By Nikola · Precision Nutrition L1 · Updated 5 November 2026
Vitamin B12 (cobalamin) is the B vitamin your body needs to make red blood cells, keep the nervous system healthy and release energy from food, and its natural sources are animal foods only. EFSA sets an adequate intake of 4 µg a day for adults, 4.5 µg in pregnancy and 5 µg while breastfeeding. Fish, meat, eggs, milk and cheese provide it; plant foods do not, unless they are fortified. That is why vegans need fortified foods or a supplement, and why people over 50, or on metformin or stomach acid medicines, are worth a closer look.
What vitamin B12 does
The NHS lists four jobs: B12 helps the body make red blood cells, keeps the nervous system healthy, helps release energy from food and helps the body use folate. A lack of it causes megaloblastic anaemia, the same blood picture as folate deficiency, and nerve problems that can appear even without anaemia (NIH).
Absorption is the weak point. To absorb B12 from food, the stomach must release it with acid and then bind it to intrinsic factor, a protein made by the stomach lining. The NIH explains that absorption drops sharply once intrinsic factor is saturated, at about 1-2 µg. From supplements, about 50% is absorbed at doses under 1-2 µg, but only about 2% of a 500 µg dose and 1.3% of a 1,000 µg dose. In other words, a 500 µg tablet delivers around 10 µg, still more than the daily reference intake.
The EU allows these health claims for foods that are at least a source of vitamin B12 (Regulation (EU) 432/2012):
- “Vitamin B12 contributes to normal energy-yielding metabolism”
- “Vitamin B12 contributes to normal functioning of the nervous system”
- “Vitamin B12 contributes to normal homocysteine metabolism”
- “Vitamin B12 contributes to normal psychological function”
- “Vitamin B12 contributes to normal red blood cell formation”
- “Vitamin B12 contributes to the normal function of the immune system”
- “Vitamin B12 contributes to the reduction of tiredness and fatigue”
- “Vitamin B12 has a role in the process of cell division”
How much you need a day
| Group | EFSA adequate intake | EFSA upper limit | For reference: NIH RDA |
|---|---|---|---|
| Men | 4 µg | not set | 2.4 µg |
| Women | 4 µg | not set | 2.4 µg |
| Pregnancy | 4.5 µg | not set | 2.6 µg |
| Breastfeeding | 5 µg | not set | 2.8 µg |
| Infants 7-11 months | 1.5 µg | not set | – |
Sources: EFSA Dietary Reference Values for cobalamin (2015), EFSA overview of upper limits, NIH ODS. EFSA lists “no defined adverse effects” for B12, so no upper limit exists, and the US Food and Nutrition Board did not set one either because of its low potential for toxicity. The UK figure is lower, about 1.5 µg a day for adults (NHS); the NHS also says 2 mg or less a day from supplements is unlikely to cause harm, but advises against taking more than you need.
Best food sources
| Food | B12, 100 g | Portion | B12 per portion |
|---|---|---|---|
| Sardines, canned in oil, drained | 8.94 µg | 1 tin, 92 g | 8.2 µg |
| Atlantic mackerel, raw | 8.71 µg | 85 g | 7.4 µg |
| Atlantic salmon, farmed, raw | 3.23 µg | 85 g | 2.7 µg |
| Beef, ground, 80% lean, raw | 2.14 µg | 113 g | 2.4 µg |
| Light tuna, canned in water | 2.55 µg | 85 g | 2.2 µg |
| Whole milk | 0.45 µg | 1 cup, 244 g | 1.1 µg |
| Swiss cheese | 3.06 µg | 1 slice, 28 g | 0.9 µg |
| Plain whole-milk yogurt | 0.37 µg | 170 g | 0.6 µg |
| Feta cheese | 1.69 µg | 28 g | 0.5 µg |
| Egg, whole, raw | 0.89 µg | 1 large, 50 g | 0.4 µg |
Source: USDA FoodData Central, SR Legacy, checked 5 November 2026: sardines FDC 175139, mackerel FDC 175119, salmon FDC 175167, ground beef FDC 174036, light tuna FDC 173709, milk FDC 171265, Swiss cheese FDC 171251, yogurt FDC 171284, feta FDC 173420, egg FDC 171287. Portions are USDA household measures; values per portion are calculated and rounded. The NIH also lists beef liver (70.7 µg per 85 g, cooked) and clams (17 µg per 85 g, cooked) as the richest sources, and fortified nutritional yeast at 8.3-24 µg per serving.
One tin of sardines or 85 g of mackerel gives about two days of the EFSA 4 µg. A portion of salmon, canned tuna or beef gives half or more. Dairy and eggs add smaller amounts that build up over a day: a glass of milk, a pot of yogurt and a little feta come to about 2 µg. If you eat no animal foods at all, none of this applies: plant foods do not naturally contain B12 (NIH).
Deficiency: signs and who is at risk
The NIH describes tiredness, weakness and megaloblastic anaemia, plus numbness and tingling in the hands and feet; these nerve symptoms can occur without anaemia. The NHS adds a sore and red tongue, mouth ulcers, muscle weakness, problems with vision and psychological problems, from mild depression or anxiety to confusion and dementia. Some of the damage can become permanent if diagnosis is late, so the NHS advises seeing a GP if you suspect a deficiency.
- Vegans and vegetarians. Natural sources are limited to animal foods, so people who eat few or none have a higher risk; fortified foods and supplements can substantially reduce it (NIH). Babies of vegan mothers who are pregnant or breastfeeding may also not get enough, with signs such as failure to thrive and developmental delays.
- People over 50. Many older adults have too little stomach acid to free B12 from food, and atrophic gastritis affects 8-9% of adults aged 65 and over (NIH).
- Pernicious anaemia. An autoimmune disease in which the stomach stops making intrinsic factor. It causes deficiency even with a good diet and is the most common cause of B12 deficiency in the UK (NHS).
- Stomach or gut conditions and surgery, including coeliac disease, Crohn’s disease and some types of stomach or intestinal surgery (NIH).
- Long-term medicines: metformin, proton pump inhibitors and H2 blockers (see below).
Supplements: when they make sense
- Vegan diet. A reliable B12 source, fortified foods or a supplement, is part of a well-planned vegan diet, not an extra. The NHS names a vegan diet without supplements or fortified foods as one cause of deficiency.
- Over 50. The NIH advises people over 50 to get most of their B12 from fortified foods or supplements.
- Diagnosed deficiency or pernicious anaemia. Treatment is set by a doctor; the NHS says it is usually given by injection at first, then by tablets or regular injections depending on the cause.
Forms. Cyanocobalamin is the most common form in supplements; methylcobalamin, adenosylcobalamin and hydroxocobalamin are also sold, including as sublingual tablets. The NIH says research has not shown that any form is better than the others. For everyone else who eats fish, meat, eggs or dairy, food comes first.
Who should be careful
- People on metformin. It might reduce B12 absorption and significantly lower blood levels (NIH). Do not stop the medicine; ask your doctor whether B12 checks make sense for you.
- People on proton pump inhibitors or H2 blockers, such as omeprazole, lansoprazole or cimetidine. They can interfere with B12 absorption from food by slowing the release of stomach acid (NIH).
- Anyone taking high-dose folic acid. More than 1 mg of folic acid a day can mask the symptoms of B12 deficiency while nerve damage continues (NHS). If you are over 50 or eat no animal foods, a B12 check before high-dose folic acid is sensible.
- Pregnant and breastfeeding vegans, because their babies might also not get enough B12 (NIH).
FAQ
Who needs a vitamin B12 supplement?
Mainly vegans and people who eat very few animal foods, people over 50, people with pernicious anaemia or stomach and gut conditions, and some people on long-term metformin or acid-lowering medicines. The NIH advises people over 50 to get most of their B12 from fortified foods or supplements; for medical conditions, a doctor sets the dose.
Which is better, methylcobalamin or cyanocobalamin?
According to the NIH, research has not shown that any form of supplemental B12 is better than the others. Cyanocobalamin is the most common form; methylcobalamin, adenosylcobalamin and hydroxocobalamin are alternatives.
How much vitamin B12 do I need a day?
EFSA sets an adequate intake of 4 µg a day for adults, 4.5 µg in pregnancy and 5 µg while breastfeeding. The US RDA is 2.4 µg and the UK figure about 1.5 µg; no upper limit has been set.
Related entries and articles
- Sardines, mackerel and salmon
- Eggs and feta cheese
- Vitamin B9 (folate and folic acid) and iron
- Vegan diet: benefits and risks
- Mediterranean mackerel stew with tomatoes and olives
- Baked salmon with root vegetables
Sources
- USDA FoodData Central, SR Legacy: sardine, Atlantic, canned in oil (FDC 175139); mackerel, Atlantic, raw (FDC 175119); salmon, Atlantic, farmed, raw (FDC 175167); tuna, light, canned in water (FDC 173709). fdc.nal.usda.gov
- USDA FoodData Central, SR Legacy: beef, ground, 80% lean, raw (FDC 174036); egg, whole, raw (FDC 171287). fdc.nal.usda.gov
- USDA FoodData Central, SR Legacy: milk, whole (FDC 171265); cheese, Swiss (FDC 171251); yogurt, plain, whole milk (FDC 171284); cheese, feta (FDC 173420). fdc.nal.usda.gov
- EFSA NDA Panel (2015). Scientific Opinion on Dietary Reference Values for cobalamin (vitamin B12). EFSA Journal 4150. efsa.europa.eu
- EFSA: Overview on Tolerable Upper Intake Levels as derived by the SCF and the EFSA NDA Panel, version 11 (August 2025). efsa.europa.eu
- NIH Office of Dietary Supplements: Vitamin B12, Fact Sheet for Health Professionals. ods.od.nih.gov
- NIH Office of Dietary Supplements: Vitamin B12, Fact Sheet for Consumers. ods.od.nih.gov
- NHS: Vitamins and minerals – B vitamins and folic acid. nhs.uk
- NHS: Vitamin B12 or folate deficiency anaemia. nhs.uk
- Commission Regulation (EU) No 432/2012 – permitted health claims. legislation.gov.uk
This page is for information only and is not medical or dietary advice.
