Vitamin B12, also called cobalamin, is an essential nutrient required for the production of blood cells and normal function of the nervous system and intestinal tract. A lack of B12 causes anemia, which is a deficiency of red blood cells that carry oxygen. It can also cause nerve damage in the brain and spinal cord. B12 deficiency is usually caused by conditions that prevent its absorption by the small intestine. It less commonly results from inadequate dietary intake, for example in strict vegetarians. There are several ways to replace the missing vitamin.
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There are three different forms of B12 which differ slightly in chemical structure. Cyanocobalamin is the most widely used form in the United States. Methylcobalamin and hydroxycobalamin are both available as nutritional supplements but are rarely used. There is no evidence that one particular type of B12 is more effective, according to the journal "Haematologica."
The initial goals of treatment are to correct anemia, replace the body’s B12 stores, and prevent damage to the nervous system. A delay in treatment can result in irreversible nerve damage. After B12 levels in the blood and body return to normal, treatment is frequently continued to prevent recurrent deficiency.
B12 deficiency is usually treated with vitamin shots or pills. B12 injections are given in a muscle or under the skin which circumvents intestinal absorption. Vitamin B12 pills are effective in most people with poor absorption. Since 1 to 2 percent of each dose is absorbed, high doses provide an adequate amount of B12.
B12 is also available as a sublingual tablet placed under the tongue, a lozenge and a liquid spray for the mouth. A nasal spray is another alternative for people who have trouble swallowing pills. A study published in the journal "Gastroenterology" in 1997 showed that B12 is well-absorbed when used in nasal spray form with a rapid eight-fold increase in the vitamin level.
The dose and frequency of B12 depend on both the method of replacement and cause of the deficiency. A 50 mcg supplement will correct a nutritional deficiency. The dose for people with impaired absorption is 400 to 500 times higher than the recommended dietary allowance or RDA of 2.4 mcg a day. A tablet containing 1,000 to 2,000 mcg of B12 is usually sufficient. A study in the journal "Blood" published in 1998 showed that a 2,000 mcg pill taken daily was as effective as B12 shots.
B12 shots typically contain 1,000 mcg, but initial treatment schedules vary. Injections are often given daily for a week, followed by once a week for one month, and then monthly. Because the response is variable, more frequent injections or higher oral doses are occasionally necessary to maintain normal B12 levels. People with irreversible causes of B12 deficiency require lifelong treatment.
Many experts recommend initial B12 shots for more rapid replacement, especially in severe cases with neurologic symptoms. A single 1,000 mcg injection will correct anemia and partially replete vitamin stores. Because they are less reliably absorbed, oral and nasal preparations are used only after correction of the deficiency, according to the journal "Blood."
B12 pills are often preferred for long-term treatment because they avoid the discomfort, inconvenience and cost of monthly injections. For others, however, a monthly injection is easier than remembering a daily medication. People can be taught to inject themselves which allows home treatment.
Extended release tablets which release B12 slowly over three to six hours may not be as well-absorbed. Newer preparations of B12 such as sublingual tablets, lozenges and nasal sprays have not been adequately studied, especially for correction of severe deficiency or long-term treatment.
B12 does not have toxic effects even at doses much higher than recommended. Because it is a water soluble vitamin, any excess not used by the body is excreted in the urine. Side effects are rare with either shots or pills. Pain or burning at the injection site is uncommon with small needles. Itching, skin rashes, and hives occur rarely with injections. Allergic reactions are possible with all forms of B12, and occasionally the preservative used in shots .