Vitamin B12, also called cobalamin, is a water-soluble vitamin. Water-soluble vitamins are stored in the body in limited amounts and are excreted through the urine. Therefore, it is a good idea to have them in your daily diet. Vitamin B12, the most complex of the vitamins, contains the metal cobalt in its structure.
Vitamin B12’s functions include the following:
|Age Group (in years)||
Recommended Dietary Allowance
Most diets provide adequate B12; deficiency is often a result of absorption problems. In the stomach's acidic environment and through the action of the enzyme pepsin, vitamin B12 is released from food. People who do not have enough stomach acid (such as those taking strong acid-neutralizing medications) may not be able to separate B12 from food. People with this problem, however, absorb B12 supplements without difficulty.
Two proteins are also important for the vitamin's absorption and transport: intrinsic factor (IF) and R proteins. A B12 deficiency can result if there are any problems with pepsin, IF, or R proteins. Reduced secretion may occur in mid- to late-life. Severely reduced levels of IF lead to a condition called pernicious anemia. People with pernicious anemia have trouble absorbing B12 supplements and may need either very high doses or injections.
Symptoms of vitamin B12 deficiency include the following:
Vitamin B12 has a low potential for toxicity. The tolerable upper intake level (UL) for vitamin B12 from dietary sources and supplements combined has not been determined. This does not mean that there is no potential for adverse effects resulting from high intakes. Because data is limited, caution should be used when supplementing.
No symptoms of vitamin B12 toxicity have been reported.
Vitamin B12 can be found in animal products, such as fish, meat, poultry, eggs, and milk. Some foods high in vitamin B12 include:
The following populations may be at risk for vitamin B12 deficiency and may require a supplement:
Megaloblastic anemia can occur as a result of either a folate deficiency or a vitamin B12 deficiency. Supplementing with folate can correct this anemia. But, it will not correct the B12 deficiency. Permanent nerve damage can result if a B12 deficiency is left untreated. If you have megaloblastic anemia, talk with your doctor about assessing your B12 status as well as your folate status.
Here are tips to help increase your intake of vitamin B12:
American Society for Nutrition
Eat Right—Academy of Nutrition and Dietetics
Centre for Science in the Public Interest
Vitamin B12. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated July 7, 2016. Accessed July 21, 2016.
Vitamin B12. Office of Dietary Supplements website. Available at: https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional. Updated February 11, 2016. Accessed July 21, 2016.
Vitamin B12. Oregon State Linus Pauling Institute website. Available at: http://lpi.oregonstate.edu/mic/vitamins/vitamin-B12. Updated June 4, 2015. Accessed July 21, 2016.
Vitamin B12 deficiency. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated December 4, 2015. Accessed July 21, 2016.
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Last reviewed July 2016 by Michael Woods, MD Last Updated: 7/21/2016