B12 – kobalaminer, upptag och vad ett forskningsresultat betyder

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URL: https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/
Source date: 2025-07-02
Acquisition: Official NIH page rendered by web reader. Whole selected paragraphs; link markers replaced with their displayed labels only. No HTML/full article file fetched. Not an original clinical trial. Source line capture SHA-256: 700530f0c2a250e814732c3b1bd03bb3afdbd7e2df4c12bcc1132512d87a0bd9

Vitamin B12 is a water-soluble vitamin that is naturally present in some foods, added to others, and available as a dietary supplement and a prescription medication. Because vitamin B12 contains the mineral cobalt, compounds with vitamin B12 activity are collectively called cobalamins [1 ]. Methylcobalamin and 5-deoxyadenosylcobalamin are the metabolically active forms of vitamin B12.

However, two others forms, hydroxycobalamin and cyanocobalamin, become biologically active after they are converted to methylcobalamin or 5-deoxyadenosylcobalamin [1-3 ].

Vitamin B12 is present in many dietary supplements, often as cyanocobalamin, but other forms may also be used. Supplements that only contain vitamin B12 typically have the highest doses of the vitamin, while multivitamin/mineral supplements and supplements that combine vitamin B12 with other B-complex vitamins usually contain lower doses.

Vitamin B12 is available in multivitamin/mineral supplements, in supplements containing other B-complex vitamins, and in supplements containing only vitamin B12. Multivitamin/mineral supplements typically contain vitamin B12 at doses ranging from 5 to 25 mcg [23 ]. Vitamin B12 levels are higher, generally 50 to 500 mcg, in supplements containing vitamin B12 with other B-complex vitamins and even higher, typically 500 to 1,000 mcg, in supplements containing only vitamin B12.

The most common form of vitamin B12 in dietary supplements is cyanocobalamin [1 ,3 ,23 ,24 ]. Other forms of vitamin B12 in supplements are adenosylcobalamin, methylcobalamin, and hydroxycobalamin [23 ].

No evidence indicates that absorption rates of vitamin B12 in supplements vary by form of the vitamin. These rates are about 50% at doses (less than 1–2 mcg) that do not exceed the cobalamin-binding capacity of intrinsic factor and are substantially lower at doses well above 1 to 2 mcg [24 ,25 ]. For example, absorption is only about 2% at doses of 500 mcg and 1.3% at doses of 1,000 mcg [25 ].

In addition to oral dietary supplements, vitamin B12 is available in sublingual preparations as tablets or lozenges [23 ]. Evidence suggests no difference in efficacy between oral and sublingual forms [26 ,27 ].

RCTs have found that vitamin B12 (and folic acid) supplements lower homocysteine levels but not CVD risk. The authors of a Cochrane Review of the effects of homocysteine-lowering interventions on cardiovascular events based on 15 studies in 71,422 participants concluded that supplements of vitamin B12 alone or with other B vitamins do not prevent heart attacks or reduce death rates in people at risk of or with CVD [78 ].

More recently, an extended follow-up of the B-PROOF trial, (which compared 400 mcg folic acid and 500 mcg vitamin B-12 daily with placebo) in 1,298 participants found that after a median of 54 months, the intervention had no effect on CVD risk [79 ].

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.

However, a few observational studies have found no such association [90 ,91 ]. In addition, according to a systematic review of 35 prospective cohort studies in 14,325 participants age 47 to 101 years followed for an average of 5.4 years, the evidence does not support a role for low vitamin B12 in the development of cognitive impairment or dementia [92 ].

In general, evidence from RCTs does not show that vitamin B12 supplementation alone or with folic acid, vitamin B6, or both for 1 to 2 years improves cognitive function in older adults with or without dementia, mild cognitive impairment, or Alzheimer’s disease, even though supplementation lowers homocysteine levels [93-96 ].

For example, an RCT administered 400 mcg/day folic acid and 500 mcg/day vitamin B12 (B-vitamin group) or a placebo for 2 years to 2,919 adults age 65 and older with homocysteine levels of 12 to 50 mcmol/L [95 ]. Although homocysteine concentrations declined significantly more (by 5.0 mcmol/L) in the supplementation group than in the placebo group (1.3 mcmol/L), cognitive test scores did not differ between groups.

A Cochrane Review of vitamin and mineral supplements to maintain cognitive function in cognitively healthy people included 14 studies that compared folic acid, vitamin B12, vitamin B6, or a combination of these supplements to placebo in 27,882 participants, most of whom were age 60 years or older [97 ]. The supplements had little to no effect on global cognitive function when administered for up to 5 years and appeared to have no impact when administered for 5 to 10 years.

Similarly, 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. A Cochrane Review evaluated the effects of vitamin and mineral supplements on cognitive function and dementia in people with mild cognitive impairment [98 ].

The review included five trials with 879 participants that investigated B vitamin supplements (one study of folic acid only and four trials of vitamins B6 and B12 and folic acid). Taking these B vitamins for 6 to 24 months had no apparent effect on episodic memory, executive function, speed of processing, or quality of life, although one study found a slower rate of brain atrophy over 2 years.

Additional clinical trials are needed to better understand the effects of vitamin B12 supplementation on cognitive function and cognitive decline.

Some evidence from observational studies and clinical trials suggests that higher intakes or blood concentrations of vitamin B12 may increase the risk of cancer. However, other evidence contradicts those findings, showing a link between lower intakes or concentrations of vitamin B12 and an increased cancer risk or no link at all. More research is needed to clarify the association between high or low intakes of vitamin B12 and the risk of cancer.

The evidence for a relationship between vitamin B12 and cancer risk is mixed. Some evidence supports a link between increased cancer risk and higher intakes or blood concentrations of vitamin B12, some supports a link with lower intakes or concentrations, and some evidence indicates no link at all.

Vitamin B12 supplements may interact with medications, and some medications, including gastric acid inhibitors and metformin, may affect vitamin B12 levels.

Vitamin B12 supplements have the potential to interact with certain medications. In addition, several types of medications might adversely affect vitamin B12 levels. A few examples are provided below. Individuals taking these and other medications on a regular basis should discuss their vitamin B12 status with their health care providers.

Gastric acid inhibitors include proton pump inhibitors, such as omeprazole (Prilosec) and lansoprazole (Prevacid), and histamine 2-receptor antagonists, such as cimetidine (Tagamet) and ranitidine (Zantac). These drugs are used to treat gastroesophageal reflux disease and peptic ulcer disease. They can interfere with vitamin B12 absorption from food by slowing the release of gastric acid into the stomach and thereby lead to vitamin B12 deficiency [101-103 ].

Metformin, an antihyperglycemic agent used as first-line treatment for prediabetes and diabetes, might reduce the absorption of vitamin B12 and significantly reduce serum vitamin B12 concentrations [103 ].

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Full exact imported definitions of the listed distinct identities; a collection is not an identity merge

{"id":"chebi-176843","version_id":"d19d51a3-0454-4cff-a207-5ded71f90ccd","name":"vitamin B12","definition":"Any member of a group of cobalamin vitamers that exhibit biological activity against vitamin B<small><sub>12</sub></small> deficiency. Vitamin B<small><sub>12</sub></small> deficiency is associated with low red blood cell count and anemia. The vitamers are found in foods such as cereals, meat, fish, and poultry. The vitamers include adenosylcobalamin, hydroxocobalamin, cyanocobalamin, aquacobalamin, nitritocobalamin and methylcobabalamin (also includes their ionized, salt and phosphate derivatives)."}

{"id":"chebi-30411","version_id":"b5a12fdb-a82f-4cba-88b1-a06d5a18a1c5","name":"cobalamin","definition":"A cobalt-corrinoid hexaamide that is cobalamin with the oxidation state of the central cobalt atom unspecified."}

{"id":"chebi-17439","version_id":"21e7bb88-0037-40d3-a3a5-d8958ba99f51","name":"cyanocob(III)alamin","definition":"A complex cob(III)alamin in which cobalt is positioned in the centre of a planar corrin tetrapyrrole ring and bound axially to a 5,6-dimethylbenzimidazole moiety and a cyano group. It is one of several forms of the vitamin known as vitamin B12."}

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Supplement Facts
Serving Size: 1 Tablet
	Amount Per Serving	%Daily Value
Vitamin B-12 (as Cyanocobalamin)	1,000 mcg	41,667%

Cellulose, stearic acid, silica and magnesium stearate.

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Supplement Facts
Serving Size: 1 Tablet
Servings Per Container: 180
	Amount Per Serving	%Daily Value
Vitamin B6 (as pyridoxine hydrochloride)	5 mg	294%
Folate (as 400 mcg folic acid)	667 mcg DFE	167%
Vitamin B12 (as cyanocobalamin)	1,000 mcg	41,667%

Xylitol, mannitol, citric acid, microcrystalline cellulose, natural berry flavor, silicon dioxide, sodium starch glycolate, croscarmellose sodium, sucralose, magnesium stearate. 
Free of sugar, yeast, wheat, egg, artificial colors, flavors, and preservatives.

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Germe de sarrasin, magnésium marin (oxyde de magnésium extrait d’eau de mer), gélule végétale (pullulan).Déclaration nutritionnelle pour 2 gélules :Germe de sarrasin : 712 mgdont vitamine B6 (pyridoxine) : 1,30 mg (93 % des VNR*)dont vitamine B9 (acide folique) : 238 µg (119 % des VNR*)dont vitamine B12 (cobalamine): 2,5 µg (100 % des VNR*).Magnésium : 273 mg (72 % des VNR*)*Valeurs Nutritionnelles de Référence.

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minéral : oxyde de magnésium ; agent de charge : sorbitol ; minéraux : carbonate de magnésium, bisglycinate de magnésium tamponné (bisglycinate de magnésium, oxyde de magnésium) ; stabilisant : gomme xanthane et gomme d'acacia ; anti-agglomérant : sels de magnésium d'acides gras ; vitamines B12 et B6.