An essential cobalt-containing vitamin required for nerve myelination, DNA synthesis, and red blood cell maturation.
What it is
Vitamin B12 (cobalamin) is a complex organometallic compound containing a central cobalt ion sequestered within a tetrapyrrole corrin ring. In nutritional supplements, it is formulated as methylcobalamin, adenosylcobalamin, or synthetic cyanocobalamin. Vitamin B12 functions as an obligate metabolic coenzyme for methionine synthase (converting homocysteine to methionine) and L-methylmalonyl-CoA mutase (converting methylmalonyl-CoA to succinyl-CoA in mitochondrial energy production).
Also known as: Cobalamin, Methylcobalamin, Cyanocobalamin
What it does
- Cofactor for methionine synthase, enabling DNA methylation and homocysteine regulation.
- Drives red blood cell maturation in bone marrow, preventing megaloblastic anemia.
- Maintains myelin sheath integrity surrounding peripheral and central nerve fibers.
- Supports mitochondrial Krebs cycle energy production via succinyl-CoA synthesis.
Amplified by probiotics
Absorption of dietary vitamin B12 requires gastric intrinsic factor (IF) and specialized cubam receptor-mediated endocytosis in the terminal ileum. Certain probiotic species—such as Lactobacillus reuteri and Pseudomonas strains—possess the enzymatic machinery to synthesize cobalamin de novo. Microencapsulated probiotic delivery transports live strains into the distal gut, expanding total luminal cobalamin concentrations. Furthermore, probiotics suppress pathogenic ileal overgrowth that would otherwise compete for or degrade free cobalamin. Probiotic short-chain fatty acids also decrease mucosal inflammation in the terminal ileum, preserving healthy cubam receptor density and improving intrinsic factor-bound B12 uptake efficiency.
Typical dose
2.4–1,000 µg/day
The evidence
Evidence: strongExtensive human clinical trials prove that oral B12 supplementation effectively resolves neurological paresthesias, corrects megaloblastic anemia, and normalizes plasma methylmalonic acid and homocysteine. High oral doses (500–1,000 µg) utilize passive diffusion pathways independent of intrinsic factor (Green et al. 2017, Nat Rev Dis Primers; O'Leary & Samman 2010, Nutrients).
Safety & who should check first
Exceedingly high safety margin with no established upper limit (UL); non-toxic at high supplemental doses due to low saturable active transport and rapid excretion.