Vitamin B12

Cobalamin · also called Cobalamin, cyanocobalamin, vitamina B12, cobalamina

Vitamin B12 is an essential vitamin the body needs for red blood cells and healthy nerves. It comes naturally from animal foods such as shellfish, liver, fish, meat, eggs and dairy, and from fortified foods. Research is strongest for treating and understanding deficiency; evidence is weak or against for memory, mood and heart benefits in people who are not low. Low B12 can damage nerves, so see a doctor about symptoms before guessing.

General information, not medical advice. Last substantive update October 26, 2026 · Not medically reviewed. A named clinician has not signed off on this page. How this page is made

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About Vitamin B12

Vitamin B12 is an essential vitamin found naturally in animal foods. It is needed for red blood cells and nerves. Pills and injections help people who are deficient; trials do not show extra benefit for memory, mood or the heart in people who are not.

What vitamin B12 is

Vitamin B12, also called cobalamin, is a water-soluble B vitamin. MedlinePlus says it is important for protein metabolism and helps form red blood cells and maintain the nervous system. The NHS adds that it helps release energy from food and helps the body use folate. Leftover amounts leave the body in the urine, and the liver stores a few years' worth.

B12 comes in different forms. Cyanocobalamin is the name MedlinePlus lists. In the UK, B12 injections use hydroxocobalamin, which the NHS prefers because it stays in the body longer. Methylcobalamin (also called mecobalamin) is sold as a supplement. No head-to-head trial was read showing one form works better than another.

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Where B12 comes from in food

B12 occurs naturally in animal foods only. USDA data (per 3 oz or 85 g cooked portion unless stated): clams about 84.1 mcg; beef liver, braised, about 60.0 mcg; rainbow trout about 3.5 mcg; farmed salmon about 2.4 mcg; light tuna canned in water about 2.2 mcg; a broiled beef patty about 2.2 mcg. One cup of 2% milk has about 1.3 mcg; an 8 oz tub of plain low-fat yogurt about 1.3 mcg; an ounce of Swiss cheese about 0.9 mcg; one large egg about 0.6 mcg.

MedlinePlus says B12 is not present in plant foods unless fortified. Fortified breakfast cereals and some nutritional yeast products can contain it. In the USDA file, ready-to-eat cereals ranged from none to about 3 mcg in one serving, so the label matters. The B12 added to fortified foods is very easy for the body to absorb (MedlinePlus).

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Who is most often low in B12

MedlinePlus says deficiency is most common in people over 50, people on vegetarian or vegan diets, people who have had stomach or intestinal surgery, people with coeliac or Crohn disease, and people with pernicious anaemia. In pernicious anaemia the immune system attacks the stomach cells that make intrinsic factor, which B12 needs in order to be absorbed. The NHS says this is the most common cause in the UK and that around 1 in 10 people aged 75 or over are affected by B12 or folate deficiency.

Some medicines are linked to lower B12. In a 2022 review, B12 deficiency was found in 23% of people with type 2 diabetes on metformin and 17% of those not on it. Acid-reducing medicines (PPIs) showed a smaller link in a 2023 review, with results that varied. Signs of low B12 have many causes, so a blood test and a doctor are needed.

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What the research shows

The strongest facts are about deficiency: B12 is essential, shortage is harmful, and treating real deficiency works. Tablets and injections both raise blood B12 in the small trials available. For people who are not deficient, the research is mostly disappointing: no good evidence of benefit for memory, mood or energy, no change in heart attacks or deaths (a small drop in stroke from vitamin combinations), and no bone benefit.

Many trials give B12 together with folate and B6, so the effect of B12 alone is often unknown. Evidence for nerve damage and pregnancy outcomes is weak. Food and pills are not the same, and trial results for pills do not describe what food does.

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At a glance

Traditional uses history, not proof

An essential nutrient from animal foods and fortified foods
Sold as tablets, lozenges and injections for tiredness and low B12

Studied for research

Nutrient role, food sources and deficiency, high certainty
Low B12 on vegetarian and vegan diets and with metformin, low certainty
Tablets versus injections for deficiency, low certainty
Memory and thinking, low certainty
Depression and heart attack: no benefit found; small stroke effect from combinations
Nerve damage, pregnancy and bone health, low or very low certainty

Main compounds

Cyanocobalamin
Hydroxocobalamin (used for injections in the UK)
Methylcobalamin (mecobalamin)

Common forms

Food sources (shellfish, liver, fish, meat, eggs, dairy)
Fortified cereals, yeast products and soy products
Tablets, lozenges, nasal gel and injections (prescription forms are given by a clinician)

Research links: 2018 Cochrane review: oral versus injected B12 for deficiency · 2022 meta-analysis: metformin and B12 deficiency · 2021 review: B12 for thinking, mood and tiredness · 2017 Cochrane review: homocysteine-lowering vitamins and heart events · 2024 Cochrane review: B12 in pregnancy · Research Library · Genes & Biomarkers Library

What it is and its history

Accepted scientific name: Vitamin B12 (cobalamin), an essential water-soluble vitamin
Common names: Vitamin B12 (English); Cobalamin (English); Cyanocobalamin (English (one form; MedlinePlus lists it as an alternative name)); Vitamina B12 (Spanish); Cobalamina (Spanish)
Family or group: One of the B vitamins. MedlinePlus says it is water-soluble: it dissolves in water, and leftover amounts leave the body in the urine. The liver stores a few years' worth.
Look-alikes and adulterants: Name: Folate (vitamin B9) and folic acid; Note: Works with B12 in the body, and folic acid can hide low B12. It has its own page.; Name: Vitamin B6; Note: Often sold in the same B-complex pills; its own page covers its different cautions.
Sustainability and conservation: Not assessed.

What is inside, and how it may work

What it contains and how those compounds act in cells and animals. Laboratory and animal mechanisms are not proven effects in people.

Main compounds

Compound	Family	Where it is concentrated	Activity studied	Level of evidence
Cyanocobalamin	B12 form	Not read from a source.	Listed by MedlinePlus as an alternative name for B12. The NHS says that, for injections in the UK, hydroxocobalamin is preferred over cyanocobalamin because it stays in the body longer. ^{22 26}	Human data
Hydroxocobalamin	B12 form	Not read from a source.	The form the NHS uses for B12 injections, given by a nurse or doctor. It is a prescription treatment. ²⁶	Human data
Methylcobalamin (mecobalamin)	B12 form	Not read from a source.	Sold as a supplement and used in trials for nerve damage (15 trials, mostly at high risk of bias). No head-to-head trial against other forms was read, so it is not shown to work better. ¹⁸	Human data

Mechanisms, receptors and pathways

Target or pathway	Gene or receptor	What was found	Level
Red blood cell formation	Not applicable	MedlinePlus and the NHS say B12 helps form red blood cells. Without enough, the body makes abnormally large red blood cells that cannot work properly (megaloblastic anaemia). ^{22 25 24}	Human data
Nervous system upkeep	Not applicable	MedlinePlus and the NHS say B12 helps maintain the nervous system; deficiency can cause numbness, tingling and balance problems. ^{22 25}	Human data
Using folate	Not applicable	The NHS says B12 helps the body use folate. High-dose folic acid can hide B12 deficiency. ^{23 26}	Human data
Homocysteine lowering	Not applicable	The Cochrane heart review describes vitamins B6, B9 and B12 as homocysteine-lowering interventions. Lowering homocysteine did not change heart attack or death in 15 trials. ¹³	Human data

Absorption, metabolism and elimination

Absorption: The NHS says B12 combines with a stomach protein called intrinsic factor and is then absorbed in the last part of the small intestine (distal ileum). In pernicious anaemia the immune system attacks the cells that make intrinsic factor, so food B12 cannot be absorbed. Stomach surgery, Crohn disease and some medicines can also lower absorption. MedlinePlus says the B12 added to foods is very easy to absorb.
Distribution: MedlinePlus says the liver stores a few years' worth. The NHS says stores last around 2 to 5 years, so problems can take a long time to appear after a change in diet.
Metabolism: Not covered in the sources read.
Elimination: MedlinePlus says leftover amounts leave the body in the urine.
Bioavailability: Cochrane 2018 (low certainty): oral 1000 mcg a day gave blood B12 similar to injections over 3 to 4 months. Forms were not compared head to head in a source read. The NHS says hydroxocobalamin stays in the body longer than cyanocobalamin.

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Isolated compounds versus whole extracts

Food B12 and supplement B12 are not the same thing. Foods that contain B12 also bring other nutrients; a pill brings only what is on its label. MedlinePlus says the B12 added to fortified foods is very easy for the body to absorb. Food versus pill absorption was not compared in any source read.

Nutritional composition

B12 content of foods is from USDA FoodData Central SR Legacy (April 2018 release), read 2026-10-26 from a saved local copy; values are per 100 g and per household portion, see the Food sources item and the study table. Cooked weights and brands vary. Official intake figures (MedlinePlus: 2.4 mcg for adults; NHS: about 1.5 mcg for adults 19 to 64) differ between countries and are intake targets, not advice.

13benefits and uses looked at

28studies and sources checked

High certaintybest evidence rating found

4lab markers tracked in trials

2 high certainty1 mixed findings7 low certainty1 very low certainty1 not enough evidence1 evidence against

What was looked at

The 13 benefits and uses checked for Vitamin B12, each with how strong the evidence is. Tap one to open it.

Essential nutrient and deficiencyHigh certainty
Food sources of vitamin B12High certainty
Low B12 on vegetarian and vegan dietsLow certainty
Low B12 with metformin and acid-reducing medicinesLow certainty
Treating B12 deficiency: tablets versus injectionsLow certainty
Thinking and memoryLow certainty
DepressionEvidence against
Tiredness and energyNot enough evidence
Heart attack and strokeMixed findings
Nerve damage (neuropathy)Low certainty
Bone health and fracturesLow certainty
Pregnancy and baby outcomesVery low certainty
Anaemia in older people with slightly low B12Low certainty

Lab markers tracked in the studies

Blood vitamin B12Rate of B12 deficiencyMemory test score (MMSE)Haemoglobin in older people

What is Vitamin B12 good for?

The main studied uses and how strong the human evidence is for each. Most useful findings are about deficiency; results for people who are not deficient are mostly weak or null.

Essential nutrient and deficiencyHigh certaintyB12 helps make red blood cells, keeps nerves healthy and helps the body use folate. The liver stores a few years' worth, so a shortage builds slowly. A shortage can cause anaemia, numbness and tingling, tiredness and memory problems, and some nerve damage can become permanent. Food sources of vitamin B12High certaintyBy USDA data, 3 oz of cooked clams has about 84 mcg and braised beef liver about 60 mcg. Trout, salmon, beef and tuna have about 2 to 3.5 mcg in 3 oz; a cup of milk or a tub of plain yogurt about 1.3 mcg; an egg about 0.6 mcg. Unfortified plant foods have none. Low B12 on vegetarian and vegan dietsLow certaintyReviews find lower B12 intake and blood levels on plant-based diets, lowest in vegans. In children, the gap was clear for vegan and macrobiotic diets and disappeared once total B12 intake was counted. One adult review was written by employees of a fortified-food company. Low B12 with metformin and acid reducersLow certaintyB12 deficiency was found in 23% of people with type 2 diabetes on metformin versus 17% off it (odds ratio 2.95). Acid-reducing medicines (PPIs) showed a smaller, less certain link (odds ratio 1.42). Tablets or injections for deficiencyLow certaintyA 2018 Cochrane review of 3 small trials (153 people) found high-dose tablets raised blood B12 about as much as injections, with low certainty. No trial measured symptoms. A doctor chooses the treatment. Thinking and memoryLow certaintyIn 16 trials in people who were not clearly deficient, B12 did not improve thinking or memory. A review of B-vitamin combinations found a tiny slower fall on a 30-point memory test (0.14 points). DepressionEvidence againstNo overall effect of B12 on depression scores in a review of 16 trials, and no reliable effect in a one-month trial of 478 young adults. Tiredness and energyNot enough evidenceTiredness is a deficiency sign, but only one trial tested B12 for unexplained tiredness in people who were not deficient, so nothing can be concluded. Heart attack and strokeMixed findingsIn 15 trials of B6, folate and B12 (mostly combined), there was no change in heart attacks or deaths and a small drop in stroke (risk ratio 0.90). Nerve damage (neuropathy)Low certaintyIn 15 mostly high-risk-of-bias trials, methylcobalamin helped some measures when combined with other treatment, but not pain or symptom scores. Bone health and fracturesLow certaintyFour trials of folate, B6 and B12 together found no lower fracture risk and no better bone turnover markers. Pregnancy and baby outcomesVery low certaintyOral B12 in pregnancy may lower maternal deficiency and raise B12 in mothers and babies, but the evidence is very uncertain and effects on birth outcomes are unclear. Anaemia in older people with slightly low B12Low certaintyThree trials (210 people) found B12 pills did not change haemoglobin in older people with slightly low B12. This is separate from true B12 deficiency anaemia.

Benefits, one by one

Each card is a research question, not a promise. Tap a goal to filter. Open a card to see the studies, doses and limits.

Essential nutrient and deficiency

High certainty

Vitamin B12 helps the body make red blood cells, keep nerves healthy, use folate and handle protein. The body stores a few years' worth in the liver, so a shortage can take years to show. A shortage can cause anaemia, numbness and tingling, balance problems, tiredness and memory problems. Some nerve damage can become permanent if it is not treated.

4 studiesB12 from food and from supplements. Official intake figures are descr…

Studies, doses and limits

What the trials found

MedlinePlus says B12 is important for protein metabolism and helps form red blood cells and maintain the nervous system, and that the liver stores a few years' worth. The NHS lists symptoms of deficiency: extreme tiredness, pins and needles, a sore red tongue, mouth ulcers, muscle weakness, vision problems, mood changes from mild depression or anxiety to confusion and dementia, and problems with memory and judgement. The NHS says some of these can happen without anaemia, and that some problems, such as nervous system damage, can be irreversible. The NHS says deficiency affects around 1 in 10 people aged 75 or over and 1 in 20 people aged 65 to 74. No trial of B12 in people who are not short of it was used for this item.

Results

B12 is essential and a shortage causes real harm. Pills are expected to help mainly people who are short of B12. If you think you may be short, ask a doctor: it is diagnosed from your symptoms and a blood test.

Effect sizes as reported

No effect sizes apply: these are nutrient roles and deficiency signs, not trial results.

Why this rating

High that B12 is essential and that deficiency has recognised signs (MedlinePlus and NHS). This is not a trial result for any supplement.

Form and dose studied

B12 from food and from supplements. Official intake figures are described on the Safety tab as regulator statements only.

Who was studied

Everyone needs B12. People most often low: over 50, vegetarian or vegan without fortified foods or supplements, stomach or gut surgery, coeliac or Crohn disease, pernicious anaemia (MedlinePlus and NHS).

Limits

Role and symptom statements come from health pages, not from trials. The deficiency rates are the NHS's figures for the UK and may differ elsewhere.

Why researchers looked

People want to know whether they get enough B12, what low B12 feels like, and who is most likely to run short.

Traditional use

Vitamin B12 is an essential vitamin. Its roles in the body are well established; that is different from showing that extra B12 pills treat a condition.

Proposed mechanism Established physiology

B12 takes part in making red blood cells, in protein handling and in using folate (MedlinePlus and NHS). This is established physiology.

A proposed mechanism does not show that the effect happens in people.

Do not guess at low B12: the symptoms have many causes. See the Safety tab.

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Food sources of vitamin B12

High certainty

B12 comes naturally from animal foods only. By USDA data, 3 oz (85 g) of cooked clams has about 84 mcg and braised beef liver about 60 mcg. A 3 oz serving of cooked trout has about 3.5 mcg, salmon about 2.4 mcg, a broiled beef patty about 2.2 mcg and canned light tuna about 2.2 mcg. A cup of 2% milk has about 1.3 mcg, an 8 oz tub of plain low-fat yogurt about 1.3 mcg and one large egg about 0.6 mcg. Unfortified plant foods such as tofu have none; some fortified cereals and yeast products do.

4 studiesFood B12 is bound to protein and must be released in the stomach. Med…

Studies, doses and limits

What the trials found

MedlinePlus says B12 is found naturally in fish, meat, poultry, eggs, milk and milk products, and is not present in plant foods unless fortified. It names organ meats such as beef liver, shellfish such as clams, fortified breakfast cereals and some nutritional yeast products. The NHS lists meat, fish, milk, cheese, eggs and some fortified breakfast cereals, and says yeast extracts and soy products can be fortified. USDA FoodData Central (SR Legacy) per portion: clams, cooked, 3 oz about 84.1 mcg; beef liver, braised, 3 oz about 60.0 mcg; rainbow trout, cooked, 3 oz about 3.5 mcg; Atlantic farmed salmon, cooked, 3 oz about 2.4 mcg; light tuna in water, drained, 3 oz about 2.2 mcg; broiled beef patty, 3 oz about 2.2 mcg; 2% milk, 1 cup about 1.3 mcg; plain low-fat yogurt, 8 oz about 1.3 mcg; Swiss cheese, 1 oz about 0.9 mcg; one large hard-boiled egg about 0.6 mcg; cheddar, 1 oz about 0.3 mcg; roasted chicken breast, 3 oz about 0.3 mcg; firm tofu 0. Fortified cereals vary a lot in the USDA file, from none to about 3 mcg in a single serving, so the label matters.

Results

Animal foods supply B12 and shellfish and liver are by far the richest. Unfortified plant foods do not. These are measured amounts, not advice.

Effect sizes as reported

No effect sizes apply: these are food composition values.

Why this rating

High: these are measured food values from a national database and are consistent with MedlinePlus and NHS. Not a trial result.

Form and dose studied

Food B12 is bound to protein and must be released in the stomach. MedlinePlus says the B12 added to foods is very easy for the body to absorb.

Who was studied

People who eat no animal foods rely on fortified foods or supplements (MedlinePlus, NHS).

Limits

SR Legacy is a 2018 release; brands and fortification change. Portion values are calculated from the database's per-100 g figures. Nutritional yeast was not found in the file read.

Why researchers looked

B12 is missing from unfortified plant foods, so people want to know where it comes from.

Traditional use

Vitamin B12 is an essential vitamin. Its roles in the body are well established; that is different from showing that extra B12 pills treat a condition.

Proposed mechanism Nutrient database

Not a mechanism claim. Nutrient content is a measured fact about each food.

A proposed mechanism does not show that the effect happens in people.

Liver is very rich in B12. The NHS B vitamin pages say to avoid liver if you are pregnant; ask a doctor or midwife about it.

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Low B12 on vegetarian and vegan diets

Low certainty

Reviews of many studies find that people on plant-based diets tend to have lower B12 intake and lower B12 in the blood than meat-eaters, and vegans the lowest. In children and teens, the difference was clear for vegan and macrobiotic diets, and it disappeared when total B12 intake (food plus any supplement) was counted. The NHS says a vegan diet without fortified foods or supplements is a recognised cause of deficiency.

5 studiesFortified foods and supplements. The reviews do not compare forms.

Studies, doses and limits

What the trials found

A 2021 systematic review of 141 studies (adults) found B12 intake and status generally lower on plant-based diets, with vegans lowest on intake; its two authors work for Unilever, a company that sells fortified foods and supplements. A 2023 meta-analysis in healthy children and teens aged 5 to 18 found blood B12 lower by 97 pmol/L (95% CI -187 to -7; very large differences between studies) on plant-based diets; not significant for vegetarian diets, significant for vegan or macrobiotic diets, and the gap was cancelled out once total B12 intake was taken into account. A 2021 review says deficiency in early childhood often happens in exclusively breast-fed infants of deficient mothers.

Results

Strong, consistent link between eating no animal foods and lower B12 unless the gap is filled by fortified foods or supplements. The research shows who is at risk; it is not a trial of a treatment.

Effect sizes as reported

Children and teens: mean difference -97 pmol/L (95% CI -187 to -7), I2 98.5%. Adults: no pooled B12 numbers in the abstract.

Why this rating

Low by the study design (observational, very different results between studies, one review by authors linked to a company that sells fortified products). The underlying fact that unfortified plant foods contain no B12 is established.

Form and dose studied

Fortified foods and supplements. The reviews do not compare forms.

Who was studied

Adults and children on vegetarian, vegan or macrobiotic diets; breastfed infants of mothers on such diets.

Limits

Observational data. Deficiency was not always measured the same way. The abstracts give few B12 numbers for adults.

Why researchers looked

B12 occurs naturally only in animal foods, so people who eat few or none of them are a natural group to study.

Traditional use

Vitamin B12 is an essential vitamin. Its roles in the body are well established; that is different from showing that extra B12 pills treat a condition.

Proposed mechanism Established nutrition

Plant foods do not naturally contain B12 (MedlinePlus), so intake falls unless fortified foods or supplements are used. This is nutrition, not a hypothesis.

A proposed mechanism does not show that the effect happens in people.

Infants and pregnant or breastfeeding women on vegan diets are the groups where doctors take the most care; see the Safety tab.

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Low B12 with metformin and acid-reducing medicines

Low certainty

The NHS lists metformin (a diabetes medicine), proton pump inhibitors (acid reducers) and nitrous oxide among medicines that can lower B12. A 2022 review of 17 studies found B12 deficiency in 23% of people with type 2 diabetes on metformin and 17% of those not on it, with more deficiency at longer use and higher metformin amounts. A 2023 review of 25 studies found a smaller link for acid reducers, with results that varied.

3 studiesNot studied here: these are medicines, not B12 products.

Studies, doses and limits

What the trials found

The NHS says proton pump inhibitors (PPIs), metformin and nitrous oxide can lower B12 and that a GP will monitor if needed. A 2022 meta-analysis of 17 studies (13 cross-sectional) in people with type 2 diabetes: deficiency 23.16% on metformin versus 17.4% off it, odds ratio 2.95 (95% CI 2.18 to 4.00); longer use and higher amounts of metformin were linked to more deficiency. A 2023 meta-analysis of 25 studies (2,852 PPI users, 28,070 non-users): odds ratio 1.42 (95% CI 1.16 to 1.73). Most studies found no difference in average blood B12 between users and non-users, results varied (I2 54%), and the authors say the link is not clear. The metformin authors suggest supplemental B12 may be useful for people on metformin; this is their view, not a trial result.

Results

A real, consistent link for metformin. A weak and uncertain link for acid reducers. Neither shows that B12 pills are needed by everyone on these medicines.

Effect sizes as reported

Metformin: OR 2.95 (2.18 to 4.00). Acid reducers: OR 1.42 (1.16 to 1.73).

Why this rating

Low: observational studies (mostly cross-sectional) and, for acid reducers, high differences between studies; the PPI authors call the link unclear.

Form and dose studied

Not studied here: these are medicines, not B12 products.

Who was studied

Adults with type 2 diabetes on metformin; adults using PPIs.

Limits

Cross-sectional data show a link, not cause. Study numbers for the metformin analysis were not given in the abstract.

Why researchers looked

These are very common medicines, and B12 needs stomach acid and healthy gut absorption.

Traditional use

Vitamin B12 is an essential vitamin. Its roles in the body are well established; that is different from showing that extra B12 pills treat a condition.

Proposed mechanism Hypothesis

Not established in the sources read. The NHS says these medicines can reduce how much B12 the body has; it does not explain how.

A proposed mechanism does not show that the effect happens in people.

Never stop a prescribed medicine on your own. Ask your doctor or pharmacist about B12 checks.

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Treating B12 deficiency: tablets versus injections

Low certainty

Deficiency is treated by a doctor with injections or tablets. In the UK the NHS says it is usually injections at first, then tablets or repeat injections depending on the cause, and that hydroxocobalamin is preferred over cyanocobalamin for injections because it stays in the body longer. A 2018 Cochrane review of 3 small trials (153 people) found, with low certainty, that high-dose tablets raised blood B12 about as much as injections over 3 to 4 months.

3 studiesCochrane compared oral with intramuscular B12 (form not named in the …

Studies, doses and limits

What the trials found

NHS: most cases are treated with injections of hydroxocobalamin every other day at first; after that, a diet-related deficiency may be treated with daily tablets between meals or two injections a year, while a deficiency not related to diet usually needs an injection every 2 to 3 months for life. People with nerve symptoms are referred to a haematologist. Cochrane 2018: 3 randomised trials, 153 adults with B12 deficiency, 3 to 4 months. In two trials of oral 1000 mcg a day, blood B12 was not clinically different from injections; in one trial of oral 2000 mcg a day, blood B12 was higher by 680 pg/mL (95% CI 392.7 to 967.3) with tablets. Quality was low; adverse events were very low-quality evidence (no treatment-related events in one trial; 2 of 30 people in the oral group left early because of side effects in another). Tablets cost less in one trial. No trial reported symptoms or quality of life.

Results

Tablets and injections both raise blood B12, but the trials are small and did not measure whether people felt or functioned better. Treatment must be chosen and checked by a doctor.

Effect sizes as reported

Blood B12: no clinically relevant difference at oral 1000 mcg a day; mean difference 680 pg/mL favouring oral at 2000 mcg a day (95% CI 392.7 to 967.3).

Why this rating

Low (Cochrane GRADE) because of very few small trials; no symptom outcomes.

Form and dose studied

Cochrane compared oral with intramuscular B12 (form not named in the abstract). NHS: hydroxocobalamin injections preferred in the UK. Amounts here are trial amounts, not advice.

Who was studied

Adults aged about 39 to 72 with diagnosed B12 deficiency.

Limits

Only 3 trials (74 oral, 79 injection); only one had low or unclear risk of bias throughout. Follow-up was 3 to 4 months.

Why researchers looked

Many people with low B12 have trouble absorbing it, so doctors ask whether tablets work as well as injections.

Traditional use

Vitamin B12 is an essential vitamin. Its roles in the body are well established; that is different from showing that extra B12 pills treat a condition.

Proposed mechanism Authoritative guidance

Pernicious anaemia and some gut conditions stop B12 absorbing in the normal way (NHS). How high-dose tablets get around this is not explained in the sources read.

A proposed mechanism does not show that the effect happens in people.

Rare allergic reactions to injections are described on the Safety tab.

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Thinking and memory

Low certainty

In people who are not clearly deficient, 16 trials found no sign that B12 (alone or with folic acid and B6) improves thinking or memory. A separate review of B vitamin combinations found a very small slower fall on a memory test score (0.14 points). Older reviews of B12 in dementia found the evidence insufficient. Low B12 can cause memory problems, so this is about people who are not low.

3 studiesB12 alone, or B12 with folic acid and B6. Forms are not compared.

Studies, doses and limits

What the trials found

Markun 2021: 16 randomised trials, 6,276 people without advanced neurological disease or overt B12 deficiency; no effect of B12 alone or B complex on any area of cognitive function. Wang 2022: 95 studies (25 trials); B vitamin supplements (mostly combinations) were linked to a 0.14-point slower decline in MMSE score (95% CI 0.04 to 0.23; 6,155 people), mainly in trials longer than 12 months and in people without dementia; higher dietary folate, but not B12 or B6 intake, went with lower dementia risk. Cochrane 2003: two trials in people with dementia and low blood B12 found no significant effect; evidence insufficient.

Results

No good evidence that extra B12 sharpens memory or protects against dementia in people who are not low. Treating confirmed deficiency is a different matter and is done by a doctor.

Effect sizes as reported

MMSE (B vitamin combinations) mean difference 0.14 points (95% CI 0.04 to 0.23). B12 alone: no effect found.

Why this rating

Low: the larger review of B12 trials is null, the review with a small benefit mixes several vitamins, and the Cochrane review is old and small.

Form and dose studied

B12 alone, or B12 with folic acid and B6. Forms are not compared.

Who was studied

Older adults without advanced neurological disease or clear B12 deficiency; some trials in dementia.

Limits

A 0.14-point change on a 30-point test is tiny. People with clear deficiency were excluded from the larger review, so it cannot say what B12 does for them.

Why researchers looked

B12 deficiency can cause memory problems and confusion, so people ask whether extra B12 protects the brain.

Traditional use

Vitamin B12 is an essential vitamin. Its roles in the body are well established; that is different from showing that extra B12 pills treat a condition.

Proposed mechanism Hypothesis

Not established. A proposed idea is that B vitamins lower homocysteine, a blood marker linked to dementia risk; the reviews did not show that this protects thinking.

A proposed mechanism does not show that the effect happens in people.

Memory change that is new or worsening needs a doctor, not a supplement.

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Depression

Evidence against

A review of 16 trials found no overall effect of B12 supplements (alone or in B-vitamin combinations) on depression scores in people without overt B12 deficiency. A small trial of 478 young adults found no reliable change with one month of high-dose B12; the effects it saw were for vitamin B6.

2 studiesB12 alone or in B-complex combinations; amounts varied (the one-month…

Studies, doses and limits

What the trials found

Markun 2021 (16 trials, 6,276 people): no overall effect of B12 or B complex on depression measures. Field 2022: 478 young adults took B6 or B12 or placebo for one month; B6 lowered self-reported anxiety, while B12 produced only trends (not reliable) in anxiety and visual tasks.

Results

No evidence that B12 treats or prevents depression in people who are not deficient.

Effect sizes as reported

No pooled numbers in the abstract.

Why this rating

The main review of randomised trials is null for depression; the smaller trial is also null for B12.

Form and dose studied

B12 alone or in B-complex combinations; amounts varied (the one-month trial used a high dose).

Who was studied

Adults without overt B12 deficiency or advanced neurological disease; young adults in the one-month trial.

Limits

Short trials; B12-deficient people were excluded from the main review.

Why researchers looked

Low B12 can bring mood changes, so people ask whether extra B12 lifts mood.

Traditional use

Vitamin B12 is an essential vitamin. Its roles in the body are well established; that is different from showing that extra B12 pills treat a condition.

Proposed mechanism Hypothesis

Not established. The one-month trial's authors link B vitamins to chemical messengers that calm nerve activity, as a hypothesis.

A proposed mechanism does not show that the effect happens in people.

Depression needs care from a doctor or mental health professional.

^{12 5}

Tiredness and energy

Not enough evidence

Extreme tiredness is a common sign of B12 deficiency, and B12 helps release energy from food. But only one trial in the main review looked at unexplained tiredness in people who were not deficient, so no conclusion could be drawn. The evidence that extra B12 gives more energy to people who are not low is insufficient.

3 studiesNot compared.

Studies, doses and limits

What the trials found

The NHS lists extreme tiredness and lack of energy as deficiency symptoms and says B12 helps release energy from food. Markun 2021 found only one trial of idiopathic (unexplained) fatigue, so no analysis was possible.

Results

Tiredness caused by low B12 is expected to improve when B12 is corrected. For people who are not low, there is no good evidence of an energy boost.

Effect sizes as reported

No effect sizes: too few trials.

Why this rating

Insufficient: one trial in non-deficient people.

Form and dose studied

Not compared.

Who was studied

People with unexplained fatigue and no overt B12 deficiency.

Limits

Tiredness has many causes; a blood test is needed to know whether B12 is one.

Why researchers looked

B12 is widely sold as an energy vitamin because deficiency causes tiredness.

Traditional use

Vitamin B12 is an essential vitamin. Its roles in the body are well established; that is different from showing that extra B12 pills treat a condition.

Proposed mechanism Established physiology

B12 is involved in releasing energy from food (NHS). That role does not mean extra B12 raises energy when levels are normal.

A proposed mechanism does not show that the effect happens in people.

Ongoing tiredness needs a doctor.

^{23 25 12}

Heart attack and stroke

Mixed findings

B12 helps lower homocysteine, a blood marker once linked to heart disease. In 15 trials with 71,422 people, giving B6, folate or B12 (mostly in combination) did not change heart attacks or deaths. It was linked to a small drop in stroke (RR 0.90). These are vitamin combinations, so the effect of B12 alone is unknown.

1 studiesB6, B9 (folate) or B12, alone or in combination. B12 alone cannot be …

Studies, doses and limits

What the trials found

Cochrane 2017: 15 randomised trials (71,422 people, follow-up 1 to 7.3 years). Heart attack RR 1.02 (95% CI 0.95 to 1.10); death from any cause RR 1.01 (0.96 to 1.06); serious adverse events RR 1.07 (1.00 to 1.14); stroke RR 0.90 (0.82 to 0.99). The authors rate the evidence high-quality and say more trials are unlikely to change the picture.

Results

No protection against heart attack or early death. A small possible reduction in stroke, from vitamin combinations. This is not a reason to take B12 for the heart.

Effect sizes as reported

Stroke RR 0.90 (0.82 to 0.99); heart attack RR 1.02; all-cause death RR 1.01.

Why this rating

Mixed: no effect for heart attack and death, a small effect for stroke. High-quality trials, but they used B6, folate and B12 together.

Form and dose studied

B6, B9 (folate) or B12, alone or in combination. B12 alone cannot be separated out.

Who was studied

People with and without existing cardiovascular disease; people with end-stage kidney disease were excluded.

Limits

Combination vitamins; the stroke result is small and borderline.

Why researchers looked

High homocysteine goes with heart disease, and B vitamins lower homocysteine.

Traditional use

Vitamin B12 is an essential vitamin. Its roles in the body are well established; that is different from showing that extra B12 pills treat a condition.

Proposed mechanism Hypothesis

B12, folate and B6 help the body clear homocysteine. The Cochrane review treats lowering homocysteine as the aim of these trials; it did not prove that the aim protects the heart.

A proposed mechanism does not show that the effect happens in people.

Heart disease treatment should not be replaced by vitamins.

¹³

Nerve damage (neuropathy)

Low certainty

Methylcobalamin (also called mecobalamin) is widely used in Asia for nerve damage from diabetes or shingles. In 15 trials with 1,707 people, more people responded with it than with comparison treatments, and nerve conduction improved when it was combined with other treatment. Pain and symptom scores did not improve. Most trials were at high risk of bias.

2 studiesMecobalamin (methylcobalamin), the form studied. Whether it works bet…

Studies, doses and limits

What the trials found

Sawangjit 2020: 15 randomised trials, 1,707 people with diabetic or herpetic neuropathy; responders RR 1.17 (95% CI 1.03 to 1.33) for mecobalamin alone and RR 1.32 (1.21 to 1.45) in combination versus active control; nerve conduction better only in combination; no improvement in pain or symptom scores; no serious side effects reported. 11 of 15 trials had high risk of bias. The authors say the evidence is not clear for mecobalamin alone.

Results

Possible help for some measures when combined with other treatment, but weak evidence and no pain relief shown. Nerve damage needs medical care.

Effect sizes as reported

Responders: RR 1.17 alone; RR 1.32 combined.

Why this rating

Low: most trials had high risk of bias, comparisons were with other active treatments, and pain did not improve.

Form and dose studied

Mecobalamin (methylcobalamin), the form studied. Whether it works better than other B12 forms was not tested.

Who was studied

People with diabetic or herpetic neuropathy; B12 deficiency was not the reason for treatment.

Limits

No placebo comparisons; mixed treatment routes.

Why researchers looked

B12 deficiency damages nerves, so doctors asked whether B12 helps other nerve damage.

Traditional use

Vitamin B12 is an essential vitamin. Its roles in the body are well established; that is different from showing that extra B12 pills treat a condition.

Proposed mechanism Hypothesis

Not established in the abstract. B12 is needed to keep nerves healthy (NHS).

A proposed mechanism does not show that the effect happens in people.

New numbness or tingling should be checked by a doctor, since low B12 is one possible cause.

^{18 25}

Bone health and fractures

Low certainty

A meta-analysis of 4 trials found no lower risk of fractures and no better bone turnover markers from folate, B6 and B12 taken together, mostly in people with vascular disease. The authors suggest looking at people with very high homocysteine.

1 studiesFolate, B6 and B12 together.

Studies, doses and limits

What the trials found

Ruan 2015: 4 randomised trials; no risk reduction for osteoporotic fracture and no positive effect on bone turnover markers with B vitamin combinations (numbers not in the abstract).

Results

No evidence of benefit for bones from B12 in the trials read.

Effect sizes as reported

No numbers in the abstract.

Why this rating

Low: only 4 trials of a vitamin combination, not B12 alone.

Form and dose studied

Folate, B6 and B12 together.

Who was studied

Mostly people with vascular disease and fairly normal homocysteine.

Limits

Did not test people with very high homocysteine or B12 deficiency.

Why researchers looked

High homocysteine has been linked to weaker bones.

Traditional use

Vitamin B12 is an essential vitamin. Its roles in the body are well established; that is different from showing that extra B12 pills treat a condition.

Proposed mechanism Hypothesis

Not established. The idea is that lowering homocysteine could help bone; the trials did not show it.

A proposed mechanism does not show that the effect happens in people.

Bone health advice should come from a doctor.

¹⁷

Pregnancy and baby outcomes

Very low certainty

In 5 trials with 984 pregnant women in lower-income countries, B12 pills may have lowered the chance of B12 deficiency in the mother and raised B12 in mothers and babies, but the evidence is very uncertain. Effects on anaemia, preterm birth and low birth weight were unclear. No trial looked at neural tube defects.

2 studiesOral B12; amounts in trials ranged widely (trial amounts, not advice).

Studies, doses and limits

What the trials found

Cochrane 2024: 5 trials (984 women; 3 trials, 609 women, in the pooled analyses), oral B12 5 to 250 mcg a day from 8 to 28 weeks of pregnancy to delivery or 3 months after. Maternal deficiency RR 0.38 (95% CI 0.28 to 0.51; very low certainty); maternal total B12 +60.89 pmol/L (40.86 to 80.92; I2 85%); anaemia RR 1.08 (0.93 to 1.26; very low); preterm birth RR 0.97 (0.55 to 1.74; low); low birth weight RR 1.50 (0.93 to 2.43; low). Babies of supplemented mothers had higher B12 (+71.89 pmol/L; 20.23 to 123.54). The NHS lists pregnancy complications and birth defects among possible complications of B12 or folate deficiency.

Results

B12 status goes up, but there is no proof that this changes birth outcomes. Anyone pregnant should be guided by their doctor or midwife.

Effect sizes as reported

Maternal deficiency RR 0.38; B12 +60.89 pmol/L; preterm RR 0.97; low birth weight RR 1.50.

Why this rating

Very low to low (Cochrane GRADE): few small trials with large differences between them.

Form and dose studied

Oral B12; amounts in trials ranged widely (trial amounts, not advice).

Who was studied

Pregnant women, India, Bangladesh, South Africa and Croatia; 26% to 51% were B12 deficient at the start.

Limits

Trials in places where deficiency was common; may not apply to well-fed women in other countries.

Why researchers looked

B12 deficiency in pregnancy can affect the baby's development, and deficiency is common in some places.

Traditional use

Vitamin B12 is an essential vitamin. Its roles in the body are well established; that is different from showing that extra B12 pills treat a condition.

Proposed mechanism Established physiology

Not shown in the trials. B12 is involved in making DNA and red blood cells (Cochrane background).

A proposed mechanism does not show that the effect happens in people.

See pregnancy notes on the Safety tab.

^{6 25}

Anaemia in older people with slightly low B12

Low certainty

Pernicious anaemia is clearly tied to B12 deficiency. But a systematic review found the link between mildly low B12 and anaemia in older people inconsistent, and 3 trials (210 people) found B12 pills did not change haemoglobin in older people with slightly low B12.

2 studiesNot compared.

Studies, doses and limits

What the trials found

den Elzen 2010: 25 studies. 21 cross-sectional studies (16,185 people) were inconsistent; one longitudinal study (423 people) found no link between low B12 and later anaemia; 3 placebo-controlled trials (210 people) found no effect of B12 supplements on haemoglobin in people with slightly low B12.

Results

Slightly low B12 in older people does not clearly cause anaemia, and pills did not raise haemoglobin in those trials. True B12 deficiency anaemia is a separate, treatable condition.

Effect sizes as reported

No pooled numbers.

Why this rating

Low: results were not pooled because of large differences between studies; only 3 small trials.

Form and dose studied

Not compared.

Who was studied

Older adults with B12 concentrations below normal but not clearly deficient.

Limits

Published in 2010. Does not cover people with proven deficiency.

Why researchers looked

Low B12 is common in older people, and anaemia is too.

Traditional use

Vitamin B12 is an essential vitamin. Its roles in the body are well established; that is different from showing that extra B12 pills treat a condition.

Proposed mechanism Established physiology

B12 is needed to make red blood cells (MedlinePlus and NHS). Mildly low levels may not be enough to cause anaemia.

A proposed mechanism does not show that the effect happens in people.

Anaemia needs a doctor's diagnosis.

^{21 25}

Connections to the rest of health

How Vitamin B12 connects to the rest of our health knowledge graph. Every link says what kind of connection it is. A safety link (for example to the liver) is a warning, not a benefit. A study that merely mentions a topic never creates a benefit link.

Explore every connection: goals, body systems, organs, symptoms, genes

Kind of connection Connected to Search

A. Wellness goals

Connected to	Evidence status	Context	Studies
Balanced Nutrition	High certainty	Essential nutrient and deficiency: Vitamin B12 helps the body make red blood cells, keep nerves healthy, use folate and handle protein. The body stores a few years' worth in the liver, so a shortage can take years to show. A shortage can cause anaemia, numbness and tingling, balance problems, tiredness and memory problems. Some nerve damage can become permanent if it is not treated.	^{22 23 25 24}
Reduce Fatigue	High certainty	Essential nutrient and deficiency: Vitamin B12 helps the body make red blood cells, keep nerves healthy, use folate and handle protein. The body stores a few years' worth in the liver, so a shortage can take years to show. A shortage can cause anaemia, numbness and tingling, balance problems, tiredness and memory problems. Some nerve damage can become permanent if it is not treated.	^{22 23 25 24}
Balanced Nutrition	High certainty	Food sources of vitamin B12: B12 comes naturally from animal foods only. By USDA data, 3 oz (85 g) of cooked clams has about 84 mcg and braised beef liver about 60 mcg. A 3 oz serving of cooked trout has about 3.5 mcg, salmon about 2.4 mcg, a broiled beef patty about 2.2 mcg and canned light tuna about 2.2 mcg. A cup of 2% milk has about 1.3 mcg, an 8 oz tub of plain low-fat yogurt about 1.3 mcg and one large egg about 0.6 mcg. Unfortified plant foods such as tofu have none; some fortified cereals and yeast products do.	^{28 22 23 26}
Balanced Nutrition	Low certainty	Low B12 on vegetarian and vegan diets: Reviews of many studies find that people on plant-based diets tend to have lower B12 intake and lower B12 in the blood than meat-eaters, and vegans the lowest. In children and teens, the difference was clear for vegan and macrobiotic diets, and it disappeared when total B12 intake (food plus any supplement) was counted. The NHS says a vegan diet without fortified foods or supplements is a recognised cause of deficiency.	^{15 8 7 22 24}
Preventive Wellness	Low certainty	Low B12 on vegetarian and vegan diets: Reviews of many studies find that people on plant-based diets tend to have lower B12 intake and lower B12 in the blood than meat-eaters, and vegans the lowest. In children and teens, the difference was clear for vegan and macrobiotic diets, and it disappeared when total B12 intake (food plus any supplement) was counted. The NHS says a vegan diet without fortified foods or supplements is a recognised cause of deficiency.	^{15 8 7 22 24}
Preventive Wellness	Low certainty	Low B12 with metformin and acid-reducing medicines: The NHS lists metformin (a diabetes medicine), proton pump inhibitors (acid reducers) and nitrous oxide among medicines that can lower B12. A 2022 review of 17 studies found B12 deficiency in 23% of people with type 2 diabetes on metformin and 17% of those not on it, with more deficiency at longer use and higher metformin amounts. A 2023 review of 25 studies found a smaller link for acid reducers, with results that varied.	^{9 3 24}
Blood Sugar Balance	Low certainty	Low B12 with metformin and acid-reducing medicines: The NHS lists metformin (a diabetes medicine), proton pump inhibitors (acid reducers) and nitrous oxide among medicines that can lower B12. A 2022 review of 17 studies found B12 deficiency in 23% of people with type 2 diabetes on metformin and 17% of those not on it, with more deficiency at longer use and higher metformin amounts. A 2023 review of 25 studies found a smaller link for acid reducers, with results that varied.	^{9 3 24}
Balanced Nutrition	Low certainty	Treating B12 deficiency: tablets versus injections: Deficiency is treated by a doctor with injections or tablets. In the UK the NHS says it is usually injections at first, then tablets or repeat injections depending on the cause, and that hydroxocobalamin is preferred over cyanocobalamin for injections because it stays in the body longer. A 2018 Cochrane review of 3 small trials (153 people) found, with low certainty, that high-dose tablets raised blood B12 about as much as injections over 3 to 4 months.	^{19 26 25}
Brain Health	Low certainty	Thinking and memory: In people who are not clearly deficient, 16 trials found no sign that B12 (alone or with folic acid and B6) improves thinking or memory. A separate review of B vitamin combinations found a very small slower fall on a memory test score (0.14 points). Older reviews of B12 in dementia found the evidence insufficient. Low B12 can cause memory problems, so this is about people who are not low.	^{12 20 11}
Memory Support	Low certainty	Thinking and memory: In people who are not clearly deficient, 16 trials found no sign that B12 (alone or with folic acid and B6) improves thinking or memory. A separate review of B vitamin combinations found a very small slower fall on a memory test score (0.14 points). Older reviews of B12 in dementia found the evidence insufficient. Low B12 can cause memory problems, so this is about people who are not low.	^{12 20 11}
Mood Balance	Evidence against	Depression: A review of 16 trials found no overall effect of B12 supplements (alone or in B-vitamin combinations) on depression scores in people without overt B12 deficiency. A small trial of 478 young adults found no reliable change with one month of high-dose B12; the effects it saw were for vitamin B6.	^{12 5}
Reduce Fatigue	Not enough evidence	Tiredness and energy: Extreme tiredness is a common sign of B12 deficiency, and B12 helps release energy from food. But only one trial in the main review looked at unexplained tiredness in people who were not deficient, so no conclusion could be drawn. The evidence that extra B12 gives more energy to people who are not low is insufficient.	^{23 25 12}
Energy Boost	Not enough evidence	Tiredness and energy: Extreme tiredness is a common sign of B12 deficiency, and B12 helps release energy from food. But only one trial in the main review looked at unexplained tiredness in people who were not deficient, so no conclusion could be drawn. The evidence that extra B12 gives more energy to people who are not low is insufficient.	^{23 25 12}
Heart Health	Mixed findings	Heart attack and stroke: B12 helps lower homocysteine, a blood marker once linked to heart disease. In 15 trials with 71,422 people, giving B6, folate or B12 (mostly in combination) did not change heart attacks or deaths. It was linked to a small drop in stroke (RR 0.90). These are vitamin combinations, so the effect of B12 alone is unknown.	¹³
Healthy Aging	Low certainty	Nerve damage (neuropathy): Methylcobalamin (also called mecobalamin) is widely used in Asia for nerve damage from diabetes or shingles. In 15 trials with 1,707 people, more people responded with it than with comparison treatments, and nerve conduction improved when it was combined with other treatment. Pain and symptom scores did not improve. Most trials were at high risk of bias.	^{18 25}
Bone Health	Low certainty	Bone health and fractures: A meta-analysis of 4 trials found no lower risk of fractures and no better bone turnover markers from folate, B6 and B12 taken together, mostly in people with vascular disease. The authors suggest looking at people with very high homocysteine.	¹⁷
Pregnancy Support	Very low certainty	Pregnancy and baby outcomes: In 5 trials with 984 pregnant women in lower-income countries, B12 pills may have lowered the chance of B12 deficiency in the mother and raised B12 in mothers and babies, but the evidence is very uncertain. Effects on anaemia, preterm birth and low birth weight were unclear. No trial looked at neural tube defects.	^{6 25}
Womens Wellness	Very low certainty	Pregnancy and baby outcomes: In 5 trials with 984 pregnant women in lower-income countries, B12 pills may have lowered the chance of B12 deficiency in the mother and raised B12 in mothers and babies, but the evidence is very uncertain. Effects on anaemia, preterm birth and low birth weight were unclear. No trial looked at neural tube defects.	^{6 25}
Healthy Aging	Low certainty	Anaemia in older people with slightly low B12: Pernicious anaemia is clearly tied to B12 deficiency. But a systematic review found the link between mildly low B12 and anaemia in older people inconsistent, and 3 trials (210 people) found B12 pills did not change haemoglobin in older people with slightly low B12.	^{21 25}

B. Body systems

Connected to	Kind of connection	Evidence status	Context	Studies
Nervous System	Biological association	High certainty	Studied for: Essential nutrient and deficiency Studied for: Treating B12 deficiency: tablets versus injections	^{22 23 25 24 19 26 12 20 11 5 18}
Blood	Biological association	High certainty	Studied for: Essential nutrient and deficiency Studied for: Low B12 on vegetarian and vegan diets	^{22 23 25 24 15 8 7 9 3 19 26 6 21}
Nutrition	Biological association	High certainty	Studied for: Essential nutrient and deficiency Studied for: Food sources of vitamin B12	^{22 23 25 24 28 26 15 8 7 9 3}
Digestive System	Biological association	High certainty	Studied for: Food sources of vitamin B12 Studied for: Low B12 with metformin and acid-reducing medicines	^{28 22 23 26 9 3 24}
Brain Focus	Biological association	Low certainty	Studied for: Thinking and memory	^{12 20 11}
Stress Mood	Biological association	Evidence against	Studied for: Depression	^{12 5}
Energy Fatigue	Biological association	Not enough evidence	Studied for: Tiredness and energy	^{23 25 12}
Cardiovascular System	Biological association	Mixed findings	Studied for: Heart attack and stroke	¹³
Musculoskeletal System	Biological association	Low certainty	Studied for: Bone health and fractures	¹⁷
Reproductive System	Biological association	Very low certainty	Studied for: Pregnancy and baby outcomes	^{6 25}

I. Biomarkers

Connected to	Kind of connection	Evidence status	Context	Studies
Blood vitamin B12	Biological association	Low certainty	Measured in trials: higher. A lab change is not the same as a health benefit.	^{19 6}
Rate of B12 deficiency	Biological association	Low certainty	Measured in trials: mixed. A lab change is not the same as a health benefit.	^{9 3 6}
Memory test score (MMSE)	Biological association	Low certainty	Measured in trials: higher (slower decline), very small. A lab change is not the same as a health benefit.	²⁰
Haemoglobin in older people	Biological association	Low certainty	Measured in trials: no change. A lab change is not the same as a health benefit.	²¹

K. Biological pathways

Connected to	Kind of connection	Evidence status	Context	Studies
Folate (vitamin B9)	Preliminary mechanism	Human	B12 helps the body use folate; folic acid can hide low B12.	^{23 14}

L. Active compounds

Connected to	Kind of connection	Evidence status	Context	Studies
Cyanocobalamin	Biological association	Human	Listed by MedlinePlus as an alternative name for B12. The NHS says that, for injections in the UK, hydroxocobalamin is preferred over cyanocobalamin because it stays in the body longer.	^{22 26}
Hydroxocobalamin	Biological association	Human	The form the NHS uses for B12 injections, given by a nurse or doctor. It is a prescription treatment.	²⁶
Methylcobalamin (mecobalamin)	Biological association	Human	Sold as a supplement and used in trials for nerve damage (15 trials, mostly at high risk of bias). No head-to-head trial against other forms was read, so it is not shown to work better.	¹⁸

Each connection is stored with the ingredient, the connected record, the kind of connection, the evidence status, the supporting studies, the preparation or compound involved, and a review date (last reviewed October 26, 2026).

Evidence at a glance: what changed in 1 lab markers

Tap a number to show only those markers. Counts are markers, not people.

Other1

The evidence

The research centre for Vitamin B12. Every record here was checked against PubMed or the publisher's page; we never list a study we have not verified.

Evidence by outcome

Essential nutrient and deficiency 4 studies High certainty Food sources of vitamin B12 4 studies High certainty Low B12 on vegetarian and vegan diets 5 studies Low certainty Low B12 with metformin and acid-reducing medicines 3 studies Low certainty Treating B12 deficiency: tablets versus injections 3 studies Low certainty Thinking and memory 3 studies Low certainty Depression 2 studies Evidence against Tiredness and energy 3 studies Not enough evidence Heart attack and stroke 1 study Mixed findings Nerve damage (neuropathy) 2 studies Low certainty Bone health and fractures 1 study Low certainty Pregnancy and baby outcomes 2 studies Very low certainty Anaemia in older people with slightly low B12 2 studies Low certainty

Bars show how many studies we found for each outcome, not how well it works. People are added up across trials only (reviews are not added, to avoid double counting).

How we rate evidence

High certainty

Several well-run trials or reviews agree; further research is unlikely to change the picture much.

Moderate certainty

Good trials point the same way, but some doubt remains.

Low certainty

Small, short or inconsistent trials. The finding could change with better research.

Very low certainty

Very little or very weak human data. Treat as a possibility only.

Mixed findings

Trials or reviews disagree with each other.

Not enough evidence

Not enough human research to say either way.

Evidence against

Good research found no benefit, or found harm.

We take the reviewers' own risk-of-bias and GRADE statements where they exist, and otherwise judge from study size, design, consistency, directness and whether a product matches what is sold. Many publications do not make evidence high. Method note: We started from our existing vitamin B12 summary, read MedlinePlus and three NHS pages, re-checked food values in saved USDA FoodData Central data, and re-read PubMed abstracts for reviews, trials, cohort studies and case reports. Only abstracts were read for studies. The NIH Office of Dietary Supplements page was blocked and is marked unread.

Study library: every study we checked 28

Design Research type Year from Search

Study	Design	People	Product, dose, length	Result
Bilwani 2005 Anaphylactic reaction after intramuscular injection of cyanocobalamin (vitamin B12): a case report. J Pak Med Assoc · PMID 15960291	Case report	1 A 52-year-old woman with B12-deficiency anaemia	Cyanocobalamin by intramuscular injection Injection Not given in the abstract Single injection	A severe allergic reaction (anaphylaxis) after a B12 injection. She later took B12 by mouth with no problem. The authors call this reaction rare but serious. One case (Not applicable) Methods, limits and funding Outcomes: Allergic reaction Limitations: A single case report. Funding and conflicts: Not stated in the abstract. Read: abstract
Brasky 2017 Long-Term, Supplemental, One-Carbon Metabolism-Related Vitamin B Use in Relation to Lung Cancer Risk in the Vitamins and Lifestyle (VITAL) Cohort. J Clin Oncol · PMID 28829668 · DOI	Prospective cohort	77118 77,118 adults aged 50 to 76 in the US; 808 lung cancers over follow-up	Supplemental vitamin B6, folate and B12 (individual supplements and multivitamins) Supplements 10-year average daily amounts; the highest B12 group was above 55 mcg a day (observational exposure, not advice) 10-year average exposure · vs Non-users	Not linked to lung cancer in women. In men, B12 taken as an individual supplement (not in multivitamins) was linked to a 30% to 40% higher risk of lung cancer, and to almost double the risk at the highest 10-year average amounts. The link was stronger in men who smoked. Men, highest B12 group (above 55 mcg a day) hazard ratio 1.98 (95% CI 1.32 to 2.97) Methods, limits and funding Outcomes: Lung cancer Limitations: Observational: it cannot prove cause and effect; people who take large B12 amounts may differ in other ways. Funding and conflicts: Supported by US National Cancer Institute grants. Read: abstract
Choudhury 2023 Vitamin B12 deficiency and use of proton pump inhibitors: a systematic review and meta-analysis. Expert Rev Gastroenterol Hepatol · PMID 37060552 · DOI	Meta analysis observational	30922 25 studies: 2,852 people using acid-reducing proton pump inhibitors (PPIs) and 28,070 non-users	Proton pump inhibitor use (a medicine), not a supplement · vs Non-users of PPIs	B12 deficiency was somewhat more common among PPI users. Most studies found no difference in average blood B12 between users and non-users. The authors say the effect is small, results varied between studies, and the link is not clear. Odds ratio 1.42 for B12 deficiency in PPI users; 1.49 for PPI use among people with deficiency (95% CI 1.16 to 1.73 (I2 54%); 1.20 to 1.85 (I2 68%)) Methods, limits and funding Outcomes: Frequency of B12 deficiency; blood B12 levels Limitations: Observational studies; moderate to high differences between studies; not registered; the authors call for better long-term studies. Funding and conflicts: Not stated in the abstract. Read: abstract
Collin 2010 Circulating folate, vitamin B12, homocysteine, vitamin B12 transport proteins, and risk of prostate cancer: a case-control study, systematic review, and meta-analysis. Cancer Epidemiol Biomarkers Prev · PMID 20501771 · DOI	Case control and meta analysis	2968 1,461 men with prostate cancer and 1,507 controls (UK, ages 50 to 69), plus a meta-analysis of studies	Blood levels of B12 and related markers (not supplements) · vs Men without prostate cancer	Higher blood B12 (and a B12 transport protein) went with a higher chance of prostate cancer. The authors say further research is needed to learn whether the link is causal. Pooled odds ratio 1.10 per 100 pmol/L higher blood B12 (95% CI 1.01 to 1.19) Methods, limits and funding Outcomes: Prostate cancer risk Limitations: Blood levels, not supplement use; high levels can reflect disease or other causes, so this does not show that B12 causes cancer. Funding and conflicts: Supported by Medical Research Council and NCI grants. Read: abstract
Field 2022 High-dose Vitamin B6 supplementation reduces anxiety and strengthens visual surround suppression. Hum Psychopharmacol · PMID 35851507 · DOI	Randomized trial	478 478 young adults (anxiety measured in 265, depression in 146)	High-dose vitamin B6 or vitamin B12 (form not given in the abstract) Supplements High dose (not stated in the abstract) 1 month · vs Placebo	B6 reduced self-reported anxiety and gave a trend towards less depression. B12 produced only trends in anxiety and visual processing, with no reliable effects. B12: trends only; no numbers in the abstract (Not given in the abstract) Methods, limits and funding Outcomes: Self-reported anxiety and depression; visual and touch tests Limitations: One month; young adults; B12 results were not statistically reliable. Funding and conflicts: No conflicts of interest declared. Read: abstract
Finkelstein 2024 Vitamin B12 supplementation during pregnancy for maternal and child health outcomes. Cochrane Database Syst Rev · PMID 38189492 · DOI	Systematic review	984 5 trials in pregnant women in India, Bangladesh, South Africa and Croatia (3 trials, 609 women, in the meta-analyses)	Oral vitamin B12 Supplements 5 to 250 mcg a day across trials (trial amounts, not advice) 8 to 38 weeks · vs Placebo or no B12	B12 in pregnancy may lower the chance of maternal B12 deficiency and raise B12 levels in mothers and babies, but the evidence is very uncertain. Effects on anaemia, preterm birth and low birth weight were unclear. No trial looked at neural tube defects. Maternal deficiency RR 0.38; maternal B12 +60.89 pmol/L; preterm birth RR 0.97; low birth weight RR 1.50; anaemia RR 1.08 (Deficiency 0.28 to 0.51; B12 40.86 to 80.92; preterm 0.55 to 1.74; low birth weight 0.93 to 2.43; anaemia 0.93 to 1.26) Methods, limits and funding Outcomes: Mother and baby B12 status, anaemia, preterm birth, birth weight Limitations: Small trials in low- and middle-income countries; very low to low certainty; high differences between trials. Funding and conflicts: Authors report no conflicts relevant to the review; none were investigators on included trials. Read: abstract
Hasbaoui 2021 Vitamin B12 deficiency: case report and review of literature. Pan Afr Med J · PMID 34046142 · DOI	Case report and review	1 Infants and young children with B12 deficiency (one case report plus review)	Vitamin B12 deficiency in early childhood	The review says most cases of B12 deficiency in early childhood occur in exclusively breast-fed infants of deficient mothers, with vomiting, tiredness, poor growth, low muscle tone and lost skills appearing between 2 and 12 months. Treatment corrected the chemical markers within days. It advises vegetarian and vegan mothers to guard against B12 shortage in pregnancy and breastfeeding. One case plus narrative review (Not applicable) Methods, limits and funding Outcomes: Neurodevelopment Limitations: Case report with a narrative review; not systematic. Funding and conflicts: Authors declare no competing interests. Read: abstract
Jensen 2023 Vitamin B12 levels in children and adolescents on plant-based diets: a systematic review and meta-analysis. Nutr Rev · PMID 36413044 · DOI	Systematic review meta analysis	Healthy children and adolescents aged 5 to 18 on plant-based diets	Diet pattern (plant-based versus omnivore), not a supplement · vs Omnivorous children	Children and teens on plant-based diets had lower blood B12 than omnivores. The gap was clear for vegan and macrobiotic diets but not for vegetarian diets. When total B12 intake (diet plus any supplement) was accounted for, the gap disappeared. Mean difference -97 pmol/L (95% CI -187 to -7; I2 98.5%) Methods, limits and funding Outcomes: Blood vitamin B12 level Limitations: Very large differences between studies; observational. Funding and conflicts: Not stated in the abstract. Read: abstract
Kakarlapudi 2022 Effect of Metformin on Vitamin B12 Deficiency in Patients With Type 2 Diabetes Mellitus and Factors Associated With It: A Meta-Analysis. Cureus · PMID 36628003 · DOI	Meta analysis observational	17 studies (13 cross-sectional, 3 retrospective cohorts, 1 case-control) in people with type 2 diabetes	Metformin use (a medicine), not a supplement · vs People with type 2 diabetes not on metformin	B12 deficiency was found in 23.16% of people on metformin and 17.4% of those not on it. Longer metformin use and higher metformin amounts were linked to more deficiency. Odds ratio 2.95 for B12 deficiency with metformin (95% CI 2.18 to 4.00) Methods, limits and funding Outcomes: Rate of B12 deficiency Limitations: Mostly cross-sectional studies, so it shows a link, not cause and effect. Study numbers were not given in the abstract. Funding and conflicts: Authors declare no competing interests. Read: abstract
Kang 2015 Vitamin B12 modulates the transcriptome of the skin microbiota in acne pathogenesis. Sci Transl Med · PMID 26109103 · DOI	Small human study and lab	10 10 healthy volunteers given B12, plus skin bacteria grown in the lab and acne patients compared with healthy people	Vitamin B12 supplementation (form and amount not given in the abstract) Supplements Not given in the abstract Not given in the abstract (one person developed acne after 1 week)	B12 changed how acne-linked skin bacteria behave in people and in lab cultures. One of 10 people developed acne a week after starting B12. The authors suggest this may explain why some people break out when taking B12. 1 of 10 volunteers developed acne (Not applicable) Methods, limits and funding Outcomes: Skin bacteria activity; acne Limitations: Very small, no control group; mostly lab work. Funding and conflicts: The University of California holds a patent application on acne targets related to this work, naming several authors as inventors. Read: abstract
Malouf 2003 Vitamin B12 for cognition. Cochrane Database Syst Rev · PMID 12918012 · DOI	Systematic review	2 trials in people with dementia and low blood B12	Vitamin B12 (form and amount not given in the abstract) Supplements Not given in the abstract Not given in the abstract · vs Placebo	No statistically significant effect of B12 on thinking and memory. The authors call the evidence insufficient. No trials in people without dementia were found. No significant effect (Not given in the abstract) Methods, limits and funding Outcomes: Cognitive function Limitations: Old review (search in 2002); two small trials. Funding and conflicts: Not stated in the abstract. Read: abstract
Markun 2021 Effects of Vitamin B12 Supplementation on Cognitive Function, Depressive Symptoms, and Fatigue: A Systematic Review, Meta-Analysis, and Meta-Regression. Nutrients · PMID 33809274 · DOI	Systematic review meta analysis	6276 16 randomised trials in people without advanced neurological disease or obvious B12 deficiency	Vitamin B12 alone, or B12 with folic acid with or without B6 (B complex) Supplements Varied by trial Varied by trial · vs Placebo	No evidence that B12 alone or B complex improved any part of thinking and memory. No overall effect on depression scores. Only one trial looked at unexplained tiredness, so it could not be analysed. The authors conclude B12 is likely ineffective for thinking or mood in people without advanced neurological disease. No effect found; no pooled numbers in the abstract (Not given in the abstract) Methods, limits and funding Outcomes: Cognitive function, depressive symptoms, tiredness Limitations: People who were clearly deficient were left out, so this does not apply to them. Funding and conflicts: Authors declare no conflict of interest. Read: abstract
Marti-Carvajal 2017 Homocysteine-lowering interventions for preventing cardiovascular events. Cochrane Database Syst Rev · PMID 28816346 · DOI	Systematic review meta analysis	71422 15 randomised trials, 1 to 7.3 years of follow-up, people with and without existing cardiovascular disease	Vitamins B6, B9 (folate) or B12, alone or in combination (mostly combinations) Supplements Varied by trial 1 to 7.3 years · vs Placebo	No difference in heart attacks or deaths from any cause. A small fall in stroke. Serious adverse events were not clearly different (RR 1.07, interval just touching 1.00). The authors rate these results high-quality. Heart attack RR 1.02; death RR 1.01; stroke RR 0.90; serious adverse events RR 1.07 (Heart attack 0.95 to 1.10; death 0.96 to 1.06; stroke 0.82 to 0.99; serious adverse events 1.00 to 1.14) Methods, limits and funding Outcomes: Heart attack, stroke, death from any cause, serious adverse events Limitations: These are vitamin combinations, so the effect of B12 alone cannot be separated. Excluded people with end-stage kidney disease. Funding and conflicts: One author reported past paid teaching workshops for two drug companies, unrelated to the review. Read: abstract
Miller 2024 Excess Folic Acid and Vitamin B12 Deficiency: Clinical Implications? Food Nutr Bull · PMID 38987872 · DOI	Narrative review	Review of clinical and population studies of folic acid and B12 status	Folic acid (synthetic folate) in relation to B12 status Historic high-dose folic acid treatment was above 5 mg a day (stated in the abstract as history, not advice)	High-dose folic acid can ease the anaemia of B12 deficiency and so hide it while nerve damage continues. People with low B12 and high folate scored lower on thinking tests. The authors say the evidence is mostly correlative and the explanation is untested, but warrants vigilance in people at risk of low B12. No pooled numbers (Not applicable) Methods, limits and funding Outcomes: B12 deficiency masking and worsening Limitations: Narrative review; evidence mainly observational or uncontrolled. Funding and conflicts: One author co-holds a patent for a B12 absorption assay; another author is an editor of a nutrition journal. Read: abstract
Neufingerl 2021 Nutrient Intake and Status in Adults Consuming Plant-Based Diets Compared to Meat-Eaters: A Systematic Review. Nutrients · PMID 35010904 · DOI	Systematic review	141 studies (observational and intervention) of adults on vegetarian, vegan and meat-based diets	Diet pattern (plant-based versus meat-eating), not a supplement · vs Meat-eaters	Intake and status of vitamin B12 were generally lower in plant-based diets than in meat-eaters. Vegans had the lowest B12 intake. Every diet pattern, including meat-based, had some nutrient gaps. No pooled numbers for B12 in the abstract (Not applicable) Methods, limits and funding Outcomes: Nutrient intake and blood markers, including vitamin B12 Limitations: Mostly observational; abstract gives no B12 numbers. Funding and conflicts: Both authors are employees of Unilever, which markets fortified foods and supplements (stated in the paper). Treat as industry-linked. Read: abstract
Patel 2024 Nitrous oxide myelopathy: a case series. N Z Med J · PMID 39024584 · DOI	Case series	12 12 adults (mean age 27.5) treated in one New Zealand hospital for spinal cord and nerve damage from recreational nitrous oxide	Recreational nitrous oxide (laughing gas); some also took over-the-counter B12	Numbness, weakness and mental changes were the most common problems. Four people who used large amounts of nitrous oxide were also taking over-the-counter B12 supplements. Nine of twelve were independent at last follow-up; three needed ongoing help. 12 patients; 3 needed ongoing support (Not applicable) Methods, limits and funding Outcomes: Neurological outcome (modified Rankin Scale) Limitations: Small case series from one hospital. Funding and conflicts: Authors have no conflicts of interest to declare. Read: abstract
Ruan 2015 Effect of B vitamin (folate, B6, and B12) supplementation on osteoporotic fracture and bone turnover markers: a meta-analysis. Med Sci Monit · PMID 25805360 · DOI	Meta-analysis	4 randomised trials, mostly in people with vascular disease and fairly normal homocysteine	Folate, B6 and B12 given together Supplements Varied by trial Varied by trial · vs Placebo	No lower risk of fracture and no improvement in bone turnover markers with the B vitamin combination. No effect found; numbers not in the abstract (Not given in the abstract) Methods, limits and funding Outcomes: Osteoporotic fracture; bone turnover markers Limitations: Only 4 trials; combination of vitamins; not tested in people with very high homocysteine or no fortified foods. Funding and conflicts: Not stated in the abstract. Read: abstract
Sawangjit 2020 Efficacy and Safety of Mecobalamin on Peripheral Neuropathy: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. J Altern Complement Med · PMID 32716261 · DOI	Systematic review meta analysis	1707 15 trials in people with nerve damage from diabetes or shingles (herpetic neuropathy)	Mecobalamin (methylcobalamin), alone or combined with other treatments Supplements and injections (not specified in the abstract) Varied by trial Varied by trial · vs Active treatments	More people responded with mecobalamin alone or combined than with comparison treatments. Nerve conduction improved only when it was combined with other treatment. Neither pain scores nor symptom scores improved. No serious side effects were reported. The authors say the evidence is not clear for mecobalamin alone. Responders: alone RR 1.17; combined RR 1.32 (Alone 1.03 to 1.33; combined 1.21 to 1.45) Methods, limits and funding Outcomes: Clinical response, pain score, symptom score, nerve conduction velocity, adverse events Limitations: 11 of 15 trials were at high risk of bias; compared with active treatments rather than placebo; people were not shown to be B12-deficient. Funding and conflicts: Not stated in the abstract. Read: abstract
Wang 2018 Oral vitamin B(12) versus intramuscular vitamin B(12) for vitamin B(12) deficiency. Cochrane Database Syst Rev · PMID 29543316 · DOI	Systematic review	153 3 randomised trials in adults with vitamin B12 deficiency (mean ages 38.6 to 72)	Vitamin B12 by mouth versus by intramuscular injection (form not named in the abstract) Oral and injected Oral 1000 mcg a day in two trials and 2000 mcg a day in one trial (trial amounts, not advice) 3 to 4 months · vs Intramuscular vitamin B12	At 1000 mcg a day by mouth there was no clinically relevant difference in blood B12 compared with injections (low-certainty). At 2000 mcg a day by mouth one trial found higher blood B12 than with injections. Adverse events: very low-certainty evidence. Oral treatment cost less in one trial. No trial reported symptoms or quality of life. Blood B12: no clinically relevant difference at 1000 mcg a day oral; mean difference 680 pg/mL in favour of oral at 2000 mcg a day (95% CI 392.7 to 967.3 pg/mL (2000 mcg trial)) Methods, limits and funding Outcomes: Blood B12 level, symptoms, adverse events, cost Limitations: Only 3 small trials (74 oral, 79 injection); only one had low or unclear risk of bias throughout; no pooled analysis; no symptom outcomes. Funding and conflicts: Authors report no known conflicts of interest. Read: abstract
Wang 2022 B vitamins and prevention of cognitive decline and incident dementia: a systematic review and meta-analysis. Nutr Rev · PMID 34432056 · DOI	Systematic review meta analysis	46175 95 studies: 25 randomised trials, 20 cohort studies and 50 cross-sectional studies	B vitamins (mostly combinations including B12, B6 and folate); B12 intake in cohort studies Supplements and food intake Varied by study Varied; the benefit appeared in studies longer than 12 months · vs Placebo (trials); lower intake (cohorts)	B vitamin supplements were linked to a very small slower fall in MMSE score, mainly in longer trials and in people without dementia. In cohort studies, higher folate intake, but not higher B12 or B6 intake, was linked to a lower risk of dementia. Low B12 level was not linked to dementia risk in the cross-sectional data. MMSE mean difference 0.14 points (B vitamin combinations versus placebo) (95% CI 0.04 to 0.23 (6,155 people)) Methods, limits and funding Outcomes: Mini-Mental State Examination (MMSE) change; dementia risk Limitations: Mixes many vitamin combinations, so it cannot isolate B12; a 0.14-point change on a 30-point test is tiny. Funding and conflicts: Not stated in the abstract. Read: abstract
den Elzen 2010 Subnormal vitamin B12 concentrations and anaemia in older people: a systematic review. BMC Geriatr · PMID 20573208 · DOI	Systematic review	16185 25 studies in older people: 21 cross-sectional, 1 longitudinal, 3 randomised trials (210 people)	Vitamin B12 supplements (in the 3 trials) Supplements Varied by trial During follow-up · vs Placebo	Cross-sectional studies gave inconsistent results on whether slightly low B12 goes with anaemia in older people. In the 3 well-designed trials, B12 supplements did not change haemoglobin in people with slightly low B12. No effect on haemoglobin in the 3 trials; not pooled (Not applicable) Methods, limits and funding Outcomes: Anaemia and haemoglobin Limitations: Large differences between studies, so results were not pooled. Funding and conflicts: Not stated in the abstract. Read: abstract
s-medlineplus-b12 MedlinePlus Medical Encyclopedia: Vitamin B12 (review date 2025-01-21) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-nhs-b-vitamins NHS: Vitamins and minerals, B vitamins and folic acid (vitamin B12 section; page last reviewed 2020-08-03) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-nhs-b12-causes NHS: Vitamin B12 or folate deficiency anaemia, causes (page last reviewed 2023-02-20) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-nhs-b12-deficiency NHS: Vitamin B12 or folate deficiency anaemia, overview, symptoms and complications (page last reviewed 2023-02-20) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-nhs-b12-treatment NHS: Vitamin B12 or folate deficiency anaemia, treatment (page last reviewed 2023-02-20) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-ods-b12 NIH Office of Dietary Supplements: Vitamin B12 fact sheet for health professionals · Source	Reference database n/a			Methods, limits and funding Read: not-read
s-usda-sr-legacy-b12 USDA FoodData Central, SR Legacy (April 2018 release): vitamin B-12 content of common foods · Source	Reference database n/a			Methods, limits and funding Read: full-text

What we do not know yet

The NIH Office of Dietary Supplements fact sheet was blocked, so the US view on upper limits was not read.
No head-to-head trial of cyanocobalamin, methylcobalamin and hydroxocobalamin was read.
Most trials mix B12 with folate or B6, so the effect of B12 alone is often unknown.
No source was read on kidney disease, liver safety, cobalt allergy, or contamination and label accuracy of B12 products.
The lung and prostate cancer links come from observational studies and do not show cause.
B12 for eye health, migraine, hair, skin, sleep and sport was not researched here.

How new research is added

New studies are found by a saved PubMed search and placed in a review queue before the page changes.

Lab markers

What changed in blood or saliva tests during trials. A changed number is not the same as feeling or being healthier, and we give no "normal ranges".

Other 4

●

Blood vitamin B12

Higher in trials

The amount of B12 in the blood, usually reported in pmol/L or pg/mL.

Low certainty

Results and what it means

Why it was measured

To see whether treatment or supplements raise B12 in people who are low, including in pregnancy.

Statistical vs. clinical meaning

Blood B12 rises with supplements in people who are low. It does not by itself show better health.

Safety implication

Very high blood B12 has been linked to disease in observational studies; see the Safety tab.

Study	Result	People	Product
¹⁹	No clinically relevant difference between oral 1000 mcg a day and injections; higher with oral 2000 mcg a day (mean difference 680 pg/mL, 95% CI 392.7 to 967.3)	3 trials, 153 adults with B12 deficiency, 3 to 4 months	Oral versus injected vitamin B12
⁶	Higher total B12 in mothers (mean difference +60.89 pmol/L, 95% CI 40.86 to 80.92; I2 85%) and in babies (+71.89 pmol/L, 95% CI 20.23 to 123.54)	Pregnant women, 3 trials (412 women); 2 trials (144 children)	Oral vitamin B12 in pregnancy, 5 to 250 mcg a day

^{19 6}

↕

Rate of B12 deficiency

Mixed results in trials

The share of people whose B12 is low enough to count as deficient.

Low certainty

Results and what it means

Why it was measured

To see whether a medicine, a diet or pregnancy supplements change how often deficiency happens.

Statistical vs. clinical meaning

Medicine links are observational. The pregnancy result is from small trials and is very uncertain.

Safety implication

Talk to a doctor before assuming you are or are not low.

Study	Result	People	Product
⁹	Deficiency 23.16% with metformin versus 17.4% without (OR 2.95, 95% CI 2.18 to 4.00)	17 mostly cross-sectional studies in type 2 diabetes	Metformin use (higher rate with metformin)
³	Odds ratio 1.42 (95% CI 1.16 to 1.73) for deficiency in PPI users; most studies found no difference in average blood B12	25 studies, 2,852 PPI users, 28,070 non-users	Proton pump inhibitors (higher rate with PPIs)
⁶	Maternal deficiency 25.9% with B12 versus 67.9% without (RR 0.38, 95% CI 0.28 to 0.51)	2 trials, 272 pregnant women	Oral vitamin B12 in pregnancy (lower rate with B12)

^{9 3 6}

●

Memory test score (MMSE)

Higher (slower decline), very small in trials

The Mini-Mental State Examination is a 30-point test of memory and thinking.

Low certainty

Results and what it means

Why it was measured

To see whether B vitamins slow the fall in thinking test scores.

Statistical vs. clinical meaning

A 0.14-point change on a 30-point scale is tiny and may not matter in daily life.

Safety implication

None identified in the abstract.

Study	Result	People	Product
²⁰	Mean difference 0.14 points (95% CI 0.04 to 0.23) versus placebo	6,155 people in the randomised trials within a 95-study meta-analysis	B vitamin combinations (B12 not separated)

²⁰

●

Haemoglobin in older people

No change in trials

The oxygen-carrying protein in red blood cells; low levels mean anaemia.

Low certainty

Results and what it means

Why it was measured

To see whether B12 pills correct anaemia in older people with slightly low B12.

Statistical vs. clinical meaning

Slightly low B12 did not clearly explain anaemia in these older adults.

Safety implication

None identified.

Study	Result	People	Product
²¹	No effect of B12 supplements on haemoglobin during follow-up	3 placebo-controlled trials, 210 older people with subnormal B12	Vitamin B12 supplements (not pooled)

²¹

Safety

What studies and official sources say about side effects, medicines and who should check first. Each point shows what kind of evidence it comes from.

Main points to know 4

Low B12 can damage nerves for good if it is missed. The NHS says some problems caused by B12 deficiency, such as damage to the nervous system, can be irreversible, so it should be diagnosed and treated as soon as possible. Numbness or tingling, balance trouble, memory or mood change, and extreme tiredness can all have other causes. A blood test is how a doctor tells. Do not rely on guessing or on a supplement to cover symptoms that are new or getting worse. Authoritative guidance ^{25 22}
Nitrous oxide (laughing gas) can cause B12-type nerve damage, and B12 pills may not prevent it. The NHS lists nitrous oxide among things that can lower B12. A case series from one New Zealand hospital described 12 young adults with spinal cord and nerve damage after recreational nitrous oxide use. Numbness, weakness and mental changes were the most common problems; four had also been taking over-the-counter B12 supplements. Nine were independent at the last check and three needed ongoing help. If you have used nitrous oxide and have numbness, weakness or trouble walking, see a doctor urgently. Case series and authoritative guidance ^{16 24}
Folic acid can hide low B12. The NHS says folic acid treatment can sometimes improve symptoms so much that it hides an underlying B12 deficiency, which is why a GP checks B12 before starting folic acid. A 2024 review says high-dose folic acid eased the anaemia of B12 deficiency in the past while nerve damage went on, and that people with low B12 and high folate scored lower on thinking tests; the authors say the evidence is mainly correlative, not proven. Authoritative guidance and review ^{26 14 23}
Large amounts as individual supplements and lung cancer in men (observational). In the VITAL study of 77,118 people aged 50 to 76, men who used B12 as an individual supplement (not in a multivitamin) had a 30% to 40% higher risk of lung cancer. At the highest 10-year average, above 55 mcg a day, the hazard ratio was 1.98 (95% CI 1.32 to 2.97). The risk was higher in men who smoked. No link was seen in women. This is observational: it cannot prove cause and effect, and the authors conclude only that B supplements are not protective for lung cancer and may be harmful. Prospective cohort ²

Side effects 3

Effect	How often	Severity and recovery	Evidence
Few side effects are documented at ordinary amounts Quality of the adverse event evidence was rated very low by Cochrane.	Not given. The NHS says there is not enough evidence to know what effects high daily doses of B12 supplements might have. In the Cochrane review of tablets versus injections, one trial reported no treatment-related events and in another 2 of 30 people (6.7%) in the oral group left early because of side effects.	Not described in the sources read Not described	Authoritative guidance and systematic review ^{23 19}
Acne flare-ups in some people The authors hold a patent application related to this work (acne treatment targets).	1 of 10 healthy volunteers developed acne a week after starting B12 in a small study with lab work; no rate for the general public was found.	Skin problem, not described as serious Not described in the abstract	Small human study and lab ¹⁰
Severe allergic reaction (anaphylaxis) after an injection One case report; the authors note possible sensitisation to the B12 molecule or an IgE-mediated reaction.	Described as rare; one case report of a 52-year-old woman after a cyanocobalamin injection. She later took B12 by mouth with no problem.	Can be life-threatening Not described in the abstract	Case report ¹

Liver

No liver injury from vitamin B12 was found in the sources read. A liver-safety reference (LiverTox) was not opened for this page.

How often. No frequency was found.

Monitoring. No agency monitoring advice was found.

This is a safety connection. It is not evidence that Vitamin B12 supports liver health.

Medicines and supplements 6

With	Why it matters	Importance	Evidence	What to do
Metformin (diabetes medicine) prescription	Not explained in the sources read.	Metformin use is linked to more B12 deficiency (OR 2.95), with more deficiency at longer use and higher metformin amounts. The NHS lists metformin as a medicine that can reduce B12.	Meta analysis of mostly cross sectional studies and authoritative guidance Low certainty ^{9 24}	Ask your doctor or pharmacist whether your B12 should be checked. Do not stop metformin on your own.
Proton pump inhibitors (acid reducers such as omeprazole) prescription and over-the-counter	Not explained in the sources read.	B12 deficiency was somewhat more common in PPI users (OR 1.42), but most studies found no difference in average blood B12 and the authors call the link unclear. The NHS lists PPIs as medicines that can affect B12.	Meta analysis of observational studies and authoritative guidance Low certainty ^{3 24}	Ask a doctor or pharmacist about B12 checks if you use these for a long time.
Nitrous oxide recreational and medical gas	Not explained in the sources read.	The NHS lists nitrous oxide as able to lower B12. A case series describes spinal cord and nerve damage after recreational use.	Case series and authoritative guidance Low certainty ^{16 24}	Tell your doctor if you use nitrous oxide, and see a doctor urgently for numbness, weakness or balance problems.
Anticonvulsant (epilepsy) medicines prescription	Not explained in the sources read.	The NHS says certain medicines, including anticonvulsants and PPIs, can affect how much of these vitamins (B12 and folate) the body absorbs.	Authoritative guidance Low certainty ²⁵	Ask your prescriber or pharmacist; do not change anticonvulsants on your own.
High-dose folic acid (vitamin B9) supplement	Folic acid can correct the anaemia of B12 deficiency while the B12 shortage and nerve damage continue (NHS, review).	May hide low B12. A review also links high folic acid with worse markers when B12 is low, but calls the evidence correlative.	Authoritative guidance and narrative review Low certainty ^{26 14}	Have B12 checked before folic acid treatment (the NHS does this).
Other medicines said to lower B12 (for example H2 acid blockers, colchicine, neomycin, chloramphenicol) prescription	Not read.	These are often named in clinical references but were not found in a source read for this page, so nothing is stated as fact.	Not verified Not enough evidence	Ask a pharmacist.

Who should check first 6

Situation	Advice	Evidence
Pregnancy and breastfeeding	MedlinePlus gives the US Recommended Dietary Allowance as 2.6 mcg a day in pregnancy and 2.8 mcg a day while breastfeeding for teens and women (2.4 mcg for other adults). These are intake targets, not advice to take pills. A 2024 Cochrane review found B12 in pregnancy may raise B12 levels but outcomes for mother and baby are uncertain, and it found no neural tube defect trial. Exclusively breast-fed babies of mothers with low B12 can become deficient, with developmental harm. Ask a doctor or midwife; the NHS says to avoid liver in pregnancy.	Authoritative guidance, systematic review and review ^{22 6 7 23}
Infants and children	MedlinePlus gives Adequate Intakes of 0.4 mcg (0 to 6 months) and 0.5 mcg (7 to 12 months) a day and Recommended Dietary Allowances of 0.9 (1 to 3 years), 1.2 (4 to 8) and 1.8 mcg (9 to 13) a day. These are intake targets. Children on vegan or macrobiotic diets had lower blood B12 in a meta-analysis. B12 products for children should be chosen with a doctor or pharmacist.	Authoritative guidance and meta analysis ^{22 8}
Pernicious anaemia or other conditions that block absorption	The NHS says pernicious anaemia, stomach surgery and gut conditions such as Crohn disease can stop B12 being absorbed from food, and that treatment is chosen by a doctor, often injections for life. Over-the-counter pills may not be the right treatment.	Authoritative guidance ^{24 26}
Allergy to B12 injections or to cobalt-containing products	A rare severe allergic reaction to a cyanocobalamin injection has been reported. A cobalt allergy link was not checked in the sources read. People who have had a reaction to B12 should tell their doctor.	Case report ¹
Men who smoke or have smoked	The VITAL cohort link between individual B12 supplements and lung cancer was stronger in smoking men. This does not prove cause. Ask a doctor about supplements.	Prospective cohort ²
Kidney disease	No source read on kidney disease and B12 forms. The Cochrane stroke review excluded people with end-stage kidney disease. Ask a kidney doctor.	Not researched ¹³

Overdose, product quality and regulators

Summary. B12 is water-soluble. MedlinePlus says leftover amounts leave the body in the urine after the body has used what it needs. The NHS says there is not enough evidence to show what high daily doses of supplements may do, but that the Department of Health and Social Care advises not taking too much, and that 2 mg a day or less is unlikely to cause harm. The US limit position could not be checked (NIH page blocked).

Animal. Not reviewed.

High dose or long term signals. Observational links, not proven harm: individual B12 supplements and lung cancer in men (VITAL), and higher blood B12 with prostate cancer (meta-analysis, OR 1.10 per 100 pmol/L). High blood B12 can reflect other illness, so the cause is not known.

Overdose response. No overdose information was found in the sources read.

Genotoxicity. Not researched.

Contamination and label accuracy of B12 products were not researched. No source on this was read.

Hidden B12 in other products. B12 is in almost all multivitamins, B-complex pills, fortified cereals and some nutritional yeast products (MedlinePlus), so amounts from several products add up. ²²

Body	Action	Date
MedlinePlus (US National Library of Medicine) (United States)	Lists Recommended Dietary Allowances for B12: infants 0 to 6 months 0.4 mcg (Adequate Intake), 7 to 12 months 0.5 mcg; children 1 to 3 years 0.9 mcg, 4 to 8 years 1.2 mcg, 9 to 13 years 1.8 mcg; ages 14 and over 2.4 mcg; pregnancy 2.6 mcg; breastfeeding 2.8 mcg a day. It states no upper limit. source	2025-01-21
NHS (UK), citing the Department of Health and Social Care (United Kingdom)	Says adults aged 19 to 64 need about 1.5 mcg a day, that there is not enough evidence to show the effects of high doses, and that 2 mg or less a day of supplements is unlikely to cause harm. source	2020-08-03
NHS (UK) (United Kingdom)	Explains B12 deficiency anaemia, its causes (including PPIs, metformin and nitrous oxide) and treatment (hydroxocobalamin injections preferred over cyanocobalamin). source	2023-02-20

When to get medical help

Numbness, pins and needles, weakness, trouble walking or balance, or confusion that is new or getting worse: see a doctor soon, because nerve damage from low B12 can become permanent.
These symptoms after using nitrous oxide (laughing gas): get medical help urgently.
Swelling of the face or throat, trouble breathing, a fast heartbeat or collapse after a B12 injection or tablet: call emergency services.
Extreme tiredness, breathlessness, pale skin or a sore red tongue: see a doctor for a blood test (possible anaemia or low B12).
A baby who is breastfed by a mother who eats no animal foods and who is floppy, vomiting, unusually sleepy, or losing skills: get medical help straight away.

Stop using the product and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.

General information only, not medical advice. Ask a clinician or pharmacist before use, especially with medicines, in pregnancy or with a health condition. See the Natural Remedy Safety guide.

Frequently asked questions

What is vitamin B12?

Vitamin B12 (cobalamin) is a water-soluble B vitamin. It helps form red blood cells, keeps the nervous system healthy and helps the body use folate. The liver stores a few years' worth.

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What foods have vitamin B12?

Only animal foods have it naturally: clams, beef liver, fish, meat, eggs, milk and cheese. By USDA data, 3 oz of cooked clams has about 84 mcg and a cup of 2% milk about 1.3 mcg. Fortified cereals and some yeast products also contain it.

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Can you get B12 from plants?

Not from unfortified plant foods. MedlinePlus says B12 is not present in plant foods unless they are fortified, and the NHS says vegans without fortified foods or supplements are at risk of deficiency. Check the label of fortified foods.

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What are the signs of low B12?

The NHS lists extreme tiredness, pins and needles, a sore red tongue, mouth ulcers, muscle weakness, vision problems, mood changes, and memory and judgement problems. These can have other causes, so a blood test is needed.

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Who is most likely to be low?

MedlinePlus lists people over 50, vegetarians and vegans, people who have had stomach or gut surgery, people with coeliac or Crohn disease, and people with pernicious anaemia. Metformin and acid reducers are also linked to lower B12.

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Do tablets work as well as injections?

In a 2018 Cochrane review of 3 small trials, high-dose tablets raised blood B12 about as much as injections, with low certainty and no symptom results. In the UK, the NHS describes injections first for deficiency. A doctor decides.

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Does B12 give you more energy?

If tiredness comes from low B12, correcting it should help. For people who are not low, evidence that extra B12 raises energy is insufficient: only one trial of unexplained tiredness was found.

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Does B12 help memory or mood?

In 16 trials in people who were not clearly deficient, B12 did not improve thinking, memory or depression scores. B12 deficiency itself can cause memory and mood problems, which is a different situation.

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Does B12 protect the heart?

Not shown. In 15 trials of B6, folate and B12, mostly combined, heart attacks and deaths did not change and strokes fell slightly (risk ratio 0.90). The effect of B12 alone is not known.

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Can folic acid hide low B12?

Yes, that is a known concern. The NHS says folic acid can improve symptoms so much that it hides an underlying B12 deficiency, so B12 is checked first. A 2024 review calls evidence on worsening mostly correlative.

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Is taking a lot of B12 safe?

The NHS says there is not enough evidence on high doses and that 2 mg or less a day is unlikely to cause harm. A large US cohort linked individual B12 supplements to more lung cancer in men, but that does not prove cause. Ask a doctor or pharmacist.

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Does B12 matter in pregnancy and for babies?

Deficiency in a breastfeeding mother can lead to B12 deficiency and developmental problems in her baby. A 2024 Cochrane review found B12 in pregnancy may raise B12 levels, but evidence on birth outcomes is very uncertain. Ask a doctor or midwife.

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Editorial transparency

Written by: AlternativeMed editorial team. Research compiled with AI assistance, then checked against the sources listed.
Medical review: None. This page has not been reviewed by a physician or pharmacist.
First published: 2026-10-26
Last substantive update: 2026-10-26
How we research: We started from our existing vitamin B12 summary, read MedlinePlus and three NHS pages, re-checked food values in saved USDA FoodData Central data, and re-read PubMed abstracts for reviews, trials, cohort studies and case reports. Only abstracts were read for studies. The NIH Office of Dietary Supplements page was blocked and is marked unread.
How we rate evidence: See "How we rate evidence" in the Evidence tab.
Independence: No product is promoted on this page. No affiliate links are shown. One adult diet review was written by employees of a fortified-food company, and trials of B12 products may have manufacturer links not stated in abstracts.

Sources 28

Each source was opened and checked. Where we read only the abstract, it says so. The small numbers in the text point here.

Bilwani F, Adil SN, Sheikh U. Anaphylactic reaction after intramuscular injection of cyanocobalamin (vitamin B12): a case report.. J Pak Med Assoc. 2005. PMID 15960291. (abstract)
Brasky TM, White E, Chen CL. Long-Term, Supplemental, One-Carbon Metabolism-Related Vitamin B Use in Relation to Lung Cancer Risk in the Vitamins and Lifestyle (VITAL) Cohort.. J Clin Oncol. 2017. PMID 28829668. DOI 10.1200/JCO.2017.72.7735. (abstract)
Choudhury A, Jena A, Jearth V, et al.. Vitamin B12 deficiency and use of proton pump inhibitors: a systematic review and meta-analysis.. Expert Rev Gastroenterol Hepatol. 2023. PMID 37060552. DOI 10.1080/17474124.2023.2204229. (abstract)
Collin SM, Metcalfe C, Refsum H, et al.. Circulating folate, vitamin B12, homocysteine, vitamin B12 transport proteins, and risk of prostate cancer: a case-control study, systematic review, and meta-analysis.. Cancer Epidemiol Biomarkers Prev. 2010. PMID 20501771. DOI 10.1158/1055-9965.EPI-10-0180. (abstract)
Field DT, Cracknell RO, Eastwood JR, et al.. High-dose Vitamin B6 supplementation reduces anxiety and strengthens visual surround suppression.. Hum Psychopharmacol. 2022. PMID 35851507. DOI 10.1002/hup.2852. (abstract)
Finkelstein JL, Fothergill A, Venkatramanan S, et al.. Vitamin B12 supplementation during pregnancy for maternal and child health outcomes.. Cochrane Database Syst Rev. 2024. PMID 38189492. DOI 10.1002/14651858.CD013823.pub2. (abstract)
Hasbaoui BE, Mebrouk N, Saghir S, et al.. Vitamin B12 deficiency: case report and review of literature.. Pan Afr Med J. 2021. PMID 34046142. DOI 10.11604/pamj.2021.38.237.20967. (abstract)
Jensen CF. Vitamin B12 levels in children and adolescents on plant-based diets: a systematic review and meta-analysis.. Nutr Rev. 2023. PMID 36413044. DOI 10.1093/nutrit/nuac096. (abstract)
Kakarlapudi Y, Kondabolu SK, Tehseen Z, et al.. Effect of Metformin on Vitamin B12 Deficiency in Patients With Type 2 Diabetes Mellitus and Factors Associated With It: A Meta-Analysis.. Cureus. 2022. PMID 36628003. DOI 10.7759/cureus.32277. (abstract)
Kang D, Shi B, Erfe MC, et al.. Vitamin B12 modulates the transcriptome of the skin microbiota in acne pathogenesis.. Sci Transl Med. 2015. PMID 26109103. DOI 10.1126/scitranslmed.aab2009. (abstract)
Malouf R, Areosa Sastre A. Vitamin B12 for cognition.. Cochrane Database Syst Rev. 2003. PMID 12918012. DOI 10.1002/14651858.CD004326. (abstract)
Markun S, Gravestock I, Jager L, et al.. Effects of Vitamin B12 Supplementation on Cognitive Function, Depressive Symptoms, and Fatigue: A Systematic Review, Meta-Analysis, and Meta-Regression.. Nutrients. 2021. PMID 33809274. DOI 10.3390/nu13030923. (abstract)
Marti-Carvajal AJ, Sola I, Lathyris D, et al.. Homocysteine-lowering interventions for preventing cardiovascular events.. Cochrane Database Syst Rev. 2017. PMID 28816346. DOI 10.1002/14651858.CD006612.pub5. (abstract)
Miller JW, Smith A, Troen AM, et al.. Excess Folic Acid and Vitamin B12 Deficiency: Clinical Implications?. Food Nutr Bull. 2024. PMID 38987872. DOI 10.1177/03795721241229503. (abstract)
Neufingerl N, Eilander A. Nutrient Intake and Status in Adults Consuming Plant-Based Diets Compared to Meat-Eaters: A Systematic Review.. Nutrients. 2021. PMID 35010904. DOI 10.3390/nu14010029. (abstract)
Patel SG, Zhang T, Liem B, et al.. Nitrous oxide myelopathy: a case series.. N Z Med J. 2024. PMID 39024584. DOI 10.26635/6965.6477. (abstract)
Ruan J, Gong X, Kong J, et al.. Effect of B vitamin (folate, B6, and B12) supplementation on osteoporotic fracture and bone turnover markers: a meta-analysis.. Med Sci Monit. 2015. PMID 25805360. DOI 10.12659/MSM.893310. (abstract)
Sawangjit R, Thongphui S, Chaichompu W, et al.. Efficacy and Safety of Mecobalamin on Peripheral Neuropathy: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.. J Altern Complement Med. 2020. PMID 32716261. DOI 10.1089/acm.2020.0068. (abstract)
Wang H, Li L, Qin LL, et al.. Oral vitamin B(12) versus intramuscular vitamin B(12) for vitamin B(12) deficiency.. Cochrane Database Syst Rev. 2018. PMID 29543316. DOI 10.1002/14651858.CD004655.pub3. (abstract)
Wang Z, Zhu W, Xing Y, et al.. B vitamins and prevention of cognitive decline and incident dementia: a systematic review and meta-analysis.. Nutr Rev. 2022. PMID 34432056. DOI 10.1093/nutrit/nuab057. (abstract)
den Elzen WP, van der Weele GM, Gussekloo J, et al.. Subnormal vitamin B12 concentrations and anaemia in older people: a systematic review.. BMC Geriatr. 2010. PMID 20573208. DOI 10.1186/1471-2318-10-42. (abstract)
. MedlinePlus Medical Encyclopedia: Vitamin B12 (review date 2025-01-21). . . (full-text)
. NHS: Vitamins and minerals, B vitamins and folic acid (vitamin B12 section; page last reviewed 2020-08-03). . . (full-text)
. NHS: Vitamin B12 or folate deficiency anaemia, causes (page last reviewed 2023-02-20). . . (full-text)
. NHS: Vitamin B12 or folate deficiency anaemia, overview, symptoms and complications (page last reviewed 2023-02-20). . . (full-text)
. NHS: Vitamin B12 or folate deficiency anaemia, treatment (page last reviewed 2023-02-20). . . (full-text)
. NIH Office of Dietary Supplements: Vitamin B12 fact sheet for health professionals. . . (not-read)
. USDA FoodData Central, SR Legacy (April 2018 release): vitamin B-12 content of common foods. . . (full-text)

Where to buy

Check the label first. Whatever you buy, look for these:

The amount of the active ingredient per serving, not just the front-label claim
A third-party testing mark (USP, NSF or ConsumerLab)
Other ingredients and allergens
Ask a pharmacist about interactions with your medicines

Talk to a pharmacist or doctor before you start any supplement, especially if you take medicines. See the Safety tab for interactions.

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Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.