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Vitamin B12

A vitamin found naturally in animal foods such as fish, meat, eggs and dairy. In a US survey, 24% of men and 29% of women reported using a supplement with it.

Explained simply · Last reviewed 2026-09-26

What it is

Vitamin B12 is a water-soluble vitamin found naturally in foods from animals. The Office of Dietary Supplements (ODS), part of the US National Institutes of Health, says that in a US national survey from 2017 to March 2020, about 24% of men and 29% of women reported using a supplement containing it. It notes that vitamin B12 is often promoted as an energy enhancer and an athletic performance and endurance booster, because of its role in energy metabolism.

More about Vitamin B12

The Office of Dietary Supplements (ODS), part of the US National Institutes of Health, says that in a US national survey from 2017 to March 2020, about 24% of men and 29% of women reported using a supplement containing it. It notes that vitamin B12 is often promoted as an energy enhancer and an athletic performance and endurance booster, because of its role in energy metabolism.

ODS explains that vitamin B12 contains the mineral cobalt, so compounds with vitamin B12 activity are collectively called cobalamins. It states that the body needs vitamin B12 for the development and function of the central nervous system, for healthy red blood cell formation, and for DNA synthesis.

ODS names fish, meat, poultry, eggs and dairy products as natural sources. It says plant foods do not naturally contain vitamin B12, but some are fortified with it, including many breakfast cereals and nutritional yeasts. It states that most people in the United States consume enough vitamin B12, and it names groups more likely to run low, listed under how to take it.

ODS describes the vitamin B12 in food as bound to protein, which stomach acid and enzymes must release before it is absorbed. The freed vitamin then combines with intrinsic factor, a protein made by the stomach, and is absorbed in the small intestine. ODS notes that the vitamin B12 added to fortified foods and supplements is already in free form, so it skips that first step.

ODS states that cyanocobalamin is the most common form in supplements, and that other forms are also used. The claims below report what the cited reviews and ODS found when people took vitamin B12, usually with other B vitamins.

Also known as: cobalamin, cyanocobalamin, methylcobalamin, adenosylcobalamin, hydroxycobalamin, hydroxocobalamin

At a glance

Safety: known risks, 1 group who should avoid it or take extra care and 2 documented interactions. See Safety ↓

Claims made about Vitamin B12, and how strong the evidence is for each:

Protects memory and thinking, or prevents dementia, in older adultsEvidence rating: Evidence against
Relieves depressive symptoms in people without major depressionEvidence rating: Evidence against
Prevents heart attacksEvidence rating: Evidence against
Lowers the risk of strokeEvidence rating: Limited
Improves athletic performance or endurance in people with sufficient vitamin B12 statusEvidence rating: Insufficient

Longevity and aging claims

Claims made about Vitamin B12 and aging, and how strong the evidence is for each. A change in a marker is not the same as a longer life.

Lowers the risk of death from any cause when combined with other B vitaminsEvidence rating: Evidence against

Each rating follows our published rules and the sources cited for it. We don’t add our own medical judgment. How we rate

Safety

Read this before the ratings below.

Risks

ODS reports that no upper limit has been set for vitamin B12 because of its low potential for toxicity, and that even at large doses it is generally considered to be safe.
ODS describes the evidence on vitamin B12 and cancer as mixed. Some observational studies and limited trial evidence link higher intakes or blood levels with cancer: in one cohort, long-term use of supplemental vitamin B12 was associated with a higher risk of lung cancer in men but not in women, and in one trial of folic acid with vitamin B12, colorectal cancer was more common in the supplement group, which ODS notes might be due to the folic acid rather than the vitamin B12; in that trial the supplements had no significant effect on overall cancer risk.
ODS also reports that other studies, including a meta-analysis of 18 trials of B vitamins, found little or no effect on cancer, and that some evidence links lower vitamin B12 levels or intakes with a higher risk of certain cancers. It says more research is needed.
A 2017 Cochrane review of homocysteine-lowering B vitamins analyzed cancer as its serious adverse event. Across eight trials (35,788 people) it describes the effect on cancer incidence compared with placebo as uncertain (8.27% against 8.50%; risk ratio 1.07, 95% CI 1.00 to 1.14; high-quality evidence). Across three trials (13,802 people) it also found no clear difference in other adverse events, serious or not (risk ratio 1.02, 95% CI 0.88 to 1.19; high-quality evidence).
A 2018 Cochrane review of B vitamins for cognition reports "very sparse data on adverse effects". In one of its trials, in people with a recent heart attack, unstable angina or stroke, more people died in the group given a combination of folate, vitamin B6 and vitamin B12 than in the placebo group (7.5% against 4.1%; very low-certainty evidence). In a trial of 3,668 people with a recent ischemic stroke, 5.4% died in the B-vitamin group and 6.3% in the comparison group over two years (risk ratio 0.9, 95% CI 0.7 to 1.1). In a trial of 12,064 people who had had a heart attack, deaths did not clearly differ (risk ratio 1.03, 95% CI 0.95 to 1.12; moderate-certainty evidence).
A 2021 review of vitamin B12 for cognition and mood notes that recent observational studies have linked vitamin B12 supplementation or blood levels with hip fractures, lung cancer and, in the general population, death from any cause.

Who should avoid it or take extra care

ODS advises that anyone taking the medications listed below, or other medications, on a regular basis should discuss their vitamin B12 status with their health care providers.

Documented interactions

Gastric acid inhibitors: proton pump inhibitors (for example omeprazole/Prilosec, lansoprazole/Prevacid) and H2 blockers (for example cimetidine/Tagamet, ranitidine): ODS reports that these medications can interfere with the absorption of vitamin B12 from food by slowing the release of stomach acid, and so can lead to vitamin B12 deficiency. Source [1]
Metformin: ODS reports that metformin might reduce the absorption of vitamin B12 and significantly reduce serum levels of vitamin B12. Source [1]

Safety sources: Source [1]Source [2]Source [3]Source [4]

What the evidence says

Each claim is rated on its own evidence. Ratings follow the scale on our methodology page.

Protects memory and thinking, or prevents dementia, in older adults Evidence rating: Evidence against
People take it hoping it will keep their memory and thinking sharp as they get older.
Two reviews found no evidence that B vitamins improve memory or thinking in older adults, at mostly moderate or low certainty, some very low; Cochrane calls its dementia data very sparse.
A 2021 systematic review pooled 16 randomized trials in 6,276 older adults without advanced neurological disorders or overt vitamin B12 deficiency. Across the 11 trials that measured cognitive function, the review found no evidence of an effect of vitamin B12 on executive function, memory, global cognition or processing speed. That held for vitamin B12 alone (four trials) and with folic acid, with or without vitamin B6. The reviewers rated how sure they could be of each (certainty) as moderate. They concluded: "Vitamin B12 supplementation is likely ineffective for improving cognitive function and depressive symptoms in patients without advanced neurological disorders." The longest treatment they found lasted two years, and they note that the effect of longer-term supplementation remains unanswered.

A 2018 Cochrane review of 14 trials in 27,882 cognitively healthy adults tested folic acid, vitamin B6 or vitamin B12, alone or combined. Its participants were mainly in their 60s and 70s, and mostly had a history of heart or blood-vessel disease. Only one of its trials tested vitamin B12 alone. The reviewers found that B vitamins probably have little or no effect on overall cognitive function up to 5 years (moderate certainty) and may have none at 5 to 10 years (low certainty). Their certainty for memory, executive function and processing speed ranged from high for one measure to very low for several.

The Cochrane reviewers report "very sparse data on adverse effects or on incidence of cognitive impairment or dementia". One trial found no difference in new cases of cognitive impairment (moderate certainty; the results text gives a risk ratio of 1.01, 95% CI 0.69 to 1.48, and the summary table 0.89, 95% CI 0.67 to 1.18). A long-term follow-up of another gave an imprecise result favoring B vitamins (odds ratio 0.72, 95% CI 0.25 to 2.09; very low certainty). A third reported similar numbers developing dementia in each group (43 against 38). The same review reports more deaths in the B-vitamin group of one trial, on very low-certainty evidence; see the safety section.

ODS states that, in general, trials do not show that vitamin B12 alone or with folic acid, vitamin B6 or both for one to two years improves cognitive function in older adults with or without dementia, mild cognitive impairment or Alzheimer's disease. It also states that supplementation with vitamin B12 alone or with other B vitamins does not appear to decrease the risk or slow the progression of dementia or Alzheimer's disease in older adults. It calls for more trials. The 2021 review did not analyze new cases of dementia, and the Cochrane review describes those data as very sparse. So the ODS statement is the main source on this page for the risk of dementia.

Sources: Source [1]Source [2]Source [3]
Relieves depressive symptoms in people without major depression Evidence rating: Evidence against
People who feel low take it hoping it will lift their mood.
A 2021 review of six trials, which left out trials in people with major depression, found no overall effect on depressive symptoms and rated that finding moderate certainty.
A 2021 systematic review of vitamin B12 found no overall effect of supplementation on depressive symptoms across six trials, rated moderate certainty. Only one of the six tested vitamin B12 alone, too few for a separate analysis. The others gave it with folic acid, with or without vitamin B6.

The review excluded trials in people with major depression or psychotic disorders. Its authors say this increases the applicability of the results "to predominantly less severely depressed patients". Their conclusion covers depressive symptoms as well as cognitive function: "Vitamin B12 supplementation is likely ineffective for improving cognitive function and depressive symptoms in patients without advanced neurological disorders."

None of the trials in the review was aimed at people with major depression, so this page's rating does not cover them.

Sources: Source [1]
Prevents heart attacks Evidence rating: Evidence against
People take it hoping it will lower their risk of a heart attack.
A 2017 Cochrane review of 12 trials of B vitamins, none of vitamin B12 alone, found no difference in heart attacks compared with placebo and rated that evidence high quality.
A 2017 Cochrane review of 15 trials in 71,422 people tested B vitamins that lower homocysteine, a blood marker, mostly in adults who already had cardiovascular disease. The review lists most of its trials as testing vitamins B6, B12 and folic acid together, and five as testing folic acid only; none is listed as testing vitamin B12 alone. In the review, the vitamins made no difference to heart attacks compared with placebo (risk ratio 1.02, 95% CI 0.95 to 1.10; 12 trials, 46,699 people). The review also found no difference in death from any cause (risk ratio 1.01, 95% CI 0.96 to 1.06; 11 trials, 44,817 people). The reviewers rated both findings high-quality evidence.

ODS explains that vitamin B12 is needed to convert homocysteine to methionine. It says raised homocysteine has been associated with a higher risk of cardiovascular disease, and that researchers hypothesized B vitamin supplements could reduce that risk by lowering homocysteine. It reports that trials have found vitamin B12 and folic acid supplements lower homocysteine, but not cardiovascular risk. It concludes: "Overall, the available evidence suggests that supplementation with vitamin B12 alone or in combination with other B-vitamins does not reduce the risk of CVD or of CVD-related death."

Sources: Source [1]Source [2]
Lowers the risk of stroke Evidence rating: Limited
People take it hoping it will lower their risk of a stroke.
A 2017 Cochrane review found slightly fewer strokes with B vitamins, none given as vitamin B12 alone, and rated that high quality, but its authors say the result appears to be weak.
A 2017 Cochrane review found that B vitamins which lower homocysteine, a blood marker, reduced stroke slightly compared with placebo. Of the people taking them, 4.3% had a stroke, against 5.1% on placebo (risk ratio 0.90, 95% CI 0.82 to 0.99; 10 trials, 44,224 people). The reviewers rated this high-quality evidence.

Nine of those ten trials enrolled people with a history of cardiovascular disease. The review lists one of the ten as testing folic acid only and the other nine as testing combinations of vitamins B6, B12 and folic acid. It lists none that tested vitamin B12 alone.

Restricted to the trials at low risk of bias, the reduction was no longer statistically significant (risk ratio 0.90, 95% CI 0.80 to 1.02). The reviewers write that "this result should be viewed with caution" and that "This positive result appears to be weak".

The ODS vitamin B12 fact sheet does not mention this stroke finding. It concludes: "Overall, the available evidence suggests that supplementation with vitamin B12 alone or in combination with other B-vitamins does not reduce the risk of CVD or of CVD-related death." The review's authors call this result weak, and ODS concludes that the available evidence suggests vitamin B12 does not reduce cardiovascular risk. For these two reasons, this page rates the claim limited.

Sources: Source [1]Source [2]
Improves athletic performance or endurance in people with sufficient vitamin B12 status Evidence rating: Insufficient
Active people take it hoping it will give them more energy and endurance for exercise.
ODS says vitamin B12 does not appear to improve performance or endurance in people with enough of it, citing a 2004 review article and one trial of a multi-ingredient product.
The only cited source is ODS. It states that vitamin B12 supplementation does not appear to improve athletic performance or endurance in people who have sufficient vitamin B12 status. It adds that vitamin B12 supplementation appears to have no beneficial effect on performance in the absence of a nutritional deficit.

ODS gives two references for this. One is a 2004 review article on vitamin and mineral status and physical performance. The other is one trial of a pre-workout supplement that combined vitamin B12 with many other ingredients. No systematic review of vitamin B12 and athletic performance is cited.

Under this site's rules, an insufficient rating means the cited evidence is too limited to show whether there is an effect. It does not mean the sources found no effect.

Sources: Source [1]

Longevity and aging

What the cited sources report about lifespan, death from any cause, and markers studied in connection with aging. A change in a marker is not the same as a longer life. Each outcome is rated on its own evidence, on the same scale as the claims above.

Lowers the risk of death from any cause when combined with other B vitamins Evidence rating: Evidence against
People take it hoping it will help them live longer.
A 2017 Cochrane review of 11 trials of B vitamins, none giving vitamin B12 alone, found no difference in death from any cause and rated that evidence high quality.
No cited trial tested vitamin B12 on its own for this outcome. A 2017 Cochrane review pooled 11 trials in 44,817 people, followed for 1 to 7.3 years. They compared B vitamins which lower homocysteine, a blood marker, with placebo or standard care. The review found no difference between the groups in death from any cause (11.7% against 12.3%; risk ratio 1.01, 95% CI 0.96 to 1.06), which it rated high-quality evidence. The seven trials at low risk of bias gave a similar result (risk ratio 1.03, 95% CI 0.95 to 1.12).

The review groups ten of the trials as including people with a history of cardiovascular disease. Nine gave vitamin B12 together with folic acid or another folate (5-MTHF), with or without vitamin B6, and two of those also had a group given vitamin B6 alone. The other two gave folic acid alone. None gave vitamin B12 alone. For adults without cardiovascular disease, this analysis holds one trial, of 490 people, too imprecise to show an effect either way (risk ratio 0.20, 95% CI 0.01 to 4.04).

The reviewers' trial sequential analysis concluded that no more trials are needed for this outcome. A Bayes factor analysis they also report found that the data did not favor either hypothesis.

ODS describes the review as concluding that supplements of vitamin B12 alone or with other B vitamins do not reduce death rates in people at risk of or with cardiovascular disease, although the review lists no trial of vitamin B12 alone. It also reports that a meta-analysis of 18 trials in 74,498 people found that supplements containing B vitamins had little or no effect on death from any cause. Those supplements included vitamin B12, and follow-up ran from 2 to 7.3 years. The safety section describes deaths reported in individual trials of B vitamins for memory and thinking. It also covers observational studies linking vitamin B12 supplementation or blood levels with death from any cause.

Sources: Source [1]Source [2]

How and when to take it

What the cited sources say about taking it. Ask your doctor or pharmacist what applies to you.

Some groups are more likely to run low on vitamin B12
ODS names older adults, people with pernicious anemia or gastrointestinal disorders such as celiac disease or Crohn's disease, people who have had stomach or intestinal surgery, including weight-loss surgery, people who follow vegetarian or vegan diets, and the exclusively breastfed infants of women who follow vegan diets. It also lists prolonged use of certain medications, such as metformin or proton pump inhibitors, among the causes of deficiency. It reports that vegans and vegetarians are at higher risk because natural food sources of vitamin B12 are limited to animal foods, and that fortified foods and vitamin B12 supplements can substantially reduce their risk of deficiency. It notes that the vitamin B12 in supplements and fortified foods is already in free form, so it does not need to be separated from food protein before it is absorbed. Source [1]
No upper limit has been set
ODS reports that no tolerable upper intake level was established for vitamin B12 because of its low potential for toxicity. Source [1]

Which form the evidence used

Supplements are sold in several forms. This is what the sources on this page say about them — which form the research used, and any comparison those sources themselves made. Where they made none, this page does not rank the forms.

Cyanocobalamin, What the sources supportDetails
ODS states that cyanocobalamin is the most common form of vitamin B12 in dietary supplements. The cited Cochrane review of heart attacks and strokes refers to the vitamin B12 in its trials as cyanocobalamin. ODS also states that no evidence indicates that absorption rates of vitamin B12 in supplements vary by form. Source [1]Source [2]
Methylcobalamin, adenosylcobalamin or hydroxycobalamin, Details
ODS lists these as the other forms of vitamin B12 used in supplements. It describes methylcobalamin and 5-deoxyadenosylcobalamin as the metabolically active forms, and explains that hydroxycobalamin and cyanocobalamin become biologically active once the body converts them to one of those two. It states that no evidence indicates that absorption rates of vitamin B12 in supplements vary by form. This is about absorption, not about whether any form helps the claims rated below. Source [1]
Sublingual tablets or lozenges, Details
ODS states that evidence suggests no difference in efficacy between oral and sublingual forms of vitamin B12. The two studies it cites for this compared the routes for correcting vitamin B12 deficiency and for lowering homocysteine, not for any of the claims rated below. Source [1]

Reference intake values

Quoted exactly as published by the cited authority. These are population reference values, not a recommendation for you. Ask your doctor or pharmacist what applies to your situation.

Teens, 14–18 years
Recommended intake
2.4 mcg
Upper limit
Not stated
Source
Source [1]
Adults, 19+ years
Recommended intake
2.4 mcg
Upper limit
Not stated
Source
Source [1]
Pregnancy, 14–18 years
Recommended intake
2.6 mcg
Upper limit
Not stated
Source
Source [1]
Pregnancy, 19+ years
Recommended intake
2.6 mcg
Upper limit
Not stated
Source
Source [1]
Lactation, 14–18 years
Recommended intake
2.8 mcg
Upper limit
Not stated
Source
Source [1]
Lactation, 19+ years
Recommended intake
2.8 mcg
Upper limit
Not stated
Source
Source [1]

Reference intake values as published by the cited health authority
Population	Recommended intake	Upper limit	Source
Teens, 14–18 years	2.4 mcg	Not stated	Source [1]
Adults, 19+ years	2.4 mcg	Not stated	Source [1]
Pregnancy, 14–18 years	2.6 mcg	Not stated	Source [1]
Pregnancy, 19+ years	2.6 mcg	Not stated	Source [1]
Lactation, 14–18 years	2.8 mcg	Not stated	Source [1]
Lactation, 19+ years	2.8 mcg	Not stated	Source [1]

Sources

Effects of Vitamin B12 Supplementation on Cognitive Function, Depressive Symptoms, and Fatigue: A Systematic Review, Meta-Analysis, and Meta-Regression
Nutrients, 2021 · Meta-analysis · Primary source · Certainty: moderate
Vitamin and mineral supplementation for maintaining cognitive function in cognitively healthy people in mid and late life
Cochrane Database of Systematic Reviews, 2018 · Systematic review · Primary source · Certainty: very low
Some of its authors disclose ties to industry.
Vitamin B12: Fact Sheet for Health Professionals
NIH Office of Dietary Supplements, 2025 · Health authority summary · Primary source
Homocysteine-lowering interventions for preventing cardiovascular events
Cochrane Database of Systematic Reviews, 2017 · Systematic review · Primary source · Certainty: high
Some of its authors disclose ties to industry.

Page history

Show all 5 changes to this page

2026-09-27 — Rewritten to the content style guideline; ratings and sources unchanged.
2026-09-26 — Source audit. Removed the fractures claim (rated evidence-against): its only source, a 2024 meta-analysis of B vitamins and bone health, could not be read in full, and no replacement review that meets this site's source rules was found. Removed a 2015 meta-analysis of folate and vitamin B12 for depression, which also could not be read in full. The depression claim keeps its evidence-against rating on the 2021 review and is now worded for people without major depression, the group that review studied. No other rating changed.
2026-09-25 — Added a longevity section. Lowering the risk of death from any cause when combined with other B vitamins is rated evidence-against, from the 2017 Cochrane review of homocysteine-lowering B vitamins already cited on this page; no trial in it tested vitamin B12 alone. No existing claim or rating changed.
2026-09-24 — Published. All six claims, the safety section and every source passed the site's source and wording reviews. One review read from its abstract and one whose main text is paywalled stay logged in docs/08-open-decisions.md.
2026-09-24 — Drafted. Cognition, depression, heart attacks and fractures rated evidence-against; stroke rated limited; athletic performance rated insufficient.