Wisdom Wednesday: Oral Vitamin B12 Versus Intramuscular Vitamin B12

Vitamin B12 deficiency is common, and the incidence increases with age. Most people with vitamin B12 deficiency are treated in primary care with intramuscular (IM) vitamin B12. Doctors may not be prescribing oral vitamin B12 formulations because they may be unaware of this option or have concerns regarding its effectiveness.

The goal of the review was to assess the effects of oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency.

The primary outcomes of data collection and analysis were serum vitamin B12 levels, clinical signs and symptoms of vitamin B12 deficiency, and adverse events. Secondary outcomes were health-related quality of life, acceptability to patients, hemoglobin and mean corpuscular volume, total homocysteine and serum methylmaloic acid levels.

Only three RCTs met our inclusion criteria. The trials randomized 153 participants (74 participants to oral vitamin B12 and 79 participants to IM vitamin B12). Treatment duration and follow-up ranged between three and four months. The mean age of participants ranged from 38.6 to 72 years. The treatment frequency and daily dose of vitamin B12 in the oral and IM groups varied among trials. The overall quality of evidence for this outcome was low due to serious imprecision (low number of trials and participants). In two trials employing 1000 ug/day oral vitamin B12, there was no clinically relevant difference in vitamin B12 levels when compared with IM vitamin B12. Orally taken vitamin B12 showed lower treatment associated costs than IM vitamin B12.

Low quality evidence shows oral and IM vitamin B12 having similar effects in terms of normalizing serum vitamin B12 levels. Further trials should conduct better randomization and blinding procedures, recruit more participants, and provide adequate reporting.



My Take:
The question of oral B12 versus IM B12 is a common one in my practice. Unfortunately, this review sheds little light on the subject as there were so few studies and they were poorly designed.

Clinically, I see significantly better outcomes using the oral vitamin B12 then IM injection. This is because most of IM vitamin B12 is in the food form, cyanocobalamin. I use methylcobalamin, one of bioavailable forms of vitamin B12. On occasion, and specifically with elite athletes, I use adenocobalamin, a less common bioavailable form of vitamin B12.

Cyanocobalamin in food is first reduced by removing the cyanide in the stomach. Then a water molecule replaces the cyanide through oxidation to create hydrocobalamin. Hydrocobalamin is then absorbed into the lining of the small intestine through active transport where the cells covert it to either methylcobalamin or adenocobalamin. Finally, it is released into the blood stream.
When cyanocobalamin is injected in a muscle where do these chemical conversions occur? I honestly don’t know the answer. It is thought that every cell in the body can convert a small amount of cyanocobalmin to the active forms for its’ own use. While that may be true, in a natural setting dietary cyanocobalamin never would be found in the blood stream. Unfortunately, measuring serum vitamin B12 levels do not distinguish between the various forms of vitamin B12.

The Bottom Line:
I recommend taking a bioavailable form of vitamin B12 as oral supplementation. A third of the population has genetic snippets that limit or prevent conversion of food sources of vitamin B12 to the bioavailable forms.

Along with Omega 3 fatty acids and vitamin D, methylcobalamin is the one of the most common supplements I recommend in my practice.

Source: March 15, 2018 The Cochrane Library