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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:
- Assisting in the production of neurotransmitters, which are chemicals that regulate sleep, pain, and mood
- Enabling proper DNA replication
- Helping catalyze the reaction that produces succinyl-CoA, a chemical required for the synthesis of hemoglobin
- Making red blood cells and preventing anemia
|Age Group (in years)||
Recommended Dietary Allowance
Vitamin B12 Deficiency
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:
- Numbness and tingling of the arms or legs
- Difficulty walking
- Sore tongue
- Loss of appetite
- Memory loss
Vitamin B12 Toxicity
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.
Major Food Sources
Vitamin B12 can be found in animal products, such as fish, meat, poultry, eggs, and milk. Some foods high in vitamin B12 include:
- Beef liver
- Tuna fish
- Fortified breakfast cereals
Populations at Risk for Vitamin B12 Deficiency
The following populations may be at risk for vitamin B12 deficiency and may require a supplement:
- People with pernicious anemia—This condition occurs when there is an absence of intrinsic factor. A person who has pernicious anemia will need to be monitored by a physician and take lifelong supplemental vitamin B12.
- Older adults—The incidence of B12 deficiency among the elderly is high. A multivitamin may not contain enough B12 to compensate; talk with your healthcare provider about what your specific needs are for supplementation.
- People with gastrointestinal (GI) disorders—GI disorders, like celiac disease, Crohn's disease, or GI surgery, can lead to malabsorption of B12.
- Strict vegetarians—B12 is not present in any useful amounts in plant foods. Total vegetarians who consume no animal products may need to supplement with B12. Fortified cereal can be a good source of the vitamin for a vegetarian.
- People who consume excessive amounts of alcohol—Alcoholics tend to have diets lacking in several essential nutrients, including B12.
- People who take strong acid-neutralizing drugs—Those who take these medications cannot absorb B12 well from food and need to take supplements.
Folate Supplementation May Mask a B12 Deficiency
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.
Tips For Increasing Your Vitamin B12 Intake:
Here are tips to help increase your intake of vitamin B12:
- Rub a little olive oil, squeeze a bit of fresh lemon, and crack some black pepper and salt on a fresh piece of salmon. Grill on the barbecue or broil it in the oven.
- Have a bowl of fortified, high-fiber breakfast cereal in the morning.
- Mix canned tuna with some olive oil, white beans, and salt and pepper. Enjoy with some whole wheat crackers.
- For an afternoon snack, try a cup of yogurt. Jazz it up with some sliced fresh fruit or crunchy granola.
- Skewer large shrimp with mushrooms, tomatoes, onion, and zucchini. Brush on a marinade and toss on the barbecue.
- If you take a multivitamin/mineral supplement, make sure that it contains B12.
Academy of Nutrition and Dietetics
American Society for Nutrition
Centre for Science in the Public Interest
Andres E, Federici L, Affenberger S, et al. B12 deficiency: a look beyond pernicious anemia [review]. J Fam Pract. 2007;56:537-542.
Vitamin B12. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated July 5, 2013. Accessed October 14, 2014.
Vitamin B12. Office of Dietary Supplements website. Available at: http://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/. Updated June 24, 2011. Accessed October 14, 2014.
Vitamin B12. Oregon State Linus Pauling Institute website. Available at: http://lpi.oregonstate.edu/infocenter/vitamins/vitaminB12/. Updated January 2014. Accessed October 14, 2014.
Vitamin B12 deficiency. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed. Updated September 23, 2014. Accessed October 14, 2014.
Wierzbicki AS. Homocysteine and cardiovascular disease: a review of the evidence. Diab Vasc Dis Res. 2007;4:143-150.
3/6/2013 DynaMed's Systematic Literature Surveillance http://www.ebscohost.com/dynamed : Marti-Carvajal AJ, Lathyris D, Salanti G. Homocysteine lowering interventions for preventing cardiovascular events. Cochrane Database Syst Rev. 2013;1:CD006612.
- Reviewer: Michael Woods, MD
- Review Date: 09/2014
- Update Date: 10/14/2014