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
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.
Alan R. Gaby, MD
1. Lederle FA. Oral cobalamin for pernicious anemia.
Medicine's best kept secret? JAMA 1991;265:94-95
2. Kuzminski AM , et al. Effective treatment of cobalamin
deficiency with oral cobalamin. Blood 1998;92:1191-1198.