Overview
Water-soluble cobalt-containing vitamin found almost exclusively in animal products; deficiency is common in vegans and older adults.
- Beef liver
- Clams
- Sardines
- Eggs
- Fortified plant milks
- Methylcobalamin (active)
- Cyanocobalamin (stable)
- Hydroxocobalamin (injectable)
- Adenosylcobalamin
Forms & variants of Vitamin B12
Different chemical forms of Vitamin B12 behave differently. Browse each form's mechanism, bioavailability, and best-use context.
Active methyl-form of B12 — directly usable in the methylation cycle.
Mitochondrial coenzyme form of B12 — partners with methylcobalamin for full B12 status.
Long-acting injectable form of B12 — used clinically for deficiency and cyanide poisoning.
Mechanism of action
Cofactor for methionine synthase (methylation cycle) and methylmalonyl-CoA mutase (fatty acid metabolism).
- · Methylation (homocysteine → methionine)
- · Myelin synthesis
- · Methionine synthase
- · Methylmalonyl-CoA mutase
Effects on the body
Organ system effects
Required for myelin; deficiency causes peripheral neuropathy.
Evidence-based benefits
Resolves megaloblastic anemia
Strong evidenceReverses neuropathy in deficient patients
Strong evidenceImproves fatigue (only if deficient)
Moderate evidencePotential side effects
- · Acne (rare)
Drug interactions
Supplement interactions
- FolateMethylation cycle partners.
No specific avoidances listed.
Dosing & bioavailability
Where to buy
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Third-party testedIndependently verified Vitamin B12 — look for USP, NSF, or Informed Sport seals on the label for purity and dose accuracy.Vitamin B12 third party tested NSF
CapsulesPre-measured Vitamin B12 capsules — easiest for travel and consistent daily dosing without scoops or scales.Vitamin B12 capsules
PowderBulk unflavored Vitamin B12 powder — best cost-per-gram and flexible dosing for stacking or mixing into drinks.Vitamin B12 powder unflavored
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B12 deficiency prevalence in vegetarians
Pawlak R, et al.
Review of B12 status across diet patterns.
Up to 86% of vegans showed deficiency without supplementation.
PubMed: Vitamin B12 — Resolves megaloblastic anemia
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PubMed: Vitamin B12 — Reverses neuropathy in deficient patients
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PubMed: Vitamin B12 — Improves fatigue
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PubMed: Vitamin B12 — randomized controlled trial
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PubMed: Vitamin B12 — meta-analysis
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PubMed: Vitamin B12 — pharmacokinetics
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PubMed: Vitamin B12 — safety adverse events
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PubMed: Vitamin B12 — dose response
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Google Scholar: Vitamin B12 — clinical evidence
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Cross-database citation index for Vitamin B12 as it relates to "clinical evidence".
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