Like HowStuffWorks on Facebook!

How Vitamin B12 Works


What Is Vitamin B12
Vitamin B12, also called cyanocobalamin or cobalamin, is unique. It differs from other vitamins, even from others of the B complex, in many ways. It has a chemical structure much more complex than that of any other vitamin. It's the only vitamin to contain an inorganic element (the mineral cobalt) as an integral part of its makeup. And only microorganisms and bacteria can make vitamin B12 -- plants and animals can't.

The pursuit of vitamin B12 began in 1926, when two investigators found that patients who ate almost a pound of raw liver a day were effectively relieved of pernicious anemia. Scientists correctly speculated that liver contained a substance that prevents the disorder, but they wondered why victims of pernicious anemia needed it in such large quantities.

William Castle suggested that liver contained an anti-pernicious anemia (APA) factor. He also believed that people who had the disease lacked a factor intrinsically necessary to use the APA factor. By eating about a pound of liver a day, these people could counteract the lack of the intrinsic factor and absorb the APA factor they needed.

Oysters and other animal foods are good sources of vitamin B12.
© 2007 Publications International, Ltd.
Oysters and clams are surpassed only by liver as good sources of vitamin B12.

For the next 20 years, scientists searched for the APA factor. Progress was slow until 1948, when testing began on an experimental "animal" -- the microorganism Lactobacillus lactis. Instead of testing liver extracts on people, researchers tested them on the microorganisms. Since these microorganisms reproduce so quickly, many generations could be tested in a short period of time.

In less than a year, two research groups -- one in England and one in the United States -- both managed to isolate the APA factor -- pure vitamin B12.

Vitamin B12 is essential to cells because it's needed to assist folate in making DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), which carry and transmit genetic information for every living cell. This information tells a cell how to function and must be passed along each time a cell divides.

Rapidly dividing cells need a continuous supply of vitamin B12 and folate. Vitamin B12 plays a central role in folate metabolism. It releases free folate from its bound form so it can be absorbed, and it helps in the transportation and storage of folate.

A deficiency of vitamin B12 can create a folate deficiency even when dietary intake of folate is adequate. That is why a deficiency of either vitamin causes a similar type of anemia.

Vitamin B12 functions in the production of a material called myelin, which covers and protects nerve fibers. Without enough B12, the myelin sheath does not form properly or stay healthy. As a result, nerve transmission suffers, and people experience irreversible nerve damage.

It's a slow and insidious process that can ultimately end in death. Pernicious (anemia) in fact means, "leading to death."

Vitamin B12 is found mostly in animal foods, such as dairy products, eggs, liver, meat, clams, oysters, sardines, and salmon. Fermented bean products, such as tempeh, contain some vitamin B12. Manufacturers also add vitamin B12 to some cereal products.

Food Quantity Vitamin B12
Liver (beef) 3 1/2 ounces
70.4
Clams, canned 1/2 cup
24.7
Liver (chicken)
3 1/2 ounces
19.2
Oysters, raw 3 1/2 ounces
19
Sardines
3 1/2 ounces
8.7
Product 19 cereal 1 cup 6
Liverwurst 2 slices 4.8
Salmon, canned 3 1/2 ounces 4.3
Grape-Nuts cereal 1/2 cup 3
Hamburger 3 ounces 2.3
Tuna, canned in water 3 1/2 ounces 2.2
Lamb 3 1/2 ounces 2.1
Haddock 3 1/2 ounces
1.7
Beef steak 3 ounces 1.6
Veal, lean 3 1/2 ounces 1.4
Yogurt, low-fat 8 ounces 1.4
Flounder 3 1/2 ounces 1.2

Bacteria in the intestines make some vitamin B12, but far less than the amount needed daily.

B12 has shown promise against diseases from asthma to AIDS to Alzheimer's. Find out how it's used on the next page.

Vitamin B12 is just one of the many vitamins that are part of a healthy diet. Check out the following links to learn more:
  • Folate is necessary for healthy growth, because it makes DNA and RNA. Learn how it manufactures cells at How Folate Works.
  • When teamed with other B vitamins, B2 helps in metabolism. Find out what it does at How Vitamin B2 Works.
  • Relax; you'll find the stress-busting Vitamin B5 in every food you eat. Learn about it at How Vitamin B5 Works.
  • Your body can make its own Vitamin D if you get enough sunshine. Learn the details at How Vitamin D Works.
  • Vitamin E is an antioxidant, which keeps the blood clean. Separate truth from fiction at How Vitamin E Works.
  • To learn about the many vitamins in our diet, how much you should be eating, and where to find them, go to our general Vitamins page.
  • If you're looking for the best prices on B vitamins, click here.
This information is solely for informational purposes. IT IS NOT INTENDED TO PROVIDE MEDICAL ADVICE. Neither the Editors of Consumer Guide (R), Publications International, Ltd., the author nor publisher take responsibility for any possible consequences from any treatment, procedure, exercise, dietary modification, action or application of medication which results from reading or following the information contained in this information. The publication of this information does not constitute the practice of medicine, and this information does not replace the advice of your physician or other health care provider. Before undertaking any course of treatment, the reader must seek the advice of their physician or other health care provider.