Vitamin B12, also called cobalamin, is a water-soluble vitamin that has a key role in the normal functioning of the brain and nervous system via the synthesis of myelin (myelinogenesis), and the formation of red blood cells. After the body uses these vitamins, leftover amounts leave the body through the urine.
The body can store vitamin B12 for years in the liver.
Animals store vitamin B12 in liver and muscle and some pass the vitamin into their eggs and milk; meat, liver, eggs and milk are therefore sources of the vitamin for other animals, including people. For humans, the bioavailability from eggs is less than 9%, compared to 40% to 60% from fish, fowl and meat. Insects are a source of B12 for animals (including other insects and humans).
Animal sources with a significant content of vitamin B12 (range among top 20 sources of 50 to 99 µg per 100 grams) include clams, organ meats (especially liver) from lamb, veal, beef, and turkey, fish eggs, mackerel, and crab meat.
B12 is produced in nature only by prokaryotes in the form of certain bacteria and archaea; it is not made by any multicellular or single-celled eukaryotes. It is synthesized by some gut bacteria in humans and other animals, but humans cannot absorb the B12 made in their guts, as it is made in the colon which is too far from the small intestine, where absorption of B12 occurs.Ruminants, such as cows and sheep, absorb B12 produced by bacteria in their guts. For gut bacteria of ruminants to produce B12 the animal must consume sufficient amounts of cobalt.
Grazing animals pick up B12 and bacteria that produce it from the soil at the roots of the plants they eat.
Feces is a rich source of vitamin B12 and many species, including rabbits, dogs, and cats eat feces.
Fortified foods and supplements
The UK Vegan Society, the Vegetarian Resource Group, and the Physicians Committee for Responsible Medicine, among others, recommend that every vegan who is not consuming adequate B12 from fortified foods take supplements.
Foods for which B12-fortified versions are widely available include breakfast cereals, soy products, energy bars, and nutritional yeast.
Vitamin B12 or B9 (commonly called folate) deficiency anaemia occurs when a lack of vitamin B12 or folate causes the body to produce abnormally large red blood cells that can't function properly.
Symptoms of vitamin B12 or folate deficiency
Vitamin B12 and folate perform several important functions in the body, including keeping the nervous system healthy.
A deficiency in either of these vitamins can cause a wide range of problems, including:
a lack of energy
pins and needles (paraesthesia)
a sore and red tongue
psychological problems, which may include depression and confusion
problems with memory, understanding and judgement
Some of these problems can also occur if you have a deficiency in vitamin B12 or folate, but don't have anaemia.