Vitamin B12, or cobalamin, is the only vitamin that contains an essential mineral, namely cobalt. This vitamin is not found at all in plants, and it is present in limited quantities in foods containing animal proteins. Cobalamin is one of the most difficult vitamins to acquire from your diet. Fortunately, humans only require small amounts. Vitamin B-12 has fewer functions than some other B vitamins, but those functions are critical. Unlike other B vitamins, B-12 is stored in your body.
Functions
Vitamin B-12 is involved in the synthesis of DNA in the chromosomes of nearly every cell in your body. Cobalamin is particularly vital for the formation and maintenance of normal nerve tissue. Without this nutrient, you would develop permanent damage to the white matter of your brain and spinal cord. Vitamin B-12 is also needed for the production of healthy red blood cells and the normal metabolism of fats, carbohydrates and proteins.
Sources
Vitamin B-12 is found in meat, fish, shellfish, eggs and milk products. Organ meats, such as liver and heart, contain more cobalamin than most other sources. Fermented soy products, such as tempeh and miso, contain small amounts. Because B-12 is not present in plant foods, strict vegans may develop B-12 deficiency unless they take supplements. Although bacteria in your gut make some cobalamin, the amount absorbed from this source is probably insufficient to meet your daily needs, according to Dr. Elson Haas, author of "Staying Healthy with Nutrition."
Absorption
Vitamin B-12 is unique in its absorption, too. When your stomach secretes hydrochloric acid, it also produces a protein called intrinsic factor, which is needed for optimal absorption of vitamin B-12. Intrinsic factor binds to B12 in the duodenum, just beyond your stomach, and the intrinsic factor B-12 complex is then absorbed in the lower end of your small intestine. If your stomach acid is decreased or if you have undergone surgery to remove part of your intestine, you may not absorb B-12 efficiently.
Storage
Your liver stores significant amounts of vitamin B-12. According to "The Merck Manual for Diagnosis and Therapy," liver stores can supply your needs for three to six years if you stop making intrinsic factor. If your small intestine is damaged or removed, however, you could develop deficiency within a few months. Your liver regularly releases vitamin B-12, and a specialized protein transports it through your bloodstream to the tissues where it is needed.
Pernicious Anemia
Although the term "pernicious anemia" is often used to describe all forms of vitamin B-12 deficiency, it is actually a specific condition that results from immune damage to the cells that make stomach acid and intrinsic factor. This often occurs in younger adults and is associated with a higher risk for stomach and intestinal cancers. A 2009 review in "American Family Physician" reports that infection with Helicobacter pylori, the bacterium responsible for most ulcers, can result in a pernicious anemia-like syndrome.
Daily Needs
Daily vitamin B-12 needs are measured in micrograms, rather than milligrams like most vitamins. Around 10 to 20 mcg is a reasonable daily dose, but people with higher protein intake, such as bodybuilders, may need larger amounts. Doses of 500 to 1,000 mcg or more are routinely used without any signs of toxicity. If you are found to be deficient in vitamin B-12, oral supplementation is sufficient for replenishing your B-12 stores. Sublingual forms that dissolve under your tongue are also available. Check with your physician to see if you need additional vitamin B-12.
References
- "Staying Healthy with Nutrition: Vitamin B12"; Elson M. Haas, M.D.; 2006
- "The Merck Manual of Diagnosis and Therapy, 18th Edition: Vitamin B12; Mark H. Beers, M.D., Editor-In-Chief; 2006
- "American Family Physician"; Evaluation of macrocytosis; Kaferle J, Strzoda C; 2009
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