Comparative Bioavailability and Utilization of Particular Forms of B Supplements With Potential to Mitigate B-related Genetic Polymorphisms.

CONTEXT

Three natural forms of vitamin B are commercially available: methylcobalamin (MeCbl), adenosylcobalamin (AdCbl), and hydroxycobalamin (OHCbl), all of which have been shown in clinical studies to improve vitamin B status. They are bioidentical to the B forms occurring in human physiology and animal foods. In contrast, cyanocobalamin (CNCbl), a synthetic B compound used for food fortification and in some supplements, occurs only in trace amounts in human tissues as a result of cyanide intake from smoking or other sources.

OBJECTIVE

This study had 3 objectives: (1) To summarize and compare assimilation pathways for 4 B forms; (2) to determine whether supplementation with a particular B form (or combination of forms) presents any advantages for the general population or for individuals with single nucleotide polymorphisms (SNPs) in B-related pathways; and (3) to address misconceptions regarding B forms, methylation pathways, and various SNPs reported in commercially available tests.

DESIGN

PubMed was systematically searched for articles published up to June 2016 using specific key words. Human, animal, and in vitro studies that were published in English, French, and German were included. Other studies considered were found by selecting in PubMed the suggested "related studies" and also some referenced studies.

SETTING

The study occurred in Los Angeles, CA, USA.

RESULTS

The studies reviewed provide evidence that all supplemental or food-derived B forms are reduced to a core cobalamin molecule, which converts to the intracellular active forms: MeCbl and AdCbl, in a ratio not influenced by the form of B ingested. The methyl and adenosyl components of supplemental MeCbl and AdCbl are cleaved inside cells and are not used in the synthesis of intracellular MeCbl and AdCbl, respectively. However, the overall bioavailability of each form of supplemental B may be influenced by many factors such as gastrointestinal pathologies, age, and genetics. Polymorphisms on B-related pathways may affect the efficiency of absorption, blood transport, cellular uptake, and intracellular transformations.

CONCLUSIONS

Supplementing with any of the nature bioidentical forms of B (MeCbl, OHCbl, and/or AdCbl) is preferred instead of the use of CNCbl, owing to their superior bioavailability and safety. For the majority of the population, all B forms may likely have similar bioavailabilities and physiological effects; thus, it makes sense to employ the least-expensive form of B, such as MeCbl. Individuals with particular single nucleotide polymorphisms (SNPs) affecting B assimilation may raise their B status more efficiently with 1 or more particular forms of vitamin B. However, because those types of SNPs are not currently reported in commercial tests, individuals may require either a trial-and-error approach by supplementing with 1 particular form of B at a time, or they might simply use a supplement with a combination of all 3 naturally occurring forms of B that are commercially available for a better chance of achieving faster clinical results. That approach may or may not offset genetic polymorphisms involving B metabolism and related pathways.