Vitamins · 4 min read ·

Vitamin B12: vegans cannot do without it

Vitamin B12 is found almost only in animal foods. Vegans and people on some medicines are often short of it — and it is absorbed in a more complicated way than other vitamins.

B12

In a nutshell

1What it does and how much you need

Vitamin B12 (cobalamin) is needed by two enzymes: one breaks down certain fatty acids and amino acids, the other converts homocysteine into methionine together with folate. A deficiency causes anaemia with large red blood cells and nerve damage.1

EFSA recommendation 4 µg EFSA set the adequate intake at 4 µg a day for adults, 4.5 µg in pregnancy and 5 µg when breastfeeding. At this intake, people’s blood markers of B12 tend to be normal.1

2Where to find it

Data 59 µg Vitamin B12 is found almost only in animal foods. A hundred grams of beef liver contain 59 µg, herring 14 µg, sardines 9 µg, mackerel 8.7 µg, beef tenderloin 3.5 µg and Emmental 3.1 µg.2
Moderate evidence — a review up to 62% A review of 18 studies: B12 deficiency or depleted stores were found in 62% of pregnant vegetarians, 25–86% of children, 21–41% of adolescents and 11–90% of older vegetarians. It occurred regardless of age, place of residence or type of vegetarian diet.3

3How it is absorbed

Vitamin B12 first has to be released from proteins in food, then binds to the so-called intrinsic factor from the stomach, and only with it is it absorbed at the end of the small intestine. EFSA assumes that about 40% is absorbed from food.1

Moderate evidence — a large study +65% People who took stomach acid-lowering drugs (proton pump inhibitors) for 2 years or more had a 65% higher risk of B12 deficiency.4
Moderate evidence — a randomised trial 19% vs 10% In a trial of people taking metformin to prevent diabetes, 19% had low or borderline B12 after 5 years, compared with 10% on placebo. Each year of use raised the risk of deficiency by 13%.5

4Forms and doses

In the EU, supplements may contain vitamin B12 as cyanocobalamin, hydroxocobalamin, adenosylcobalamin or methylcobalamin.6

Moderate evidence — a review the same pathway A review of how cells process vitamin B12: methylcobalamin and adenosylcobalamin go through the same pathway in the body as cyanocobalamin, so an advantage is unlikely.7
Weak evidence — Cochrane 1,000 µg A Cochrane review: a 1,000 µg tablet a day corrected B12 levels much like an injection and cost less. But the evidence is of low quality, from 3 small studies.8
Weak evidence — a small study 500 µg A 500 µg tablet raised B12 just as much whether people let it dissolve under the tongue or swallowed it.9
Weak evidence — a randomised trial 647–1,032 µg In older people with mild B12 deficiency, status was corrected only by 647–1,032 µg of cyanocobalamin a day — more than 200 times the usual recommended amount.10

What to take from this

Sources

Written on , based on studies available at that date. Newer research may change the conclusions.

  1. EFSA NDA Panel (2015). Scientific Opinion on Dietary Reference Values for cobalamin (vitamin B12). EFSA Journal 13:4150. doi.org/10.2903/j.efsa.2015.4150
  2. USDA ARS (2018). FoodData Central — SR Legacy, vitamin B12 per 100 g: beef liver, raw 59.3 µg (FDC 169451), herring, raw 13.7 µg (FDC 175116), sardines in oil, drained 8.9 µg (FDC 175139), mackerel, raw 8.7 µg (FDC 175119), beef tenderloin, raw 3.5 µg (FDC 171767), swiss cheese (Emmental) 3.1 µg (FDC 171251). fdc.nal.usda.gov
  3. Pawlak R. et al. (2013). How prevalent is vitamin B12 deficiency among vegetarians? Nutr Rev 71:110–117. doi.org/10.1111/nure.12001
  4. Lam J. R. et al. (2013). Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA 310:2435–2442. doi.org/10.1001/jama.2013.280490
  5. Aroda V. R. et al. (2016). Long-term metformin use and vitamin B12 deficiency in the Diabetes Prevention Program Outcomes Study. J Clin Endocrinol Metab 101:1754–1761. doi.org/10.1210/jc.2015-3754
  6. Directive 2002/46/EC on food supplements, Annex II — forms of vitamins and minerals permitted in supplements (consolidated version 26 Nov 2025). eur-lex.europa.eu
  7. Obeid R., Fedosov S. N., Nexo E. (2015). Cobalamin coenzyme forms are not likely to be superior to cyano- and hydroxyl-cobalamin in prevention or treatment of cobalamin deficiency. Mol Nutr Food Res 59:1364–1372. doi.org/10.1002/mnfr.201500019
  8. Wang H. et al. (2018). Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. Cochrane Database Syst Rev CD004655. doi.org/10.1002/14651858.CD004655.pub3
  9. Sharabi A. et al. (2003). Replacement therapy for vitamin B12 deficiency: comparison between the sublingual and oral route. Br J Clin Pharmacol 56:635–638. doi.org/10.1046/j.1365-2125.2003.01907.x
  10. Eussen S. J. et al. (2005). Oral cyanocobalamin supplementation in older people with vitamin B12 deficiency: a dose-finding trial. Arch Intern Med 165:1167–1172. doi.org/10.1001/archinte.165.10.1167

This is general information and does not replace a doctor. Food supplements are not medicines; buy them from trusted sellers and talk to a doctor if you are ill or take medicines.