Response to letters about vitamin B12

We thank Drs Rosenberg and Vitou for their letters^1,2 pertaining to our article, “Oral vitamin B12: a cost-effective alternative.”³ We would like to clarify a few of the statements. First, Dr Rosenberg raises the concern that B vitamins increase the risk of cancer and mortality. A systematic review of 12 randomized controlled trials (including the study Dr Rosenberg referenced) that enrolled more than 47 000 patients concluded that B vitamins do not increase the risk of cancer or mortality (and also do not prevent cardiovascular disease).⁴

Next, we do agree with Dr Vitou that some patients who do not have vitamin B12 (VB12) deficiency might feel less fatigued when they receive intramuscular VB12 injections. Of interest, it appears that the only high-level evidence supporting this practice was a small crossover controlled trial of 28 patients published more than 40 years ago.⁵ In this study of relatively young, mostly female, non-anemic patients, both intramuscular VB12 injections and placebo improved general symptoms, including fatigue and overall well-being.

We believe that VB12 therapy should be reserved for patients with documented VB12 deficiency and not for cardiovascular disease prevention, for patients with cognitive impairment,⁶ or for patients with general fatigue. Best evidence suggests that VB12 does not increase cancer or mortality rates.

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