Vitamin B12 (Cobalamin)

Vitamin B12 (cobalamin) is needed to make red blood cells, to keep the nervous system healthy, and to release energy from food. Like iron, it sits at the centre of haemoglobin production: without it, the body makes oversized red blood cells that work poorly. This produces a specific type of anaemia (megaloblastic anaemia), and its symptoms overlap with iron deficiency anaemia but are caused differently. A blood test for B12 and folate distinguishes the two.

What makes B12 unusual is its biological origin. It is made by bacteria, not by plants or animals. Grazing animals pick it up from soil bacteria and from the rumen, store it in their tissues, and pass it into milk and eggs. Plants do not make it, so an entirely plant-based diet contains no naturally occurring B12. (Some sea vegetables and fermented foods are sometimes claimed to contain it; the form they contain is largely an inactive analogue and is not a reliable source.) The practical answer for anyone avoiding animal foods is fortified products and a supplement.

Absorption requires a protein made in the stomach lining called intrinsic factor. Older adults, people on certain stomach acid medicines (proton pump inhibitors) long-term, and people who have had gastric surgery may absorb less even when intake is adequate. Pernicious anaemia, an autoimmune condition that damages the intrinsic-factor mechanism, is a known cause of B12 deficiency at any age.

Vitamin B12 from animal foods is delivered generously. The issue is not getting enough as a meat-and-fish eater; it is getting any at all from an unfortified plant-only diet.

Values per 100g come from USDA SR Legacy and McCance and Widdowson 7th edition; the site's food entries currently store macros only.

Liver (lamb or calf) is the single highest natural source of B12 in any normal portion. NHS advice is not to eat liver more than once a week because of its vitamin A content; pregnant women are advised to avoid liver entirely.

For vegans: fortified plant milk, fortified breakfast cereal, fortified nutritional yeast, and a daily B12 supplement together provide a robust supply. Most UK vegan nutrition guidance recommends a supplement rather than relying on fortified foods alone, because fortification varies by brand.

UK Reference Nutrient Intake (RNI) for vitamin B12 is set by SACN (1991). Values are micrograms per day.

Vitamin B12 deficiency is often missed because the symptoms develop slowly and look like ordinary tiredness at first. The classic signs are:

• Persistent, unusual tiredness and lack of energy
• Breathlessness on light exertion
• Headaches
• Pale or slightly yellow-tinged skin
• A sore, red, smooth tongue (glossitis)
• Mouth ulcers
• Pins and needles, or numbness, especially in the hands and feet
• Difficulty walking or balancing
• Disturbed vision (rarely)
• Changes in mood, memory, or thinking (irritability, low mood, confusion)
• In children: poor growth and slowed development

The crucial point: the nervous system symptoms can develop even before the anaemia is detectable on a routine blood test. Pins and needles, balance problems, and noticeable changes in memory or mood, particularly in a high-risk group, are reason enough to see a GP and ask about B12.

Who is at higher risk in the UK

• Vegans. The single largest predictable risk group. B12 is not naturally in any plant food; fortified products and a supplement together solve it.
• Strict vegetarians. Possible risk if eggs and dairy intake is also low.
• Adults aged 50 and over. Stomach acid production falls with age, and so does B12 absorption from food.
• People on long-term proton pump inhibitors (PPIs) or H2 blockers (for acid reflux): reduced stomach acid means reduced B12 absorption.
• People on metformin long-term (for type 2 diabetes): some reduction in B12 absorption is well documented.
• People with pernicious anaemia. An autoimmune condition that damages the intrinsic-factor mechanism the gut uses to absorb B12. Treated with regular B12 injections.
• People with coeliac disease, Crohn's disease, or after gastric surgery. Absorption is reduced.
• Heavy alcohol use. Affects absorption and storage.

When to see your GP: any of the neurological symptoms above (pins and needles, balance changes, memory or mood changes), particularly in a risk group, or persistent unexplained fatigue. A blood test for B12 and folate is the standard first step. Confirmed deficiency is treated with B12 injections (for absorption problems) or oral high-dose B12 (for dietary deficiency).

Vitamin B12 from food is not a risk. Excess B12 is excreted in the urine.

NHS supplement guidance: taking 2mg (2,000 micrograms) or less a day of B12 in supplements is unlikely to cause harm.

Most over-the-counter UK B12 supplements deliver between 10 and 1,000 micrograms per tablet, far below the 2mg upper level. The doses sometimes used for confirmed deficiency (1,000 to 2,000 micrograms a day) are safe for short courses and are commonly prescribed.

There is no documented risk of long-term harm from B12 supplementation at the doses sold in the UK. Some people report mild skin reactions or temporary mild diarrhoea at higher doses; these settle on stopping.

B12 is a special case in UK supplement guidance because it has a sharply defined risk group (people who do not eat animal foods, or who absorb less because of age, medication, or gut condition).

Who should consider a supplement

• Vegans. A daily 10 to 50 microgram supplement, or a 1,000 microgram supplement twice a week, is the typical recommendation. The Vegan Society's standard guidance is consistent with NHS advice and is a useful practical reference.
• Strict vegetarians with low intake of dairy and eggs. Same logic, lower dose.
• Adults aged 50 and over, particularly if on long-term PPIs or metformin. Discuss with GP; routine blood test for B12 status is reasonable.
• People with pernicious anaemia. Treated by GP with regular B12 injections; this is a medical regimen, not a do-it-yourself supplement.
• Pregnant or breastfeeding vegans. Continue a daily B12 supplement throughout. The increased requirement during breastfeeding (2.0 micrograms a day) is comfortably covered by typical UK vegan supplements.

Who probably does not need a supplement

• People who regularly eat meat, fish, eggs, or dairy and have no symptoms or risk factors.

What about B12 in plant foods that "sound like sources"?

• Spirulina, chlorella, fermented soya, raw sea vegetables: these contain B12-like analogues that are largely biologically inactive in humans. They are not a reliable source. Do not rely on them in place of fortified foods or a supplement.

• Whole article on plant-based diets, with B12 covered at length: Plant-based eating.
• The other nutrient behind anaemia: Iron. B12 deficiency anaemia and iron deficiency anaemia share symptoms but have very different causes; a blood test distinguishes them.
• Best food sources: Mussels, Mackerel, Beef, Eggs, Milk.

• NHS. Vitamins and minerals: Vitamins B. nhs.uk/conditions/vitamins-and-minerals/vitamin-b. Adult RNI, food sources, and supplement guidance.
• NHS. Vitamin B12 or folate deficiency anaemia. Symptoms, causes, diagnosis, treatment.
• SACN. Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. Department of Health Report 41 (1991).
• NHS. The vegan diet. Includes the standing advice on B12 supplementation.
• Public Health England. McCance and Widdowson's The Composition of Foods, 7th summary edition (2015).
• USDA Agricultural Research Service. FoodData Central, SR Legacy release. fdc.nal.usda.gov.

This page is reference information for UK shoppers. It is not medical advice. Suspected B12 deficiency should be investigated with a blood test ordered by a GP.