multivitamin pill form works as well.

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 breast-feeding need higher amounts. Ask your health care provider which amount is best for you.

Dietary Reference Intakes for vitamin B12:

Infants (adequate intake)

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

Children

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

Adolescents and Adults

  • Males and females age 14 and older: 2.4 mcg/day

References

Escott-Stump S, ed. Nutrition and Diagnosis-Related Care. 6th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2008.

Sarubin Fragaakis A, Thomson C. The Health Professional's Guide to Popular Dietary Supplements. 3rd ed. Chicago, Il: American Dietetic Association; 2007.

Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes: Thiamin, riboflavin, niacin, vitamin B6, folate, vitamin B12, pantothenic acid, biotin, and choline. Washington, DC: National Academy Press; 1998.



Review Date: 2/15/2011
Reviewed By: Alison Evert, MS, RD, CDE, Nutritionist, University of Washington Medical Center Diabetes Care Center, Seattle, Washington. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.
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