Where does B12 come from?
Besvaret 27. oktober 2026
B12 is made by bacteria. Neither plants nor animals can make it themselves. We get it from animal foods because the animals got it, either from bacteria in their gut or through their feed.
In ruminants such as cows and sheep, bacteria in the rumen make the vitamin as the feed ferments. This takes enough cobalt in the feed, so dairy cows are recommended a cobalt supplement. Humans and most animals with a single stomach, such as pigs and chickens, cannot make it and need it ready-made from their food. B12 has been added to animal feed for decades. Pork today has about a third less B12 than in the early 1990s, most likely because pigs are no longer fed animal offal.
Plants do not contain B12 on their own, but some plant foods have it added, such as many breakfast cereals and nutritional yeasts. Seaweed and algae can contain B12 from microbes living on them, but the amount varies from batch to batch, so they are not a reliable source.
So the animals are a step that can be skipped. The Danish food authority advises vegans to take a 4 µg B12 supplement a day and vegetarians to take a daily supplement.
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- Gennemgang fra Universidad de León, 2020Samler mange studier · OversigtsartikelRelationship between Vitamin B12 and Cobalt Metabolism in Domestic Ruminant: An Update
- Kommentar fra Quadram Institute, 2023Overblik eller holdning · KommentarThe importance of vitamin B12 for individuals choosing plant-based diets
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