title: Comparative Bioavailability and Utilization of Particular Forms of B12Supplements With Potential to Mitigate B12-related Genetic Polymorphisms.
abstract: BACKGROUND
  Three natural forms of vitamin B12are commercially available: methylcobalamin (MeCbl), adenosylcobalamin (AdCbl), and hydroxycobalamin (OHCbl), all of which have been shown in clinical studies to improve vitamin B12status. They are bioidentical to the B12forms occurring in human physiology and animal foods. In contrast, cyanocobalamin (CNCbl), a synthetic B12compound 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 B12forms; (2) to determine whether supplementation with a particular B12form (or combination of forms) presents any advantages for the general population or for individuals with single nucleotide polymorphisms (SNPs) in B12-related pathways; and (3) to address misconceptions regarding B12forms, methylation pathways, and various SNPs reported in commercially available tests.
  
  
  METHODS
  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.
  
  
  METHODS
  The study occurred in Los Angeles, CA, USA.
  
  
  RESULTS
  The studies reviewed provide evidence that all supplemental or food-derived B12forms 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 B12ingested. 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 B12may be influenced by many factors such as gastrointestinal pathologies, age, and genetics. Polymorphisms on B12-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 B12(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 B12forms may likely have similar bioavailabilities and physiological effects; thus, it makes sense to employ the least-expensive form of B12, such as MeCbl. Individuals with particular single nucleotide polymorphisms (SNPs) affecting B12assimilation may raise their B12status more efficiently with 1 or more particular forms of vitamin B12. 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 B12at a time, or they might simply use a supplement with a combination of all 3 naturally occurring forms of B12that are commercially available for a better chance of achieving faster clinical results. That approach may or may not offset genetic polymorphisms involving B12metabolism and related pathways.
authors.affiliation: , is an independent nutrition research consultant in Los Angeles, California. , is vice president for health sciences division, the director of the Human Nutrition Institute, and an associate professor of clinical sciences at the University of Bridgeport in Bridgeport, Connecticut. He is also the chief medical officer for Designs for Health, Inc, in Suffield, Connecticut.
authors.forename: Cristiana
authors.initials: C
authors.lastname: Paul
authors.affiliation: , is an independent nutrition research consultant in Los Angeles, California. , is vice president for health sciences division, the director of the Human Nutrition Institute, and an associate professor of clinical sciences at the University of Bridgeport in Bridgeport, Connecticut. He is also the chief medical officer for Designs for Health, Inc, in Suffield, Connecticut.
authors.forename: David M
authors.initials: DM
authors.lastname: Brady