Vitamin B12
Vitamin B12 (cobalamin) is the vitamin that keeps nerves and red blood cells healthy. Adults need about 2.4 mcg a day, and it occurs naturally only in animal foods, so vegans rely on fortified foods or supplements.
2.4 µga day for adults, US RDA
2.5 µg on EU food labels (NRV), the figure behind label percentages
Upper limit · none set; no harm shown from high intakes
- Most per 100 g 90µg Lamb liver
- Most per portion 8.2µg 1 can sardines
- Main sources Fish, meat and shellfish then eggs and dairy; plants none unless fortified
- From a supplement ~10µg absorbed from a 500 mcg tablet
Daily amount: the US RDA for adults aged 19 and over (NIH). Food figures per 100 g from USDA FoodData Central; fortified breakfast cereal is left out of the ranking.
Foods High in Vitamin B12
Ranked per 100 g, with what a usual portion gives, limited to 3 foods per category. Foods with a Caltide calorie page link to it.
L
Lamb liver
26 µg in 1 oz
90µg / 100 g
C
Caviar
3.2 µg in 1 tablespoon
20µg / 100 g
O
Octopus
17 µg in 3 oz
20µg / 100 g
C
Chicken liver
19 µg in 4 oz
16.6µg / 100 g
H
Herring
25 µg in 1 fillet
13.7µg / 100 g
C
Chicken heart
7.3µg / 100 g
R
Rabbit
2 µg in 1 oz
7.2µg / 100 g
V
Venison
1.8 µg in 1 oz
6.3µg / 100 g
O
Ostrich
7.7 µg in 1 cup
5.7µg / 100 g
D
Duck egg
3.8 µg in 1 egg
5.4µg / 100 g
G
Goose egg
7.3 µg in 1 egg
5.1µg / 100 g
S
Swiss cheese
0.66 µg in 1 slice
3µg / 100 g
Per 100 g vs. a Usual Portion
Why the food that ranks first per 100 g can give less in a real serving.
| Food | Usual portion | Per 100 g | Per portion |
|---|---|---|---|
| Sardines | 1 can (92 g) | 8.9µg | 8.2µg |
| Salmon | 1 fillet (125 g) | 3.9µg | 4.8µg |
| Tuna | 1 can (107 g) | 2.6µg | 2.7µg |
| Beef mince | 1 patty (85 g) | 2.8µg | 2.4µg |
| Egg | 1 egg (50 g) | 1.1µg | 0.56µg |
| Milk | 1 cup (236 g) | 0.56µg | 1.3µg |
One portion of sardines covers about 3.4 times the 2.4 mcg adults need a day. Small amounts in many animal foods add up fast, so for people who eat them a shortage is more often a problem of absorption than of diet.
What Is Vitamin B12?
Vitamin B12 is the largest and most complex vitamin, built around an atom of cobalt, which is where the name cobalamin comes from. Only microbes, certain bacteria, can make it. Animals take it up from bacteria and store it, which is why it reaches people through meat, fish, eggs and milk.
In the body it works with two enzymes. One, methionine synthase, recycles homocysteine into methionine and keeps folate in a usable form for making DNA. The other, methylmalonyl-CoA mutase, helps break down some fats and amino acids for energy. Together they explain the two classic signs of a shortage: large, misshapen red blood cells and damage to nerves.
How the Body Absorbs Vitamin B12
Food B12 is bound to protein. Stomach acid and enzymes free it; it then binds intrinsic factor, a protein made by the stomach lining; and the pair is absorbed at the end of the small intestine. A failure at any step causes a shortage even on a diet full of B12. That is what happens in pernicious anemia, an autoimmune disease that destroys the cells making intrinsic factor.
Intrinsic factor can handle only about 1 to 2 mcg at a meal. Above that, roughly 1% of a dose slips in by passive diffusion. So a 500 mcg tablet delivers about 10 mcg: about 98% is lost, yet what remains is still four times the daily need. That is why high-dose tablets work even for some people who absorb poorly.
Vitamin B12 in a Day of Food With Fish
One ordinary day built only from foods in the Caltide food library, in usual portions. No supplements. Bread and potato, like all unfortified plant foods, give none.
| Meal | Food | Amount | Vitamin B12 |
|---|---|---|---|
| Breakfast | Egg | 50g | 0.56µg |
| Breakfast | Milk | 236g | 1.3µg |
| Snack | Greek yogurt | 150g | 1.1µg |
| Lunch | Tuna | 107g | 2.7µg |
| Lunch | Bread | 24g | 0µg |
| Dinner | Salmon | 125g | 4.8µg |
| Dinner | Potato | 200g | 0µg |
| Total | 10µg |
Signs of Low Vitamin B12
The liver holds a large store, so a shortage can take years to show after intake falls. Early signs are tiredness and weakness from anemia, loss of appetite and weight loss. Nerve signs include numbness or tingling in the hands and feet, trouble with balance, confusion, memory problems, depression and a sore mouth or tongue. Nerve damage can become permanent if the shortage goes on.
A large intake of folic acid can hide the anemia while the nerve damage carries on, which is why folate and B12 are best checked together. The anemia itself can look like iron deficiency at first glance, but the red blood cells are large instead of small.
Who Is Most Likely to Be Low in Vitamin B12
- Vegans and many vegetariansplant foods have none unless fortified; eggs and dairy help but may not cover the need
- Adults over 50less stomach acid frees less B12 from food; the B12 in supplements and fortified foods is not bound to protein
- After stomach or bowel surgeryweight-loss surgery and removal of part of the small intestine cut absorption
- Long-term metformin or acid reducersboth are linked with lower B12 levels over years of use
Vitamin B12 Supplement Forms
Supplements and fortified foods are also a source of vitamin B12, and for vegans the main one. Four forms are sold; all of them are cobalamin with a different group attached to the cobalt.
- Cyanocobalaminthe most common and most studied form, used in most multivitamins and fortified foods; the body converts it to the active forms
- Methylcobalaminone of the two forms active in the body; studies have not shown it to be clearly better absorbed than cyanocobalamin
- Adenosylcobalaminthe other form active in the body, also sold as a supplement
- Hydroxocobalaminalso given by injection to treat pernicious anemia and severe deficiency
Tablets that dissolve under the tongue have not been shown to work better than ones you swallow.
Sources: NIH Office of Dietary Supplements, EFSA, US National Academies. Not medical advice.
Vitamin B12 in Caltide
- Logged automaticallyCaltide adds up the vitamin B12 in every food you log from the food library and shows it against the amount for your age and sex in the Nutrition tab.
- Supplements count tooAdd your B12 tablet once with its micrograms as an ingredient. Each day you tick it off, it counts toward your total. The figure is the dose on the label, not the smaller amount you absorb.
Vitamin B12 Sources and References
The figures and claims on this page are checked against these sources. Food amounts come from USDA FoodData Central.
Questions About Vitamin B12
Adults need 2.4 mcg a day in the US, 2.6 mcg in pregnancy and 2.8 mcg while breastfeeding. The EU label reference is 2.5 mcg, and EFSA sets an adequate intake of 4 mcg.
In the Caltide food library, lamb liver: 90 mcg per 100 g, then Caviar (20 mcg) and Octopus (20 mcg). Liver and shellfish such as clams are among the richest sources.
Yes, or fortified foods eaten every day. Vitamin B12 occurs naturally only in animal foods, so a vegan diet without fortified foods or supplements supplies almost none.
Many make less stomach acid with age, and stomach acid is what frees B12 from the protein in food. The US National Academies advise adults over 50 to get most of their B12 from supplements or fortified foods, where it is not bound to protein.
Only a small share of a large dose. In healthy people, about 10 mcg of a 500 mcg tablet is absorbed. Intrinsic factor, the protein that carries B12 into the gut wall, takes up only about 1 to 2 mcg per meal; beyond that, only about 1% of the dose gets in by passive diffusion.
Studies have not shown that one is clearly better absorbed or used. Cyanocobalamin is the most common and most studied form, and the body turns it into methylcobalamin and adenosylcobalamin, the two active forms.
No upper limit has been set, by the US or by EFSA, because no harm has been shown from high intakes in healthy people. What the gut does not absorb is lost.
Metformin, the diabetes drug, and acid reducers taken for years, such as proton pump inhibitors (omeprazole, lansoprazole) and H2 blockers, can lower absorption. People on them long term may want their B12 checked.
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