Inherited and acquired vitamin B12 deficiencies: Which administration route to choose for supplementation?

Abstract

Vitamin B12 or cobalamin deficiency is a commonly encountered clinical scenario and most clinicians will have familiarity prescribing Vitamin B12 to treat their patients. Despite the high prevalence of this condition, there is widespread heterogeneity regarding routes, schedules and dosages of vitamin B12 administration. In this review, we summarise the complex metabolic pathway of Vitamin B12, the inherited and acquired causes of Vitamin B12 deficiency and subsequently highlight the disparate international practice of prescribing Vitamin B12 replacement therapy. We describe the evidence base underpinning the novel sublingual, intranasal and subcutaneous modes of B12 replacement in comparison to intramuscular and oral routes, with their respective benefits for patient compliance and cost-saving.

Keywords: cobalamin; cyanocobalamin; hydroxocobalamin; metabolic; vitamin B12.

FIGURE 1

Vitamin B12 absorption pathways and main factors and organs involved: Receptor-mediated absorption processes shown as sequential steps (A–D) with black arrows and Passive diffusion process outlined with red, dashed arrow. Detailed description of pathway outlined in text. Adapted from “Human Anatomy, Digestive System,” by BioRender.com (2022). Retrieved from https://app.biorender.com/biorender-icons.https://app.biorender.com/biorender-icons

FIGURE 2

Summary of intracellular metabolism of transcobalamin. Detailed description of pathway found in text.