Vitamin B12, or cobalamin, is a water-soluble vitamin that the body requires daily to maintain health. Although it is water-soluble, which means that the body passes excess B12 in urine, your body can also store it. Vitamin B12 appears in meats, dairy products, fish and some plant foods.
Metabolism of Vitamin B12
Vitamin B12 cannot exist freely in its natural form; it appears bound to protein in foods. The synthetic form of vitamin B12, which may appear in supplements, can exist unbound. Once ingested, your stomach releases hydrochloric acid and intrinsic factor -- the acid breaks the protein bond, then the vitamin binds with the intrinsic factor. Once bound, B12 travels to the small intestine, where your body absorbs the B12 into the bloodstream and uses the vitamin throughout the body.
Uses in the Body
The body primarily uses vitamin B12 to maintain healthy blood and nerve cells. It also requires vitamin B12 to produce DNA, and the vitamin works alongside other B-complex vitamins to maintain a healthy metabolism. Deficiencies in vitamin B12 are rare, because although water-soluble, the body can store it in the liver for years. However, when they do occur, they can result in anemia, loss of balance, numbness and weakness.
Recommended Dosage
The recommended dosage of vitamin B12 varies by age. Everyone age 14 and older should have 2.4 mcg per day. Those ages 9 to 13 require 1.8 mcg, those 4 to 8 need 1.2 micrograms, those 1 to 3 should take in 0.9 mcg, and those 0 to 12 months require 0.4 to 0.5 mcg of vitamin B12 per day. There is no established upper limit for vitamin B12, though large doses may cause itching, rash, diarrhea, rosacea and hives.
Considerations
Vitamin B12 works best when consumed with a diet that includes all the B-complex vitamins. Although it may appear in plant foods, MedlinePlus.com states that the body insufficiently absorbs the nutrient from plants and that the best sources of the vitamin are meats, fish and seafood. Ten to 30 percent of adults over the age of 50 lose the ability to absorb vitamin B12 from foods due to a condition called atrophic gastritis and must take supplements. Supplemental forms of vitamin B12 include multivitamins, nasal gels, sublingual pills -- those that dissolve under the tongue -- and injections.
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