From the Guidelines
Methylcobalamin and cyanocobalamin oral supplements are generally best absorbed in the gut, with methylcobalamin often being the preferred form for most people. The absorption of vitamin B12 involves several steps, including the release from proteins, binding to R-protein, and then to intrinsic factor, followed by receptor-mediated endocytosis in the terminal ileum 1.
- Key factors influencing absorption include the presence of gastric acid, pepsin, and intrinsic factor, as well as the integrity of the ileal mucosa.
- For individuals with normal digestive function, a standard oral dose of 1,000-2,000 mcg daily is typically sufficient to maintain adequate B12 levels.
- Methylcobalamin is the active form of B12 that's ready for immediate use by the body, while cyanocobalamin must be converted first but is generally more stable and less expensive.
- It's worth noting that taking B12 supplements with a meal containing some fat can enhance absorption, as B12 is fat-soluble, and regular monitoring of B12 levels through blood tests is advisable when treating a deficiency to ensure the supplement is effectively raising your levels 1.
- In cases of absorption issues, such as pernicious anemia, atrophic gastritis, or gastric bypass surgery, sublingual forms or B12 injections may be more effective alternatives.
From the Research
Oral Vitamin B12 Absorption
The absorption of oral vitamin B12 supplements in the gut is a complex process. According to 2, three natural forms of vitamin B12 are commercially available: methylcobalamin (MeCbl), adenosylcobalamin (AdCbl), and hydroxycobalamin (OHCbl). These forms have been shown to improve vitamin B12 status in clinical studies.
Comparison of B12 Forms
The study 2 compared the assimilation pathways for four B12 forms, including cyanocobalamin (CNCbl), a synthetic B12 compound. The results suggest that all supplemental or food-derived B12 forms are reduced to a core cobalamin molecule, which converts to the intracellular active forms: MeCbl and AdCbl. The overall bioavailability of each form of supplemental B12 may be influenced by factors such as gastrointestinal pathologies, age, and genetics.
Factors Affecting Absorption
Some key factors that affect the absorption of oral vitamin B12 supplements include:
- Gastrointestinal pathologies
- Age
- Genetics, including single nucleotide polymorphisms (SNPs) on B12-related pathways
- The form of B12 ingested, with natural forms (MeCbl, OHCbl, and AdCbl) preferred over synthetic forms (CNCbl) due to their superior bioavailability and safety
Recommended Forms of B12
Based on the study 2, supplementing with any of the natural bioidentical forms of B12 (MeCbl, OHCbl, and/or AdCbl) is preferred. For the majority of the population, all B12 forms may likely have similar bioavailabilities and physiological effects, making MeCbl a suitable choice due to its lower cost. However, individuals with particular SNPs affecting B12 assimilation may benefit from supplementing with one or more specific forms of vitamin B12.