Swallow your pride

I must comment on your otherwise excellent and enjoyable article on vitamin B12 in the April issue of Canadian Family Physician,1 which repeats the fallacy that the only treatment for pernicious anemia is lifelong vitamin B12 injections. In fact, there is high-quality evidence that—even in pernicious anemia—sufficient amounts of vitamin B12 can be absorbed orally when large enough doses are given. Absorption occurs by diffusion, even in the total absence of intrinsic factor.

Some experts recommend parenteral vitamin B12 for neurologic complications of B12 deficiency, and multiple parenteral doses to replenish the body stores. In symptomatic individuals, it is also reasonable to give 1 parenteral dose at the same time that you initiate oral treatment. However, in neither state is it necessary to continue lifelong injection treatment. In individuals lacking intrinsic factor (or for any other form of malabsorption), the amount of B12 passively absorbed from 500 μg taken orally per day is equivalent to a 1000 μg injection per month.

The daily recommended requirement of vitamin B12 is 2.5 μg. If 1% of a 500 μg dose is absorbed, the absorbed amount equals 5 μg (double the daily recommended requirement). I usually prescribe 1000 μg of vitamin B12 daily, which is more than sufficient and allows for the occasional missed dose. Once treatment has commenced, it is not necessary to check serum levels of vitamin B12. I have occasionally done so, and the levels are invariably in the upper physiologic range or even higher.

As a general practitioner, I often have to send this evidence to consultants who attempt to return my patients taking oral vitamin B12 to injection treatment. In an age of reduced patient and physician time, with financial strains on the health care system, this simple change to oral treatment can be beneficial.

Authors of a recent Cochrane review stated that “Vitamin B12 is rarely prescribed in the oral form in most countries, other than Canada and Sweden, where such replacement recently accounted for 73% of the total vitamin B12 prescribed. Possible reasons for doctors not prescribing oral formulations include unawareness of this option or concerns regarding effectiveness due to unpredictable absorption.”2

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