Vitamin B12 · The Ingredient Files

①

Evidence by effect

Evidence strength (A–D, color) and effect size (dots, fill) are shown separately. The two axes are independent.

Claimed effect

Evidence strength

Effect size

One-line summary · key source

Correcting B12 deficiency (megaloblastic/pernicious anemiaMegaloblastic anemia from failure to absorb B12 due to lack of intrinsic factor; corrected by B12 replacement.)Evidence type: Established guideline

A Strong

Large

This is the established evidence that vitamin B12 is an essential nutrient. When B12 is lacking, red blood cells fail to mature properly and megaloblastic anemiaAnemia in which a lack of B12 or folate makes red blood cells abnormally large and immature. develops; the classic cause is pernicious anemiaMegaloblastic anemia from failure to absorb B12 due to lack of intrinsic factor; corrected by B12 replacement., in which a lack of intrinsic factorA stomach protein that enables vitamin B12 absorption in the small intestine; its lack causes pernicious anemia. prevents B12 absorption. Taking B12 corrects this anemia, an established use recognized by the FDA as an indication for cyanocobalaminThe chemical name for vitamin B12; needed for red-blood-cell production and nerve function, and found essentially only in animal foods. injection (pernicious anemia, malabsorption from gastrointestinal surgery or disease, and others). Where there is no malabsorption, a CochraneAn international network that rigorously reviews and synthesizes evidence. review shows high-dose oral B12 (1000 µg a day) normalizes blood B12 as well as intramuscular injection. This is a strength-A core benefit with a clear direction: reversing an anemia caused by a deficiency. PMID: fda-label-cyanocobalamin · 29543316

Preventing or correcting deficiency-related nerve damage (with early replacement)Evidence type: Established guideline

A Strong

Large

The other serious consequence of B12 deficiency is nerve damage, and here B12 replacement is irreplaceable. Prolonged B12 lack damages the nervous system, from peripheral neuropathy to subacute combined degeneration of the spinal cord, and the FDA label states that 'vitamin B12 deficiency that is allowed to progress for longer than 3 months may produce permanent degenerative lesions of the spinal cord.' Critically, taking folic acid instead can make the anemia numbers look better (masking it) but does not prevent the neurological damage, and without B12 replacement irreversible harm results. So when deficiency is suspected, the rule is to replace B12 early, not folic acid. This is a strength-A benefit established in regulation and clinical practice. PMID: fda-label-cyanocobalamin

Preventing deficiency in high-risk groups (vegans, older adults, metformin users)Evidence type: Meta-analysis

B Moderate

Moderate

Because B12 exists essentially only in animal foods and its absorption needs a working gut, certain groups have a clear deficiency risk. A vegan (especially fully plant-based) diet provides almost no dietary B12, so supplements or fortified foods are needed, and older adults absorb less as stomach acid and intrinsic factorA stomach protein that enables vitamin B12 absorption in the small intestine; its lack causes pernicious anemia. decline. Among drugs, metformin is the classic example: in a meta-analysisA statistical synthesis combining results of multiple studies into one conclusion. of 29 cohort and randomized studies (8,089 people), metformin users had about 2.45 times the incidence of B12 deficiency and significantly lower blood B12. Taking B12 in these high-risk groups is an evidence-based preventive step. But this is 'preventing deficiency in at-risk groups,' not a reason for people without deficiency to take more. PMID: 25502588

Improving fatigue, energy, or cognition in people without deficiency (the belief)Evidence type: Meta-analysis

D Insufficient

None

The idea that a 'B12 shot or high dose gives you energy' is central to this ingredient's popularity, but there is no evidence for it in people who are not deficient. In a meta-analysisA statistical synthesis combining results of multiple studies into one conclusion. of 16 randomized trials (6,276 people) in patients without overt B12 deficiency or advanced neurological disorders, B12 alone or combined with folic acid and B6 had no effect on any subdomain of cognitive function and no overall effect on measures of depression. Fatigue could not even be analyzed because only one study reported it. The authors concluded that B12 supplementation is likely ineffective for improving cognition and depressive symptoms in patients without advanced neurological disorders. As an 'energy booster' for people who are not deficient, B12 is not supported by evidence. PMID: 33809274

Preventing heart attack or death (the homocysteineA blood amino acid that rises when folate, B6, or B12 is low; high levels track cardiovascular risk, but lowering it did not reduce cardiac events.-lowering belief)Evidence type: Meta-analysis

D Insufficient

None

B12, together with folate and B6, lowers blood homocysteineA blood amino acid that rises when folate, B6, or B12 is low; high levels track cardiovascular risk, but lowering it did not reduce cardiac events., and because high homocysteine is linked to cardiovascular risk, a 'heart protection' expectation arose. But intervention trials do not support it. In a CochraneAn international network that rigorously reviews and synthesizes evidence. review of 15 randomized trials (71,422 people), lowering homocysteine with B6, B9 (folate), or B12 made no difference versus placeboAn inert dummy treatment used as the comparison baseline. in heart attack (relative risk 1.02), all-cause death (1.01), or serious adverse events (all high-certainty). Only stroke fell slightly (relative risk 0.90). So even though the surrogate marker (homocysteine) drops, actual cardiac events and death do not - the 'homocysteine paradox' - and taking B12 to prevent cardiovascular disease is not supported. PMID: 28816346

Evidence strength A Strong · B Moderate · C Weak · D Insufficient/refuted

Effect size Large → None

②

Who benefits / who should be cautious

The statements in this section are translated directly from institutional sources (NIH-ODS, etc.), not our own interpretation. Consult a professional before use.

Benefit

When B12 deficiency is confirmed it can be corrected by replacement, and unless there is malabsorption (such as pernicious anemiaMegaloblastic anemia from failure to absorb B12 due to lack of intrinsic factor; corrected by B12 replacement.) high-dose oral B12 normalizes blood levels as well as injection. Oral also costs less and is a practical option. source↗

Original text

Low quality evidence shows oral and IM vitamin B12 having similar effects in terms of normalising serum vitamin B12 levels, but oral treatment costs less.
Caution

Taking folic acid instead when deficiency is suspected is dangerous. Folic acid can make the anemia numbers look normal and mask the diagnosis but does not prevent nerve damage, and without B12 replacement irreversible harm can result. Always check B12 status. source↗

Original text

Neurologic manifestations will not be prevented with folic acid, and if not treated with vitamin B 12 , irreversible damage will result.
Caution

Long-term metformin use raises the risk of B12 deficiency. In meta-analysisA statistical synthesis combining results of multiple studies into one conclusion., metformin users had about 2.45 times the deficiency incidence, so long-term users should have their B12 status checked periodically. source↗

Original text

We conclude that metformin treatment is significantly associated with an increase in incidence of VB12 deficiency and reduced serum VB12 levels.
Caution

For people without deficiency, B12 is not an 'energy booster' that lifts fatigue, memory, or mood. In randomized trials of people without advanced neurological disorders or overt deficiency, it had no effect on cognition or depression. source↗

Original text

Vitamin B12 supplementation is likely ineffective for improving cognitive function and depressive symptoms in patients without advanced neurological disorders.
Caution

B12 injections carry rare but serious risks. Anaphylactic shock and death have been reported after parenteral (injected) administration, and patients with early Leber's disease (hereditary optic nerve atrophy) developed swift optic atrophy. Get injections when needed under professional supervision. source↗

Original text

Anaphylactic shock and death have been reported after parenteral vitamin B 12 administration.

③

Form & dosage evidence

Trial doses by effect

Pernicious anemia (FDA label regimen): Intramuscular or deep subcutaneous 100 mcg daily for 6-7 days (then spaced out, lifelong maintenance needed) - oral is unreliable with malabsorption [fda-label-cyanocobalamin]
Deficiency without malabsorption (oral, Cochrane): Oral B12 about 1000 µg/day - similar to injection for normalizing blood levels [29543316]

④

Balanced conclusion

Vitamin B12 is an ingredient whose assessment splits sharply by who takes it. As an essential nutrient, deficiency causes megaloblastic (pernicious) anemia and nerve damage, and B12 replacement correcting these is a strength-A benefit established as an FDA indication. Nerve damage in particular can leave permanent spinal-cord injury if left more than 3 months, and taking folic acid instead masks only the anemia while failing to prevent the nerve damage, so when deficiency is suspected B12 must be checked and replaced early. Vegans, older adults, and long-term metformin users have a clear deficiency risk (metformin about 2.45x) and good reason to take it. Conversely, for people without deficiency B12 is not an 'energy booster' - randomized trials found no effect on fatigue, cognition, or depression, and lowering homocysteineA blood amino acid that rises when folate, B6, or B12 is low; high levels track cardiovascular risk, but lowering it did not reduce cardiac events. did not reduce heart attack or death (only a small stroke reduction). Unless there is malabsorption, high-dose oral B12 is as effective as injection and cheaper, and injections carry a rare anaphylaxis risk, so they are best taken when needed under professional supervision. In short, B12 is an essential nutrient genuinely needed by those who are deficient or at risk, but it is not an all-purpose vitality supplement for healthy non-deficient people, and it can be obtained from animal foods like clams, liver, fish, and meat.

Apply - Get it from food

Examples of foods rich in Vitamin B12. Amounts are shown for reference against the doses used in the trials.

Note: eating these foods does not guarantee immediate treatment or prevention of any disease.

The recommended intake of vitamin B12 for adults is about 2.4 µg a day. In nature B12 is found essentially only in animal foods, so it is abundant in the clams, liver, fish, meat, and eggs below and virtually absent from plant foods (vegetables, grains, legumes). A fully plant-based (vegan) diet therefore needs fortified foods or supplements, and older adults, who absorb less as stomach acid and intrinsic factor decline, benefit from B12-rich foods or supplements.

Clams, cooked100 g ~99 µg [source]
Beef liver, pan-fried100 g ~83 µg [source]
Mackerel, cooked100 g ~19 µg [source]
Salmon, cooked100 g ~3.5 µg [source]
Beef, ground, cooked100 g ~2.7 µg [source]
Egg, hard-boiled100 g ~1.1 µg [source]

⑤

Sources

Each source shows its one-line summary and key summary up front. Expand the collapsed section to read the original abstract. Every citation is verified by re-resolving through the API.

FDA (openFDA) Cyanocobalamin (injection) - drug label (pernicious anemia and malabsorption indications; warnings on folic-acid masking of nerve damage, spinal-cord lesions, anaphylaxis)

This is an institutional information source. Verify directly in the original below.

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PMID 29543316 Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency Systematic review (Cochrane) · Cochrane Database Syst Rev, 2018 3 RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s, 153 people - high-dose oral B12 (1000 µg/day) normalizes blood levels similarly to injection and costs less (low certainty). Oral is an option without malabsorption.

Key summary

A CochraneAn international network that rigorously reviews and synthesizes evidence. systematic review comparing oral versus intramuscular B12 for B12 deficiency. Three randomized trials (153 people) were included, with 3-4 months of treatment. In two trials using 1000 µg/day orally, blood B12 did not differ clinically from injection, and one trial using 2000 µg found oral even higher. Adverse events were similar between routes and oral cost less. The quality of evidence was low to very low due to few trials and participants. The authors concluded that, on low-quality evidence, oral and intramuscular B12 have similar effects on normalizing blood B12 and oral costs less. It suggests oral is a practical option when there is no malabsorption (such as pernicious anemiaMegaloblastic anemia from failure to absorb B12 due to lack of intrinsic factor; corrected by B12 replacement.).

Show original abstract

BACKGROUND: Vitamin B12 deficiency is common, and the incidence increases with age. Most people with vitamin B12 deficiency are treated in primary care with intramuscular (IM) vitamin B12. Doctors may not be prescribing oral vitamin B12 formulations because they may be unaware of this option or have concerns regarding its effectiveness. OBJECTIVES: To assess the effects of oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. MAIN RESULTS: Three RCTs met our inclusion criteria. The trials randomised 153 participants (74 participants to oral vitamin B12 and 79 participants to IM vitamin B12). Treatment duration and follow-up ranged between three and four months. The mean age of participants ranged from 38.6 to 72 years. The treatment frequency and daily dose of vitamin B12 in the oral and IM groups varied among trials. Only one trial had low or unclear risk of bias across all domains and outcome measures. Two trials reported data for serum vitamin B12 levels. The overall quality of evidence for this outcome was low due to serious imprecision (low number of trials and participants). In two trials employing 1000 μg/day oral vitamin B12, there was no clinically relevant difference in vitamin B12 levels when compared with IM vitamin B12. One trial used 2000 μg/day vitamin B12 and demonstrated a mean difference of 680 pg/mL (95% confidence interval 392.7 to 967.3) in favour of oral vitamin B12. Two trials reported data on adverse events (very low-quality evidence due to risk of performance bias, detection bias, and serious imprecision). One trial stated that no treatment-related adverse events were seen in both the oral and IM vitamin B12 groups. One trial reported that 2 of 30 participants (6.7%) in the oral vitamin B12 group left the trial early due to adverse events. Orally taken vitamin B12 showed lower treatment-associated costs than IM vitamin B12 in one trial (low-quality evidence due to serious imprecision). No trial reported on clinical signs and symptoms of vitamin B12 deficiency, health-related quality of life, or acceptability of the treatment scheme. AUTHORS' CONCLUSIONS: Low quality evidence shows oral and IM vitamin B12 having similar effects in terms of normalising serum vitamin B12 levels, but oral treatment costs less. We found very low-quality evidence that oral vitamin B12 appears as safe as IM vitamin B12. ※ The abstract text as collected and stored via the API by the pipeline. The key summary is written based solely on this text.

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PMID 25502588 The role of metformin on vitamin B12 deficiency: a meta-analysis review Meta-analysis · Intern Emerg Med, 2015 29 studies, 8,089 people - metformin users had about 2.45x the B12 deficiency incidence and significantly lower blood B12. Grounds B12 monitoring in long-term users.

Key summary

A meta-analysisA statistical synthesis combining results of multiple studies into one conclusion. of how the type 2 diabetes drug metformin affects B12 deficiency. It pooled 18 retrospective cohort studies and 11 randomized trials, 29 studies in total (8,089 people), with 19 of intermediate to high quality. The main result: metformin users had significantly higher B12 deficiency incidence (odds ratio 2.45, 95% CI 1.74-3.44) and significantly lower blood B12 (mean difference -65.8 pmol/L). Randomized trials alone showed the same trend. The authors concluded metformin use is significantly associated with increased B12 deficiency and reduced blood B12. It supports checking and replacing B12 in long-term users.

Show original abstract

Metformin is the only biguanide oral hypoglycemic drug, that is used to treat patients with type-2 diabetes mellitus. There are some reports of metformin being associated with decreased serum levels of vitamin B12 (VB12). The objective of this study is to systematically analyze the impact of metformin on the frequency of VB12 deficiency and serum levels of VB12. A search of various databases provided 18 retrospective cohort studies and 11 randomized controlled trials. Pooled estimates of odds ratio with 95% confidence interval using random effect model were conducted. Studies were examined for heterogeneity, publication bias and sensitivity analysis. Separate analysis of randomized control trials (RCTs) including both low-risk and high-risk bias was also conducted. 29 studies were selected with a total of 8,089 patients. 19 studies were rated intermediate or high quality. Primary outcome suggested increased incidence of VB12 deficiency in metformin group (OR = 2.45, 95% CI 1.74-3.44, P < 0.0001.) Heterogeneity was relatively high (I(2) = 53%), with minor publication bias. Secondary outcome suggested lower serum VB12 concentrations in metformin group (Mean difference = -65.8, 95% CI -78.1 to -53.6 pmol/L, P < 0.00001) with high heterogeneity (I(2) = 98%,) and low publication bias. RCTs analysis of low-and high-risk group revealed similar trends. We conclude that metformin treatment is significantly associated with an increase in incidence of VB12 deficiency and reduced serum VB12 levels. ※ The abstract text as collected and stored via the API by the pipeline. The key summary is written based solely on this text.

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PMID 33809274 Effects of Vitamin B12 Supplementation on Cognitive Function, Depressive Symptoms, and Fatigue: A Systematic Review, Meta-Analysis, and Meta-Regression Systematic review and meta-analysis · Nutrients, 2021 16 RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s, 6,276 people - in those without deficiency or advanced neuro disease, B12 (alone or combined) had no effect on cognition or depression. Fatigue had only 1 study, unanalyzable. 'Likely ineffective if not deficient.'

Key summary

A meta-analysisA statistical synthesis combining results of multiple studies into one conclusion. of 16 randomized trials (6,276 people) on B12 supplementation's effect on cognition, depression, and fatigue in patients without overt B12 deficiency or advanced neurological disorders. Neither B12 alone nor B12 combined with folic acid and B6 had any effect on any subdomain of cognitive function, and meta-regression found no significant association with dose, duration, or other predictors. There was no overall effect on measures of depression. Fatigue could not be analyzed because only one study reported it. The authors concluded B12 supplementation is likely ineffective for improving cognition and depressive symptoms in patients without advanced neurological disorders. It directly rebuts the belief in B12 as an energy or memory supplement for people who are not deficient.

Show original abstract

Vitamin B12 is often used to improve cognitive function, depressive symptoms, and fatigue. In most cases, such complaints are not associated with overt vitamin B12 deficiency or advanced neurological disorders and the effectiveness of vitamin B12 supplementation in such cases is uncertain. The aim of this systematic review and meta-analysis of randomized controlled trials (RCTs) is to assess the effects of vitamin B12 alone (B12 alone), in addition to vitamin B12 and folic acid with or without vitamin B6 (B complex) on cognitive function, depressive symptoms, and idiopathic fatigue in patients without advanced neurological disorders or overt vitamin B12 deficiency. Medline, Embase, PsycInfo, Cochrane Library, and Scopus were searched. A total of 16 RCTs with 6276 participants were included. Regarding cognitive function outcomes, we found no evidence for an effect of B12 alone or B complex supplementation on any subdomain of cognitive function outcomes. Further, meta-regression showed no significant associations of treatment effects with any of the potential predictors. We also found no overall effect of vitamin supplementation on measures of depression. Further, only one study reported effects on idiopathic fatigue, and therefore, no analysis was possible. Vitamin B12 supplementation is likely ineffective for improving cognitive function and depressive symptoms in patients without advanced neurological disorders. ※ The abstract text as collected and stored via the API by the pipeline. The key summary is written based solely on this text.

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PMID 28816346 Homocysteine-lowering interventions for preventing cardiovascular events Systematic review (Cochrane) · Cochrane Database Syst Rev, 2017 15 RCTRandomized controlled trial - a high-reliability trial that randomly assigns participants to compare effects.s, 71,422 people - lowering homocysteineA blood amino acid that rises when folate, B6, or B12 is low; high levels track cardiovascular risk, but lowering it did not reduce cardiac events. with B6/folate/B12 made no difference in heart attack (RR 1.02) or death (1.01) (high-certainty); only a small stroke reduction (0.90).

Key summary

A CochraneAn international network that rigorously reviews and synthesizes evidence. review of whether homocysteineA blood amino acid that rises when folate, B6, or B12 is low; high levels track cardiovascular risk, but lowering it did not reduce cardiac events.-lowering interventions (vitamins B6, B9, B12 alone or combined) prevent cardiovascular events (15 randomized trials, 71,422 people). Versus placeboAn inert dummy treatment used as the comparison baseline. there was no difference in heart attack (relative risk 1.02), all-cause death (1.01), or serious adverse events, all high-certainty. Only stroke fell slightly (relative risk 0.90, high-certainty). The authors concluded that lowering homocysteine with B6, B9, or B12 makes no difference versus placebo for heart attack, death, or adverse events, with only a small favorable difference for stroke. So the homocysteine number drops but actual cardiac events do not.

Show original abstract

MAIN RESULTS: In this third update, we identified three new randomised controlled trials, for a total of 15 randomised controlled trials involving 71,422 participants. Nine trials (60%) had low risk of bias, length of follow-up ranged from one to 7.3 years. Compared with placebo, there were no differences in effects of homocysteine-lowering interventions on myocardial infarction (homocysteine-lowering = 7.1% versus placebo = 6.0%; RR 1.02, 95% confidence interval (CI) 0.95 to 1.10, I2 = 0%, 12 trials; N = 46,699; Bayes factor 1.04, high-quality evidence), death from any cause (homocysteine-lowering = 11.7% versus placebo = 12.3%, RR 1.01, 95% CI 0.96 to 1.06, I2 = 0%, 11 trials, N = 44,817; Bayes factor = 1.05, high-quality evidence), or serious adverse events (homocysteine-lowering = 8.3% versus comparator = 8.5%, RR 1.07, 95% CI 1.00 to 1.14, I2 = 0%, eight trials, N = 35,788; high-quality evidence). Compared with placebo, homocysteine-lowering interventions were associated with reduced stroke outcome (homocysteine-lowering = 4.3% versus comparator = 5.1%, RR 0.90, 95% CI 0.82 to 0.99, I2 = 8%, 10 trials, N = 44,224; high-quality evidence). Compared with low doses, there were uncertain effects of high doses of homocysteine-lowering interventions on stroke (high = 10.8% versus low = 11.2%, RR 0.90, 95% CI 0.66 to 1.22, I2 = 72%, two trials, N = 3929; very low-quality evidence). We found no evidence of publication bias. AUTHORS' CONCLUSIONS: In this third update of the Cochrane review, there were no differences in effects of homocysteine-lowering interventions in the form of supplements of vitamins B6, B9 or B12 given alone or in combination comparing with placebo on myocardial infarction, death from any cause or adverse events. In terms of stroke, this review found a small difference in effect favouring to homocysteine-lowering interventions in the form of supplements of vitamins B6, B9 or B12 given alone or in combination comparing with placebo. ※ The abstract text as collected and stored via the API by the pipeline. The key summary is written based solely on this text.

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USDA FoodData Central Mollusks, clam, mixed species, cooked, moist heat (FDC 171975)