Vitamin B12 is easy to get from meat, fish, eggs and dairy, and hard to get from plants. This guide covers how much you need, which foods supply it, the symptoms of deficiency, and who should think about a supplement. Figures come from the NIH Office of Dietary Supplements, Vitamin B12 fact sheet.
If you eat plant-based, our plant protein vs whey guide covers the protein side of the same choice.
Quick Answer: How Much B12 Do You Need?
Adults need 2.4 mcg of vitamin B12 a day, and the best sources are animal foods. Plant foods do not naturally contain B12, so vegans and many vegetarians rely on fortified foods or supplements.
What Vitamin B12 Does
Vitamin B12 is required for the development, myelination and function of the central nervous system, for healthy red blood cell formation, and for DNA synthesis. It is a water-soluble vitamin, and compounds with B12 activity are called cobalamins because they contain cobalt.
B12 is often sold as an energy booster. The NIH reports that supplementation does not appear to improve athletic performance or endurance in people with sufficient B12 status. Trials in older adults also found no improvement in cognitive function from B12 supplements, with or without folic acid or B6. A supplement helps when you are short of B12, and not otherwise.
How Much B12 You Need
- Adults and teens aged 14 and over. 2.4 mcg a day.
- Pregnancy. 2.6 mcg a day.
- Breastfeeding. 2.8 mcg a day.
- Children. 0.9 mcg at 1 to 3 years, 1.2 mcg at 4 to 8 years and 1.8 mcg at 9 to 13 years.
The body stores about 1 to 5 mg of B12, which is roughly 1,000 to 2,000 times the amount most people eat in a day. Deficiency can therefore take several years to show up.
How B12 Is Absorbed
In food, B12 is bound to protein. Stomach acid and digestive enzymes release it, and it then binds to intrinsic factor, a protein made by cells in the stomach lining. The B12-intrinsic factor complex is absorbed in the last part of the small intestine.
B12 added to fortified foods and supplements is already in free form, so it skips the release step. Absorption falls sharply once a single dose exceeds what intrinsic factor can carry, at about 1 to 2 mcg. The NIH estimates B12 from supplements is absorbed about 50% better than B12 from food.
Vitamin B12 Deficiency Symptoms
- Blood. Megaloblastic anaemia, where red blood cells are abnormally large, plus low counts of white and red blood cells.
- Nerves. Numbness and tingling in the hands and feet. These symptoms can occur without anaemia, so early diagnosis matters to avoid irreversible damage.
- General. Fatigue, palpitations, pale skin, weight loss and a sore tongue (glossitis).
- Other. Dementia and infertility have been reported in severe deficiency.
Most laboratories treat a serum B12 below 200 to 250 pg/mL as subnormal, and a doctor may check methylmalonic acid to confirm. See a doctor if you have these symptoms, since many other conditions cause fatigue, including low iron. Our iron-rich foods guide covers that side.
Who Is at Risk of Deficiency
- Older adults. Between 3% and 43% of community-dwelling older adults are deficient depending on the definition, partly because atrophic gastritis affects 8% to 9% of adults aged 65 and over and lowers intrinsic factor and stomach acid.
- Pernicious anaemia. An autoimmune disease that stops the stomach producing intrinsic factor, so B12 is not absorbed even with a good diet.
- Digestive conditions and gut surgery. Including coeliac disease.
- Vegetarians and vegans. Natural sources are limited to animal foods.
- Some medicines. Acid-reducing drugs such as proton pump inhibitors and H2 blockers can interfere with absorption from food, and metformin might reduce absorption.
Best Food Sources of B12
Amounts per serving, from the NIH food table, against a daily need of 2.4 mcg:
- Beef liver, 3 oz cooked. 70.7 mcg.
- Clams, 3 oz cooked. 17 mcg.
- Oysters, 3 oz cooked. 14.9 mcg.
- Salmon, 3 oz cooked. 2.6 mcg.
- Canned light tuna, 3 oz. 2.5 mcg.
- Ground beef, 3 oz. 2.4 mcg.
- Milk, 1 cup (2%). 1.3 mcg.
- Plain fat-free yogurt, 6 oz. 1.0 mcg.
- 1 large egg. 0.5 mcg. See our guide to protein in an egg.
The NIH notes B12 from dairy appears to be about three times better absorbed than from meat, fish and poultry. Fruit, vegetables, beans and wholegrain bread contain none.
Vegetarian and Vegan B12 Sources
Vegetarians who eat dairy and eggs can reach the target with ordinary foods. A cup of milk, a pot of yogurt and an egg add up to about 2.8 mcg using the NIH values.
Vegans need fortified foods or a supplement. Fortified nutritional yeast gives 8.3 to 24 mcg per quarter cup depending on the brand, and fortified breakfast cereals are another high-bioavailability source, with amounts that depend on the label (a cereal fortified to 25% of the Daily Value gives 0.6 mcg per serving). Tempeh, often listed as a B12 source, gives only 0.1 mcg per half cup.
For a plant-based breakfast idea, try one of our high protein breakfast smoothies and check any fortified ingredient label for its B12 content.
B12 Supplements
Consider talking to your doctor about a supplement if you are vegan, are older, have pernicious anaemia or a digestive condition, have had stomach or gut surgery, or take metformin or acid-reducing medicine.
- Cyanocobalamin. The most common supplement form. Methylcobalamin, adenosylcobalamin and hydroxycobalamin are also used.
- Sublingual tablets and lozenges. Evidence suggests they work no better or worse than swallowed tablets.
- Injections. Prescribed for deficiency from pernicious anaemia and other conditions that block absorption.
Safety and Side Effects
No upper intake level has been set for B12 because its potential for toxicity is low. Some observational studies link very high blood levels to cancer risk, while other evidence shows no link, so the NIH says more research is needed.
If you are pregnant or breastfeeding, have a medical condition, or take medicine, ask your doctor before starting a supplement. Do not treat symptoms such as numbness or persistent fatigue with supplements before a blood test.
Frequently Asked Questions
How much vitamin B12 do I need per day?
Adults and teens aged 14 and over need 2.4 mcg a day. The recommended amount rises to 2.6 mcg in pregnancy and 2.8 mcg while breastfeeding.
Can vegans get enough B12 without a supplement?
Plant foods do not naturally contain B12. Fortified breakfast cereals and fortified nutritional yeast are reliable sources with high bioavailability, and the NIH notes that fortified foods and supplements can substantially reduce the risk of deficiency. Check the label, because B12 content varies by brand.
Does vitamin B12 give you energy?
Only if you are short of it. Fatigue is a symptom of deficiency, but the NIH reports that B12 supplements do not appear to improve athletic performance or endurance in people who already have enough.
How long does it take to become B12 deficient?
Often several years. The body stores about 1 to 5 mg of B12, roughly 1,000 to 2,000 times the amount most people eat in a day, so symptoms can take years to appear.
Can you take too much vitamin B12?
No upper limit has been set for B12 because its potential for toxicity is low, and it is generally considered safe even at high doses. Observational evidence on very high blood levels and cancer risk is mixed, and the NIH says more research is needed.
Do sublingual B12 tablets work better than regular ones?
Evidence suggests no difference in efficacy between oral and sublingual forms. Injections are prescribed for deficiency caused by pernicious anaemia or other conditions that block absorption.
The Bottom Line
Adults need 2.4 mcg of B12 a day, and meat, fish, eggs and dairy supply it easily. Vegans need fortified foods or a supplement, and older adults, people with absorption problems and people on metformin or acid-reducing medicine are also at higher risk.
B12 helps when you are short of it and does little otherwise. If you have symptoms or belong to a risk group, ask your doctor for a blood test.
This article is for general information and is not medical advice.
