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Vitamin B12

Vitamin B12

Alternate Names

  • cobalamin
  • cyanocobalamin


Vitamin B12, also known by its chemical name, cobalamin, is a water-soluble vitamin. This means that it dissolves in water rather than in fat. Thus, any excess is excreted from the body, so excess amounts are not a problem. B-12 is one of the B-complex vitamins.

What food source is the nutrient found in?

Vitamin B12 is found in animal foods, fortified foods, and some fermented foods. Some sources of B12 are:
  • eggs
  • meat
  • poultry
  • fish
  • dairy products
  • tempeh and miso, which both come from soy
The amount of B12 in some foods includes:
  • salmon, cooked (3 oz) = 2.6 mcg (micrograms)
  • beef tenderloin lean, broiled (3 oz) = 2.2 mcg
  • milk (1 cup) = 0.5 mcg

How does the nutrient affect the body?

Vitamin B12 helps the body:
  • make red blood cells, with folic acid, another B-vitamin
  • work with many chemicals found in all body cells
  • copy the genetic code within each cell
  • form and maintain the nervous system
  • build and maintain protective coating around nerves
  • digest and use fats, carbohydrates, and some proteins for energy
  • form neurotransmitters in the brain, such as serotonin, that help regulate mood, sleep, and appetite


The recommended dietary allowance for adults, called RDA, for vitamin B12 is 2.4 micrograms (mcg) per day. For pregnant women, the RDA is 2.6 mcg; for nursing women, it is 2.8 mcg. A microgram is a very small amount. Since the only dietary sources of B12 are animal products, strict vegetarians may need to take supplements, or eat foods that have had the vitamin added.
Not getting enough vitamin B12 can cause:
  • anemia
  • fatigue
  • nerve damage, with symptoms such as tingling sensations and numbness
  • smooth tongue
  • very sensitive skin
  • muscle and nerve paralysis
Some people have trouble absorbing B12. Other people may just have poor dietary intake. Anemia can be treated with injections of B12. Strict vegetarians who eat no animal products, their infants, and older people are at the highest risk for vitamin B12 deficiency. For these people, eating fortified foods and/or taking dietary supplements can help prevent a deficiency. High intakes of folic acid can hide this type of anemia.
Getting too much vitamin B12 has no known symptoms or toxicity. Since it is water-soluble, any extra leaves the body in the urine. There is no proof that taking extra B12 boosts energy. Vitamins do not provide calories or create energy. Vitamins can help break down nutrients that yield energy. These nutrients include carbohydrate, protein, and fat.
Calcium is needed to help the body absorb vitamin B12. A deficiency of either iron or vitamin B6 can decrease the amount of B12 the body is able to absorb.


Somer, E., MA, RD.&Health Media of America. (1995). The Essential Guide To Vitamins and Minerals (2nd ed.). New York: HarperCollins Publishers, Inc. Duyff, R., MS, RD, CFCS. (1996). The American Dietetic Association's Complete Food&Nutrition Guide. Minnesota: Chronimed Publishing. Murray, M., ND. (1996). Encyclopedia of Nutritional Supplements. California: Prima Publishing.

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