Vitamin B12 functions to help keep nerves healthy, support the production of red blood cells and induces the body to make substances necessary for the production of healthy genetic material, also known as DNA. Most Americans get enough vitamin B12 in their diet, according to the National Institutes of Health's Office of Dietary Supplements (ODS), and because the body absorbs it easily and can store it, deficiency rarely occurs. Some conditions, such as pernicious anemia, a condition that destroys the parietal cells in the stomach, interfere with the absorption of vitamin B12, resulting in a deficiency. Those with a B12 deficiency can increase their level through reliable sources.
Natural Foods
Many animal products naturally contain vitamin B12. These include fish, poultry and beef, with beef liver containing the most vitamin B12 per serving. Milk, produced by the mammary glands of some animals, also contains vitamin B12. Dairy products, defined by the U.S. Department of Agriculture as products produced from milk that retain their calcium content, also serve as a good natural source of vitamin B12. Although raw eggs provide slightly more vitamin B12 than cooked eggs, all eggs contribute to the daily vitamin B12 intake.
Fortified Foods
Since all natural sources of vitamin B12 come from animals, vegetarians and especially vegans -- those who refrain from consuming any animal products -- must get their daily recommended allowance in other types of foods. Food manufacturers therefore add vitamin B12 to some foods, creating fortified foods. Many breakfast cereals contain 100 percent of the daily allowance of B12, according to the ODS. Other foods fortified with vitamin B12 include yeast extracts, vegetable stocks, textured vegetable proteins and soya milks.
Supplements
Vitamin B12 supplements deliver forms of the vitamin readily absorbed by the body. In natural sources, vitamin B12 binds to the protein. When ingested, the hydrochloric acid and proteases in the stomach break these bonds and the free vitamin B12 binds to intrinsic factor -- a protein produced by the parietal cells in the stomach -- and travels to the small intestine for absorption. Vitamin B12 ingested in supplements or fortified foods does not require the initial separation step, but it still depends upon intrinsic factor for absorption.
Prescription Medications
Vitamin B12 is also available as a prescription medication usually delivered as an intramuscular injection. Doctors prescribe this type of B12 supplementation to treat extreme B12 deficiencies often caused by pernicious anemia or other conditions that interfere with the absorption of nutrients. A newer prescription formulation, a gel applied intranasally, may also effectively increase levels of B12 in the blood but still requires additional testing, according to the ODS.
