The energy grid's foreman. Keeps your nerves and brain healthy, makes red blood cells. Think of it as essential for your body's electrical wiring and oxygen delivery.
Reviewed March 2026
Public health figures for this ingredient, reported by the agencies that publish them, cited and dated.
USDA advises fortified foods or supplements after 50
In its national intake tables USDA notes that "it is advised that individuals over 50 meet their B12 requirement with fortified foods or supplements".
USDA ARS, Usual Nutrient Intake from Food and Beverages, by Gender and Age, WWEIA NHANES 2013-2016, Table A 26 (vitamin B12), table note. ↗About 11% of US girls aged 14 to 18
take in less vitamin B12 from food and drink than the estimated average requirement.
USDA ARS, Usual Nutrient Intake from Food and Beverages, by Gender and Age, WWEIA NHANES 2013-2016, Table A 26 (vitamin B12), females 14-18: 11% below EAR (SE 2.4). ↗About 8% of US women aged 19 and over
take in less vitamin B12 from food and drink than the estimated average requirement.
USDA ARS, Usual Nutrient Intake from Food and Beverages, by Gender and Age, WWEIA NHANES 2013-2016, Table A 26 (vitamin B12), females 19+: 8% below EAR (SE 1.2). ↗Population figures from public health data. Context for the category, not a statement about any individual and not a claim about this product.
Source: NIH ODS + Allen 2009 B12 review
A randomised, double-blind, parallel-group dose-finding trial in 120 older people with mild vitamin B12 deficiency, defined as serum B12 of 100 to 300 pmol/L with methylmalonic acid at or above 0.26 umol/L, gave daily oral cyanocobalamin at 2.5, 100, 250, 500 or 1000 ug for 16 weeks. Mean plasma methylmalonic acid fell 16%, 16%, 23%, 33% and 33% across those doses. Daily doses of 647 to 1032 ug accounted for 80% to 90% of the estimated maximum reduction. The window was measured on a blood marker of B12 status, not on a symptom.
Where a trial measured an actual number, we show it next to the claim. It is the average across the trials, never a promise about one person.
A further 7 percent reduction in plasma homocysteine on top of what folic acid achieves.
Adults already taking folic acid, with vitamin B12 at about 0.4 mg daily.
Read at the source. The magnitude sits beside the same trial the claim already cites. It describes what the trials measured, never what any one person will feel.
These words describe the research, not the molecule's worth. Research strength is how much work stands behind one claim, and it is never a product score.
Critical for life. Deficiency causes permanent damage.
A further 7 percent reduction in plasma homocysteine on top of what folic acid achieves.
Adults already taking folic acid, with vitamin B12 at about 0.4 mg daily. Confidence interval 95% CI 4 to 9 percent.
Why these belong in the same formula. Each row says what the basis is, from settled biochemistry through to a trial that measured the pair.
Vitamin B12 is the cofactor for methionine synthase, the enzyme that moves a methyl group from folate onto homocysteine to rebuild methionine. When B12 runs low that step stalls and folate stays stuck in its methyl form, so the two nutrients have to move together to keep methylation and DNA synthesis running.
B12 and folate rebuild methionine from homocysteine, while vitamin B6 is the cofactor for the other exit, the transsulfuration step that routes homocysteine toward cysteine. Because they cover complementary arms of the same pathway, the two are routinely formulated together to keep homocysteine within its normal range.
Making a red blood cell draws on both nutrients at different steps, with B12 and folate driving the DNA synthesis that lets precursor cells divide and iron building the hemoglobin that fills them. Because each carries a step the other cannot, supplying both supports normal red blood cell formation.
Methionine synthase reductase is an FAD enzyme that re-reduces the cobalamin cofactor after it oxidises, so riboflavin status sets how well the B12 enzyme keeps running. Riboflavin is a required partner rather than an optional extra.
Methionine synthase takes the methyl group from 5-methyltetrahydrofolate and passes it via cobalamin to homocysteine. Without enough B12 the folate pool stalls in the methyl form, which is why the two are dosed together.
Betaine homocysteine methyltransferase remethylates homocysteine using betaine instead of the folate and B12 route, so the two pathways share one substrate. Formulations combine them to support normal homocysteine handling from both directions.
The methionine that B12-dependent methionine synthase produces is adenylated to SAM, the cell's main methyl donor. SAM in turn regulates the cycle, so supply and demand for methyl groups are linked.
Choline is oxidised to betaine, feeding the same methyl group pool that the folate and cobalamin route supplies. When one route is short the other carries more of the load.
Adenosylcobalamin is the form that methylmalonyl-CoA mutase uses inside mitochondria, while methylcobalamin serves the cytosolic methylation route. Supplying both covers the two distinct cobalamin-dependent enzymes.
The cubam receptor that internalises the intrinsic factor and cobalamin complex in the ileum needs calcium ions to bind it. Calcium availability is part of the absorption step itself.
Adenosylcobalamin-dependent mutase clears propionyl-CoA from odd-chain fatty acids, and carnitine carries those acyl groups into mitochondria and buffers the excess as acylcarnitines. The two act on the same acyl-CoA pool.
Large ascorbate concentrations reduce and destroy cobalamin in solution, forming inactive analogues. Separating a high-dose ascorbate product from the cobalamin dose keeps the vitamin intact.
When a marked B12 shortfall is corrected, blood cell production restarts quickly and the new cells draw potassium out of the plasma. Serum potassium can fall during the first days of aggressive repletion, which is why it is monitored in that setting rather than assumed stable. This is a handling consideration during correction, not a reason to co-dose potassium routinely.
Methionine synthase uses methylcobalamin to move a methyl group from 5-methyltetrahydrofolate onto homocysteine, regenerating methionine. B12 status therefore sets how much dietary homocysteine is recycled back to methionine rather than lost. Supplemental methionine loads the same cycle from the other end.
Biotin is the cofactor for propionyl-CoA carboxylase, which makes methylmalonyl-CoA, and adenosylcobalamin is the cofactor for the mutase that converts methylmalonyl-CoA onward to succinyl-CoA. The two vitamins run consecutive steps of the same route out of odd-chain fatty acid and branched-chain amino acid catabolism. A shortfall in either raises pathway intermediates, which is why methylmalonic acid is read as a functional B12 marker rather than an outcome.
Betaine-homocysteine methyltransferase, the B12-independent route that remethylates homocysteine using betaine, is a zinc metalloenzyme. Zinc status therefore influences the backup pathway that operates alongside the B12-dependent one. The relationship is enzymatic rather than an absorption interaction.
Serine hydroxymethyltransferase transfers a carbon from serine onto tetrahydrofolate, which is the main entry point for the one-carbon units that eventually become the methyl group B12 hands to homocysteine. Serine availability feeds the pool that methionine synthase draws on. Established biochemistry, not a tested supplement combination.
The glycine cleavage system releases one-carbon units onto tetrahydrofolate and is a second feed into the same folate pool that methionine synthase uses with cobalamin. Glycine also accepts methyl groups through glycine N-methyltransferase, which is how surplus methylation capacity is disposed of. Both connections are biochemical rather than clinically tested as a pairing.
Homocysteine has two fates: remethylation to methionine, which needs B12 and folate, or transsulfuration to cysteine, which needs vitamin B6. Improving B12 status pushes more homocysteine down the remethylation branch, leaving relatively less substrate for cysteine and downstream glutathione synthesis. This is a flux shift between branches, not a shortage.
Endogenous creatine synthesis consumes a large share of the body's S-adenosylmethionine methyl groups. Supplying creatine from outside reduces that demand, which lowers the methylation load carried by the folate and B12 dependent remethylation cycle. The mechanism is well described; the size of any homocysteine effect from combining them is not established.
Cobalamin is made only by bacteria and archaea, and certain strains including some propionibacteria and lactobacilli synthesise it. Absorption of B12 in humans happens in the distal ileum through the intrinsic factor and cubam route, so colonic bacterial output is largely past the site of uptake. Whether a probiotic can meaningfully contribute to human B12 status has not been settled.
Most of the cobalamin-like material in spirulina is pseudovitamin B12, a corrinoid that human enzymes cannot use. These analogues can occupy binding proteins without carrying out the cofactor role, so a label figure for B12 from spirulina does not translate into functional B12. Anyone relying on spirulina as the B12 source is reading a number that overstates the active fraction.
Nothing specific on file for Vitamin B12. Match the label to the daily amount above, and tell your doctor what you take.
Not medical advice. Show the label to your pharmacist.B12 is a cobalt-containing molecule, and the body uses it in exactly two jobs: one in the cell fluid and one in the mitochondria.
B12 is the handoff point where a methyl group moves from folate onto homocysteine, turning it back into methionine.
Without enough B12, folate gets stuck in one form. Adding folate can tidy up the blood picture while the underlying B12 gap keeps going, which is why the two are assessed together.
A second B12 job clears a compound called methylmalonic acid. When B12 runs low that compound builds up, so labs measure it to judge B12 status.
Bacteria in large tanks make it, much like the way fermented foods are produced, and the tank is fed cobalt because cobalt sits at the centre of the molecule. The vitamin is then extracted, cleaned up, and mixed with a filler because the actual dose is only micrograms.
Built by fermentation, the same way vitamin B12 and many amino acids are made at scale. Controlled conditions, consistent output.
The fermentation medium supplies carbon and nitrogen plus a cobalt salt, because cobalt is the metal at the centre of the finished molecule and the bacteria cannot make it.
Industrial production uses cobalamin-producing bacteria, commonly Pseudomonas denitrificans or Propionibacterium freudenreichii, grown in large aerated or anaerobic tanks. No plant or animal makes B12; every dietary source traces back to bacterial synthesis.
Cells are collected and broken open, and the intracellular corrinoid is released into solution, typically with heat and a chemical release step.
The crude corrinoid is converted to a stable single species: treatment in the presence of cyanide gives cyanocobalamin, while a hydroxide route gives hydroxocobalamin. Methyl and adenosyl forms are produced by their own ligand-exchange chemistry.
The cobalamin is purified through resin or solvent steps and crystallised to a deep red powder of defined potency.
Because the active is potent at microgram doses, the crystal is usually diluted onto mannitol or a similar carrier to a low percentage so it can be blended and weighed accurately in a tablet or capsule.
The trituration is pressed, encapsulated, dissolved or prepared as a sterile solution, which is where the route rather than the molecule differs.
Labels rarely state the producing organism, whether the cyanide-route or hydroxide-route conversion was used, or the trituration percentage, all of which are ordinary manufacturing details rather than quality signals.
The whole-food sources on file. A supplement closes the gap, it does not replace dinner.
A gram-for-gram figure (how much of each you would eat to match a dose) will appear here once it is sourced and reviewed. This page will not print a number it cannot cite.
Same mineral in different salts. Each is its own molecule with its own page, and absorption and feel differ from one to the next.
These are the studies our verdict leans on, chosen from the 645 we read for Vitamin B12. The full linked list is below.
6 sources behind our Vitamin B12 verdict: peer-reviewed studies and registered clinical trials. Every one links straight to PubMed, the journal, or ClinicalTrials.gov. Read them yourself.
Evidence surfaced via Semantic Scholar (Allen Institute for AI) and ClinicalTrials.gov. Ranked by study type and citation weight, not cherry-picked.
Read this carefully. These are 274,942 voluntary, unverified reactions reported to the FDA (openFDA). The number mostly reflects how popular Vitamin B12 is, not how risky it is. A report is not proof Vitamin B12 caused anything. It is a signal of what to watch for, nothing more.
Source: openFDA adverse-event reports. Voluntary reporting, not an incidence rate.
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. This information is for educational purposes only and is not intended to diagnose, treat, cure, or prevent any disease. Consult your healthcare provider before starting any supplement regimen.
