Vitamin B12
An essential vitamin required for DNA synthesis, nerve function (myelin maintenance), and red blood cell formation. Deficiency is common, particularly in vegans, the elderly, those on metformin or proton pump inhibitors, and individuals with pernicious anemia. Injectable forms bypass the complex gut absorption pathway, making them the treatment of choice for severe deficiency and malabsorption.
Dosage
Deficiency: 1000 mcg IM weekly then monthly. Oral: 500-2000 mcg daily
Dosages shown are for research reference only. Always consult a qualified healthcare provider.
Half-Life
Hepatic stores last years; circulating methylcobalamin: 144 hours (6 days)
Half-Life Calculator →Administration
Intramuscular injection, subcutaneous injection, oral, or sublingual
Shop Research-Grade Peptides
99%+ purity · US-based · third-party lab tested
Getting Started — Here's What You'll Need
Effects
Nerve Function
Essential for myelin synthesis and maintenance — deficiency causes irreversible neuropathy.
Red Blood Cell Formation
Required for DNA synthesis in erythroid precursors — prevents megaloblastic anemia.
Energy Metabolism
Cofactor for methionine synthase and methylmalonyl-CoA mutase.
Mechanism of Action
Vitamin B12 (cobalamin) is a large organometallic molecule with a cobalt ion at its center, coordinated within a corrin ring. It is the most structurally complex vitamin and the only one containing a metal ion. Humans cannot synthesize B12 — it is produced exclusively by certain bacteria and archaea, and enters the human diet through animal products or bacterial fermentation. Absorption requires intrinsic factor (produced by gastric parietal cells), which binds B12 in the ileum for receptor-mediated endocytosis via the cubam receptor complex.
B12 functions as a cofactor for two essential enzymes. Methionine synthase (MS) uses methylcobalamin (methylB12) to catalyze the transfer of a methyl group from methyltetrahydrofolate (methyl-THF) to homocysteine, producing methionine and regenerating tetrahydrofolate (THF). This reaction sits at the intersection of two critical pathways: methionine is converted to S-adenosylmethionine (SAM), the universal methyl donor for DNA methylation, histone modification, neurotransmitter synthesis, and hundreds of other methylation reactions; and THF regeneration is essential for folate cycling and de novo nucleotide synthesis (required for DNA replication). B12 deficiency traps folate as methyl-THF ('methyl trap'), blocking DNA synthesis and causing megaloblastic anemia — red blood cell precursors cannot replicate their DNA properly, producing abnormally large, non-functional cells.
Methylmalonyl-CoA mutase uses adenosylcobalamin (adenosylB12) in mitochondria to convert methylmalonyl-CoA to succinyl-CoA, a key step in the catabolism of odd-chain fatty acids, branched-chain amino acids, and cholesterol. Deficiency causes methylmalonic acid accumulation, which is toxic to neurons and contributes to the peripheral neuropathy, subacute combined degeneration of the spinal cord, and cognitive decline seen in B12 deficiency. The neurological damage occurs because myelin synthesis requires both SAM-dependent methylation reactions (for phospholipid synthesis) and proper fatty acid metabolism (for myelin lipid composition), both of which depend on B12. Neurological damage from severe B12 deficiency can become irreversible if not treated promptly, which is why injectable B12 (which bypasses absorption barriers) is preferred for deficiency treatment.
Regulatory Status
Available over the counter as supplement. Injectable forms by prescription or through clinics. Multiple forms: cyanocobalamin, methylcobalamin, hydroxocobalamin.
Risks & Safety
Common
injection site pain, brief diarrhea.
Rare
acne, allergic reactions to cyanocobalamin formulation, itching, blood clots.
Compare Vitamin B12 With
Research Papers
30Published: January 26, 2026
AI Summary
Crystal structures revealed how a vitamin B12-dependent enzyme performs repeated methylations to build antibiotic-like molecules. The work clarifies how the enzyme switches between different chemical steps.
Published: December 31, 2025
AI Summary
A scoping review found that non-catecholamine drugs like hydroxocobalamin can restore blood pressure in vasoplegic syndrome after heart surgery. These agents may help when standard drugs fail.
Published: December 13, 2025
AI Summary
A review covers causes and management of low neutrophil counts, including vitamin B12 and folate deficiency. It outlines when to test, treat, and when febrile neutropenia needs urgent care.
Published: February 4, 2026
AI Summary
A review evaluates adjuncts for nerve repair, including methylcobalamin. It focuses on clinical utility and limitations rather than speculative mechanisms.
Published: January 5, 2026
AI Summary
A consensus panel identified a minimal set of blood tests for hypertension monitoring: eGFR, HbA1c, potassium, and sodium. Routine vitamin B12 testing lacked consistent evidence of benefit.
Published: December 2, 2025
AI Summary
High-dose vitamin B12 reduced early diabetic kidney damage in mice and shifted clock gene expression. The findings suggest B12 may protect the kidney partly through circadian regulation.
Published: March 25, 2026
AI Summary
Diabetic neuropathy was linked to higher IL-6, lower vitamin B12, and worse lipid profiles. IL-6 and nerve conduction studies may serve as early biomarkers and treatment targets.
Published: December 7, 2025
AI Summary
Researchers examined how often anemia occurs in acromegaly and what drives it. The abstract states the aim; full results would include vitamin B12 and other causes.
Published: January 26, 2026
AI Summary
Vitamin B12 nanocapsules protected rat kidneys from vancomycin toxicity by reducing oxidative stress, inflammation, and scarring. The nano-form may improve B12 delivery and kidney protection.
Published: January 9, 2026
AI Summary
Lipid nanocarriers loaded with vitamin B12 or cyclosporine reduced acute and chronic skin inflammation in mice. The formulations improved drug delivery through the skin.
Published: October 31, 2025
AI Summary
A review discusses serological strategies for diagnosing autoimmune metaplastic atrophic gastritis, which often causes B12 deficiency. The abstract notes diagnostic criteria are not standardized.
Published: September 29, 2025
AI Summary
A retrospective study evaluated treatment response in dogs with chronic intestinal inflammation. The abstract states the aim; full results would include B12 and dietary interventions.
Published: December 27, 2025
AI Summary
A meta-analysis assessed whether serum biomarkers predict gastric lesion risk in autoimmune gastritis. The abstract states the aim; full findings would clarify B12's prognostic role.
Published: October 19, 2025
AI Summary
Researchers compared BDNF and micronutrient status in diabetic patients with and without kidney disease. The abstract states the aim; full results would include B12 levels.
Published: October 16, 2025
AI Summary
Kisspeptin levels were compared in infertile and miscarrying women, with links to folate pathway genes and biochemical markers. The abstract states the aim; full results would include B12.
Published: October 20, 2025
AI Summary
Researchers tested whether vitamin B12 levels affect IVF pregnancy outcomes. The abstract states the aim; full findings would show whether B12 predicts success.
Published: September 30, 2025
AI Summary
Genomic analysis showed Endozoicomonas bacteria cannot make or transport vitamin B12, so they likely do not supply it to host organisms. The work clarifies their nutritional role.
Published: October 14, 2025
AI Summary
Nanofibers with vitamin B12 boosted nerve growth factor production and supported nerve cell differentiation. The scaffold may help repair peripheral nerve damage.
Published: October 21, 2025
AI Summary
A cobalt-containing natural product was discovered that inhibits coronavirus protease and blocks SARS-CoV-2 replication. It is the first such compound besides vitamin B12.
Published: September 24, 2026
AI Summary
A review links the anti-aging protein Klotho to micronutrient signaling and kidney health. The abstract describes the paradigm; full text would include B12 and related pathways.
Published: September 17, 2025
AI Summary
Vitamin B12 and G-CSF reduced cisplatin's ability to kill breast cancer cells in lab studies. The finding suggests supportive care may sometimes blunt chemotherapy; clinical studies are needed.
Published: June 29, 2025
AI Summary
Vitamin B12 improved adrenal gland function in hypothyroid rats. The abstract states the aim; full results would show whether B12 helps adrenal disturbances in hypothyroidism.
Published: September 1, 2025
AI Summary
Coating probiotics and vitamin B12 with pH-responsive polymers preserved viability and allowed controlled release in the gut. The approach may improve fortified foods.
Published: September 17, 2025
AI Summary
A case series describes TEMPI syndrome in Waldenström's macroglobulinemia. The abstract notes B12 and erythrocytosis; full details would cover diagnosis and treatment.
Published: May 15, 2025
AI Summary
A review describes liposomal delivery of nutrients including vitamin B12. Evidence suggests liposomal B12 may improve absorption compared with some conventional forms.
Published: June 28, 2025
AI Summary
Researchers measured vitamin B12 levels in children with type 1 diabetes. The abstract states the aim; full results would show how often deficiency occurs.
Published: July 10, 2025
AI Summary
A review covers edible insects as a sustainable source of protein, minerals, and vitamins including B12. It integrates nutritional, bioactive, and technical aspects.
Published: July 2, 2025
AI Summary
Kanamycin interfered with phage infection of E. coli when phages use the B12 transporter BtuB. The work shows antibiotic-phage interactions can depend on phage receptors.
Published: May 21, 2025
AI Summary
Oat-based probiotics reduced inflammation and improved some metabolic markers; vitamin B12 and cortisol showed promising changes. The study supports non-dairy probiotic concepts.
Published: July 8, 2025
AI Summary
A vitamin B12-dependent enzyme was found to cross-link amino acids in peptide antibiotics. The work expands known roles of B12 enzymes in natural product biosynthesis.
Frequently Asked Questions
What is Vitamin B12?
An essential vitamin required for DNA synthesis, nerve function (myelin maintenance), and red blood cell formation. Deficiency is common, particularly in vegans, the elderly, those on metformin or proton pump inhibitors, and individuals with pernicious anemia. Injectable forms bypass the complex gut absorption pathway, making them the treatment of choice for severe deficiency and malabsorption.
What is Vitamin B12 used for?
An essential vitamin required for DNA synthesis, nerve function (myelin maintenance), and red blood cell formation. Deficiency is common, particularly in vegans, the elderly, those on metformin or proton pump inhibitors, and individuals with pernicious anemia. Injectable forms bypass the complex gut absorption pathway, making them the treatment of choice for severe deficiency and malabsorption.
What is the dosage for Vitamin B12?
Deficiency treatment: 1000 mcg intramuscular once weekly for 4-8 weeks, then 1000 mcg intramuscular once monthly for maintenance. Oral: 500-2000 mcg once daily. Sublingual: 1000-5000 mcg once daily. Pernicious anemia requires lifelong intramuscular injections.
What are the side effects of Vitamin B12?
Common: injection site pain, brief diarrhea. Rare: acne, allergic reactions to cyanocobalamin formulation, itching, blood clots.
How does Vitamin B12 work?
Vitamin B12 (cobalamin) is a large organometallic molecule with a cobalt ion at its center, coordinated within a corrin ring. It is the most structurally complex vitamin and the only one containing a metal ion. Humans cannot synthesize B12 — it is produced exclusively by certain bacteria and archaea, and enters the human diet through animal products or bacterial fermentation. Absorption requires intrinsic factor (produced by gastric parietal cells), which binds B12 in the ileum for receptor-mediated endocytosis via the cubam receptor complex. B12 functions as a cofactor for two essential enzymes. Methionine synthase (MS) uses methylcobalamin (methylB12) to catalyze the transfer of a methyl group from methyltetrahydrofolate (methyl-THF) to homocysteine, producing methionine and regenerating tetrahydrofolate (THF). This reaction sits at the intersection of two critical pathways: methionine is converted to S-adenosylmethionine (SAM), the universal methyl donor for DNA methylation, histone modification, neurotransmitter synthesis, and hundreds of other methylation reactions; and THF regeneration is essential for folate cycling and de novo nucleotide synthesis (required for DNA replication). B12 deficiency traps folate as methyl-THF ('methyl trap'), blocking DNA synthesis and causing megaloblastic anemia — red blood cell precursors cannot replicate their DNA properly, producing abnormally large, non-functional cells. Methylmalonyl-CoA mutase uses adenosylcobalamin (adenosylB12) in mitochondria to convert methylmalonyl-CoA to succinyl-CoA, a key step in the catabolism of odd-chain fatty acids, branched-chain amino acids, and cholesterol. Deficiency causes methylmalonic acid accumulation, which is toxic to neurons and contributes to the peripheral neuropathy, subacute combined degeneration of the spinal cord, and cognitive decline seen in B12 deficiency. The neurological damage occurs because myelin synthesis requires both SAM-dependent methylation reactions (for phospholipid synthesis) and proper fatty acid metabolism (for myelin lipid composition), both of which depend on B12. Neurological damage from severe B12 deficiency can become irreversible if not treated promptly, which is why injectable B12 (which bypasses absorption barriers) is preferred for deficiency treatment.
How is Vitamin B12 administered?
Vitamin B12 is administered via intramuscular injection, subcutaneous injection, oral, or sublingual.
What is the half-life of Vitamin B12?
The half-life of Vitamin B12 is Hepatic stores last years; circulating methylcobalamin: 144 hours (6 days).
Is Vitamin B12 legal?
Available over the counter as supplement. Injectable forms by prescription or through clinics. Multiple forms: cyanocobalamin, methylcobalamin, hydroxocobalamin.
Related Peptides
5-Amino-1MQ
A pill that aims to switch fat cells from 'storage mode' to 'burning mode' by blocking an enzyme (NNMT) that is overactive in the fat tissue of overweight people. Not technically a peptide, but commonly sold alongside them. Unlike appetite suppressants, this targets the fat cells directly rather than making you eat less. The science is promising in lab studies, but there are no completed human trials yet.
AICAR
A natural compound that activates your cells' energy sensor — the same pathway that turns on during exercise. Mimics the metabolic effects of endurance exercise at the cellular level, helping with fat burning, glucose uptake, and building more mitochondria. Banned by WADA as a metabolic modulator after detection in professional cycling.
GLP-1
The natural appetite hormone that your gut produces after eating — it's what all GLP-1 weight loss drugs (semaglutide, tirzepatide, etc.) are designed to copy. Your body makes it naturally, but it breaks down within 1-2 minutes, which is far too fast to use as a medicine. That's why drug companies created modified versions that last days instead of minutes. Included here because understanding GLP-1 is key to understanding the entire class of modern weight loss drugs.
Humanin
A 24-amino-acid peptide naturally produced by mitochondria. Related to MOTS-c but works differently. Protects cells against oxidative stress, cell death, and age-related damage by interacting with proteins involved in apoptosis and IGF signaling. One of the most studied peptides in longevity research, with evidence that levels decline in aging tissues.