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Vitamin B12: Forms, Absorption, Vegans and Who Needs It

Also known as cobalamin, cyanocobalamin, methylcobalamin, hydroxocobalamin, adenosylcobalamin, B12

Short answer

Vitamin B12 is a water-soluble vitamin the body uses to make red blood cells and DNA and to keep the nervous system working. It is found naturally only in animal foods, so vegans rely on fortified foods or supplements. Cyanocobalamin is the most common supplement form. Metformin and acid-reducing medicines can lower B12 absorption [1].

Last reviewed · 2 sources

What is Vitamin B12?

Vitamin B12 is a water-soluble vitamin that contains the mineral cobalt, so its forms are called cobalamins [1]. The body needs it to develop and run the central nervous system, form healthy red blood cells and make DNA [1]. In food, B12 is bound to protein; stomach acid and a protein called intrinsic factor are needed to absorb it [1]. The B12 in supplements and fortified foods is already in free form [1].

Forms of Vitamin B12 you'll see on labels

  • Cyanocobalamin

    The most common form in supplements. The body converts it to the active forms [1].

  • Methylcobalamin

    One of the two active forms in the body, also sold in supplements [1].

  • Adenosylcobalamin

    The other active form, also used in some supplements [1].

  • Hydroxocobalamin

    Used in some supplements and, with cyanocobalamin, in prescription injections [1].

  • Sublingual tablets or lozenges

    Dissolved under the tongue. Evidence suggests no difference in effect between oral and sublingual forms [1].

  • Injections and nasal gel (prescription)

    Injections are usually used to treat deficiency from pernicious anemia and other absorption problems [1].

How much Vitamin B12 do adults need?

NIH lists these Recommended Dietary Allowances (RDA) for adults 19+, in micrograms (mcg). Reference values, not a personal recommendation.

GroupAmount per day
Men 19+2.4 mcg
Women 19+2.4 mcg
Pregnancy2.6 mcg
Lactation2.8 mcg

Upper limit: No UL has been set, because vitamin B12 has a low potential for toxicity [1]. In the UK, the NHS says 2 mg (2,000 mcg) or less a day from supplements is unlikely to cause harm [2].

How Vitamin B12 appears on a label

B12 is listed in mcg. The Daily Value (DV) used for % DV is 2.4 mcg for adults and children 4 and older [1]. Multivitamins usually contain 5 to 25 mcg, B-complex products 50 to 500 mcg, and B12-only products often 500 to 1,000 mcg [1]. Very high % DV numbers are common because only a small share of a large dose is absorbed: about 2% of a 500 mcg dose [1].

When to take Vitamin B12

No official source names a best time of day to take vitamin B12 or says whether to take it with food. NIH notes that absorption drops sharply once a single dose goes above about 1 to 2 mcg [1].

What to keep apart from Vitamin B12

  • Metformin

    Metformin might reduce B12 absorption and lower blood B12 levels [1]. Ask your pharmacist or doctor.

  • Acid-reducing medicines (PPIs and H2 blockers)

    Medicines such as omeprazole, lansoprazole and cimetidine can interfere with B12 absorption from food and may lead to deficiency [1]. Ask your pharmacist.

  • Folic acid

    Folic acid doses above 1 mg can mask the signs of B12 deficiency, which can damage the nervous system if missed [2].

Foods that contain Vitamin B12

  • Beef liver
  • Clams and oysters
  • Fortified nutritional yeast
  • Salmon and tuna
  • Beef
  • Milk, yogurt and cheese
  • Eggs
  • Fortified breakfast cereals

Who should ask a doctor or pharmacist first

Talk to a doctor or pharmacist if you take metformin or acid-reducing medicines, follow a vegan or vegetarian diet, are an older adult, or have had stomach or weight-loss surgery [1]. The same applies if you have pernicious anemia, celiac disease or Crohn's disease, which affect B12 absorption [1]. Vegan mothers who breastfeed should ask too, since their babies can become deficient [1].

Keep Vitamin B12 in a routine that fits

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Vitamin B12: questions people ask

NIH says no evidence shows that absorption of B12 from supplements differs by form [1]. Cyanocobalamin is the most common form, and the body converts it to the active forms [1].

No upper limit has been set, because B12 has a low potential for toxicity [1]. The NHS says 2 mg or less a day from supplements is unlikely to cause harm [2].

NIH lists tiredness, pale skin, palpitations, a sore tongue (glossitis), weight loss, megaloblastic anemia, and numbness or tingling in the hands and feet [1]. Symptoms can take years to show because the body stores B12 [1]. Only a blood test and a doctor can confirm it.

B12 occurs naturally only in animal foods, so vegans and vegetarians have a higher risk of deficiency [1][2]. NIH says fortified foods, such as nutritional yeast, and B12 supplements can substantially reduce that risk [1].

Evidence suggests no difference in effect between oral and sublingual B12 [1].

Injections are usually used to treat deficiency because they bypass absorption problems [1]. A Cochrane review found low-quality evidence that very high oral doses raised blood B12 about as well as injections [1]. Your doctor decides which suits you.

Only a small part of a large dose is absorbed: about 2% of 500 mcg and 1.3% of 1,000 mcg [1].

NIH says metformin might reduce B12 absorption and significantly lower blood B12 levels [1]. Ask your doctor about checking your B12.

Sources

  1. Vitamin B12: Fact Sheet for Health Professionals — NIH Office of Dietary Supplements
  2. B vitamins and folic acid - Vitamins and minerals — NHS

Educational information, not medical advice. The amounts above are official reference values, not a recommendation for you. Check with your doctor or pharmacist before starting or changing supplements, especially if you take medication, are pregnant or have a health condition. Supin sells a subscription, not supplements. Last reviewed .

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