Vitamin B12, also called cobalamin, is a water-soluble vitamin needed for red blood cell formation, DNA synthesis, and normal nerve function. It is naturally found in foods from animals and is added to some fortified foods and supplements.
Vitamin B12 contains cobalt, which is why compounds with B12 activity are called cobalamins.
Function
Vitamin B12 helps the body:
- Make red blood cells.
- Maintain the nervous system.
- Make DNA.
- Use folate properly.
- Process some fatty acids and amino acids.
Deficiency can affect the blood, nerves, brain, mouth, gut, and general energy levels.
Food Sources
Natural sources include:
- Meat.
- Fish.
- Shellfish.
- Eggs.
- Milk, cheese, and yoghurt.
Plant foods do not naturally provide reliable vitamin B12 unless fortified. Fortified breakfast cereals, fortified plant drinks, nutritional yeast with added B12, and supplements can be important for vegans and some vegetarians.
Absorption
Vitamin B12 in food is released during digestion, then binds to intrinsic factor, a protein made in the stomach. It is absorbed in the final part of the small intestine.
Absorption can be reduced by autoimmune gastritis, stomach or bowel surgery, some bowel diseases, low stomach acid, and some medicines. Older adults and people who avoid animal foods are at higher risk of deficiency.
Deficiency
Vitamin B12 deficiency may cause:
- Tiredness and weakness.
- Pale or yellowish skin.
- Sore red tongue or mouth ulcers.
- Pins and needles.
- Numbness.
- Balance or walking changes.
- Memory, mood, or thinking changes.
- Visual disturbance.
- Megaloblastic anaemia.
Neurological symptoms can occur even without anaemia, so normal haemoglobin does not always rule out clinically important deficiency.
Diagnosis and Treatment
Diagnosis may involve symptoms, blood count, vitamin B12 levels, and sometimes additional tests. NICE guidance covers recognising, diagnosing, and managing vitamin B12 deficiency in people aged 16 and over.
Treatment depends on the cause and severity. NHS guidance describes hydroxocobalamin injections for vitamin B12 deficiency anaemia, while oral replacement can be suitable in some circumstances. People with absorption problems may need long-term treatment.
Supplements and Safety
Vitamin B12 supplements are available in tablets, sprays, drops, and injections. High-dose products are common because only a portion may be absorbed. Vitamin B12 has low toxicity, but unnecessary supplementation can confuse investigation of symptoms if started before testing.
See Also
References
- NIH Office of Dietary Supplements: Vitamin B12 health professional fact sheet
- NIH Office of Dietary Supplements: Vitamin B12 consumer fact sheet
- NICE: Vitamin B12 deficiency in over 16s
- NHS: Vitamin B12 or folate deficiency symptoms
- NHS: Vitamin B12 or folate deficiency treatment
- NHS inform: Vitamin B12 or folate deficiency anaemia
- MedlinePlus: Vitamin B12
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