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Alternative Names Return to topCobalamin; Deficiency - B12
Definition Return to top
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.
Typically, water-soluble vitamins can not be stored by the body. Vitamin B12 is special, because the body can store it for years in the liver.
Function Return to top
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 Return to top
Vitamin B12 is found in eggs, meat, poultry, shellfish, milk, and milk products.
Side Effects Return to top
Vitamin B12 deficiencies occur when the body is unable to properly use the vitamin. Pernicious anemia can make the body unable to absorb vitamin B12 from the intestinal tract.
Because vitamin B12 comes primarily from animal products, people who follow a strict vegetarian or vegan diet and do not consume eggs or dairy products may require vitamin B12 supplements. (Non-animal sources of vitamin B12 exist but are highly variable in their B12 content. They are considered unreliable sources of the vitamin.)
Those who had surgery on specific parts of the small intestine or stomach are also prone to a deficiency if they do not take B12 supplements.
Low levels of B12 can cause anemia, numbness or tingling in the arms and legs, weakness, and loss of balance.
Recommendations Return to top
The Food and Nutrition Board at the Institute of Medicine recommends the following dietary intake for vitamin B 12:
Adolescents and Adults
Specific recommendations depend on age, gender, and other factors (such as pregnancy). Women who are pregnant or producing breast milk (lactating) need higher amounts. Ask your health care provider which amount is best for you.
The best way to get the daily requirement of essential vitamins is to eat a balanced diet that contains a variety of foods from the food guide pyramid.
References Return to top
Rakel D, ed. Integrative Medicine. 2nd ed. Philadelphia, Pa: Saunders Elsevier; 2007.
Hamrick I, Counts SH. Vitamin and mineral supplements. Wellness and Prevention. December 2008:35(4);729-747.
Mason JB. Vitamins, trace minerals, and other micronutrients. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 237.
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.Update Date: 3/14/2009 Updated by: Linda Vorvick, MD, Family Physician, Seattle Site Coordinator, Lecturer, Pathophysiology, MEDEX Northwest Division of Physician Assistant Studies, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.