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Most people do not require vitamin B12 supplements. However, vegans should supplement with at least 2 to 3 mcg per day.
People with pernicious anemia are often treated with injections of vitamin B12. However, oral administration of 1,000 mcg per day can be used reliably as an alternative to vitamin B12 injections.228, 229, 230, 231, 232
Absorption of vitamin B12 is reduced with increasing age. Some research suggests that elderly people may benefit from 10 to 25 mcg per day of vitamin B12.233, 234, 235 One study of elderly people with vitamin B12 deficiency suggested that as much as 500 to 1,000 mcg of vitamin B12 per day might be necessary to achieve optimal vitamin B12 status.236 Vitamin B12 status was measured in this study using a sensitive laboratory test (the plasma methylmalonic acid concentration).
When vitamin B12 is used for therapeutic purposes other than correcting a deficiency, injections are usually necessary to achieve results.
Sublingual forms of vitamin B12 are available,237 but there is no proof that they offer any advantage to oral supplements.
Vitamin B12 is found in all foods of animal origin, including dairy, eggs, meat, poultry, and fish. According to one report, small, inconsistent amounts occur in seaweed (including nori and chlorella) and tempeh.238 Many researchers and healthcare professionals believe that people cannot rely on vegetarian sources to provide predictably sufficient quantities of vitamin B12. However, another study found substantial amounts of vitamin B12 in nori (at least 55 mcg per 100 grams of dry weight).239
Vegans (vegetarians who also avoid dairy and eggs) frequently become deficient, though the process often takes many years. People with malabsorption conditions, including those with tapeworm infestation and those with bacterial overgrowth in the intestines, often suffer from vitamin B12 deficiency. Malabsorption of vitamin B12 can also result from pancreatic disease, the effects of gastrointestinal surgery, or various prescription drugs.240
Pernicious anemia is a special form of vitamin B12 malabsorption due to impaired ability of certain cells in the stomach to make intrinsic factor—a substance needed for normal absorption of vitamin B12. By definition, all people with pernicious anemia are vitamin B12-deficient. They require either vitamin B12 injections or oral supplementation with very high levels (1000 mcg per day) of vitamin B12.
Older people with urinary incontinence241 and hearing loss242 have been reported to be at increased risk of B12 deficiency.
Infection with Helicobacter pylori, a common cause of gastritis and ulcers, has been shown to cause or contribute to adult vitamin B12 deficiency. H. pylori has this effect by damaging cells in the stomach that make hydrochloric acid—which is needed for normal absorption of vitamin B12. In one trial, H. pylori was detected in 56% of people with anemia due to vitamin B12 deficiency. Successful eradication of H. pylori led to improved blood levels of B12 in 40% of those infected.243 Other studies have also suggested a link between H. pylori infection and vitamin B12 deficiency.244, 245 Elimination of H. pylori infection does not always improve vitamin B12 status. People with H. pylori infections should have vitamin B12 status monitored.
In a preliminary report, 47% of people with tinnitus and related disorders were found to have vitamin B12 deficiencies that may be helped by supplementation.246
HIV-infected patients often have low blood levels of vitamin B12.247
A disproportionately high amount of people with psychiatric disorders are deficient in B12.248 Significant vitamin B12 deficiency is associated with a doubled risk of severe depression, according to a study of physically disabled older women.249
Although blood levels of vitamin B12 may be higher in alcoholics, actual body stores of vitamin B12 in the tissues (such as the liver) of alcoholics are frequently deficient.251, 252
Low blood levels of vitamin B12 are sometimes seen in pregnant women; however, this does not always indicate a vitamin B12 deficiency.253 The help of a healthcare professional is needed to determine when a true vitamin B12 deficiency exists in pregnant women with low blood levels of the vitamin.
Hydroxocobalamin (a form of vitamin B12) has been recognized for more than 40 years as an effective antidote to cyanide poisoning. It is currently being used in France for that purpose. Because of its safety, hydroxocobalamin is considered by some researchers to be an ideal treatment for cyanide poisoning.254
Cyanocobalamin, a synthetic form of vitamin B12 commonly found in supplements, is normally present only in trace amounts in the body. It has no known biological activity on its own, and must be converted by the body into active forms of vitamin B12. Supplementing with hydroxocobalamin, another form of vitamin B12, results in more sustained levels of vitamin B12 in the body compared with cyanocobalamin and can be used for conditions such as cyanide poisoning (cyanocobalamin should not be used for cyanide poisoning). Partly for these reasons, hydroxocobalamin is to be preferred as a vitamin B12 supplement over cyanocobalamin. Other acceptable forms of vitamin B12 include methylcobalamin and adenosylcobalamin, although there is no clear evidence that these forms (except in very rare cases) are preferable to hydroxocobalamin.255
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The information presented by Healthnotes is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. Self-treatment is not recommended for life-threatening conditions that require medical treatment under a doctor's care. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires June 2017.