Vitamin B12: injectable versus oral

Vitamin B12 is used therapeutically, both to correct vitamin B12 deficiency and for its apparent pharmacological effects. The vitamin is available in various forms for either oral or parenteral (typically intramuscular) administration. Preparations designed for sublingual or intranasal administration are also available, but they are relatively expensive and there is not much research on their use.

There appears to be some confusion among practitioners of natural medicine about whether oral or intramuscular administration is preferable for patients requiring vitamin B12 therapy. For the treatment of pernicious anemia, either method of treatment is acceptable. Although oral treatment is not common in the United States, as many as 40% of patients in Sweden with pernicious anemia are treated orally. Despite their lack of intrinsic factor and gastric hydrochloric acid, patients with pernicious anemia are capable of absorbing an average of 1.2% of an orally administered dose of cyanocobalamin._¹ An oral dose of 100-250 mcg/day will maintain adequate serum vitamin B12 levels in most patients with pernicious anemia, although some patients may require as much as 1,000 mcg/day. Therefore, patients with pernicious anemia who are being treated with oral vitamin B12 are generally advised to take 1,000 mcg/day. For those with newly diagnosed pernicious anemia, some doctors recommend an oral dose of 2,000 mcg/day (or injections) during the first month, in order to replenish body stores.

A year’s supply of 1,000-mcg vitamin B12 tablets costs under $20, which is less than the cost of going to the doctor’s office at least four times a year for injections. On the other hand, patients who are likely to be noncompliant with oral therapy should be seen regularly by a doctor and treated with intramuscular injections.

When vitamin B12 is being used for its pharmacological effects, as in the treatment of fatigue, Bell’s palsy, diabetic neuropathy, subdeltoid bursitis, or asthma, intramuscular injections appear to be preferable to oral administration. Although there is little published research in this area, clinical observations suggest that orally administered vitamin B12 is not particularly effective against these conditions. It appears that supraphysiological serum concentrations are usually needed for vitamin B12 to exert its pharmacological effects, and that these serum concentrations can be achieved only with parenteral administration.

Some writers have argued that vitamin B12 injections are unnecessary, citing a study that claimed oral vitamin B12 (2,000 mcg/day) produces higher serum vitamin B12 levels than intramuscular injections.²_ However, in that study, the serum concentrations were measured one month after the last intramuscular injection was given, whereas the oral doses were being taken daily during that time. Interestingly, although this study was published in a specialty journal (Blood), it contained the following disclaimer: “The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked ‘advertisement’ in accordance with 18 U.S.C. section 1734 solely to indicate this fact.” Although the study did confirm that oral vitamin B12 is effective for the treatment of vitamin B12 deficiency (including pernicious anemia), it did not compare oral and intramuscular administration with respect to their short-term (1-7 days) effects on serum levels. Consequently, this study cannot be used to justify the claim that oral vitamin B12 produces the same pharmacological effect as does intramuscular vitamin B12.

In summary, experimental and clinical evidence indicate that either oral or parenteral therapy can be used effectively for the treatment of vitamin B12 deficiency. However, when vitamin B12 is being used for its pharmacological effects, in the vast majority of cases only parenteral administration appears to be effective.