Professor of Physiology, University of the Balearic IslandsJosep A. Tur does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.Universitat de les Illes Balears provides funding as a member of The Conversation ES.The only natural source of vitamin B12, essential for the normal functioning of the brain and nervous system, DNA synthesis or the formation of red blood cells, are foods of animal origin.Precisely those who do without those who follow strictly vegetarian diets.In these cases, then, it is necessary to supplement the contribution of the vitamin in the daily menu with supplements.Because without vitamin B12, or with low levels of intake, the number of red blood cells in the blood decreases and a disease called megaloblastic anemia appears.It manifests with pale skin, palpitations, loss of appetite and weight, infertility and neuropathies.The deficiency of this compound produces many other symptoms: motor and sensory incoordination, sensation of numbness or tingling in the hands and feet, balance problems, depression, confusion, dementia, memory problems and ulcers in the mouth or tongue.And in babies, it affects their normal development and growth.Actually, vitamin B12 is produced by microorganisms, which are ingested by animals.Vegetables neither need nor incorporate it, with few exceptions.Therefore, we obtain it mainly by eating foods of animal origin.The main sources are the liver, kidney and brains of various animals, which provide between 50 and 100 micrograms of vitamin B12 per 100 grams of food;egg yolk, clams, oysters, crabs, sardines, salmon and chicken liver (5-50 micrograms of vitamin per 100 g);and meat, whole egg, cheese, cow's milk, cod, hake, sole and tuna (0.2-5 micrograms per 100 g).Culinary techniques and industrial processes can affect the vitamin B12 content of foods.For example, when you pasteurize milk for 2 or 3 seconds, 7% is lost;when boiled between 2 and 5 minutes, 30% disappears;and when sterilized at 120℃ for 13 minutes, up to 77% is lost.B12, bound to food proteins, is released by the action of two substances secreted by the stomach, hydrochloric acid and pepsin, and binds to R proteins in saliva and the stomach.Upon reaching the duodenum, this union is broken by secretions from the pancreas.Now free, the vitamin binds to a protein produced by the oxyntic or parietal cells of the stomach, called intrinsic factor.This process will allow it to be absorbed in the ileum, the final section of the small intestine.Of all the vitamin B12 that reaches the intestine, we only absorb between 1 and 2 micrograms, which is considered enough for an optimal daily intake.Up to 1,000 to 2,000 times this amount may accumulate in the liver, so deficiencies may take several years to manifest.The importance of the intrinsic factor in the assimilation of vitamin B12 by our body accounts for a disease called pernicious anemia.This autoimmune disease destroys the parietal cells of the stomach, which are responsible for generating both the aforementioned intrinsic factor and hydrochloric acid.Both are essential to separate vitamin B12 from food proteins and promote its absorption by the intestine.As we have pointed out, vegetarians and, more specifically, vegans or strict vegetarians, may not get enough vitamin B12.In addition, if pregnant and lactating women follow this type of diet, the deficit can be transferred to babies.Supplements can be obtained from fortified foods, especially from soy and cereals, although the offer is currently scarce.Vegetable smoothies, such as almond, soy, coconut, or oatmeal, are often fortified, as are cereals or yeast.Some presentations of kombucha fermented tea, produced by a symbiosis between yeast and bacteria, indicate on their label that they contain around 20% of the recommended daily value of vitamin B12.However, no studies have been published to support it, nor is there evidence that the vitamin present in this product is biologically active in humans.It has also been suggested that batabatacha, a fermented black tea of ​​Japanese origin, might contain biologically active vitamin B12.Unlike kombucha, which is made by fermenting the already prepared product, batabatacha undergoes this process when it is still a leaf.Unconventional sources of doubtful efficacy are edible plants that have been poorly washed, since they can incorporate remains of vitamin B12 from bacteria present in the soil.Certain insects, such as termites, also contain vitamins produced by bacteria in their intestines.Another supplement candidate, spirulina, actually contains pseudovitamin B12, which is biologically inactive in humans;there is no scientific evidence on its properties as a supplement.Years ago, a study showed that fresh marine algae such as susabi-nori (Porphyra yezoensis) are effective in rats deficient in this vitamin.Of chlorella, very popular as a dietary supplement, nothing has been proven.In general, the possibility that algae contain some active derivative of B12 still does not yield consensus results in the international scientific community.With regard to nutraceuticals, or supplements in pharmaceutical form, we can find the compound in multivitamin preparations, B complex supplements and supplements that only contain vitamin B12, mainly in the form of cyanocobalamin.It can also be obtained by taking sublingual tablets, which dissolve under the tongue, or through injections.In the latter case, it is only advisable to administer it in this way under medical prescription and to treat severe deficiencies.Finally, it is available by prescription as a gel that is sprayed into the nose, a method that has not been shown to be effective.No presentation is better than another, and the amount of vitamin B12 they offer is very variable.Some provide much higher doses than recommended, such as 500 or 1,000 micrograms, of which the body only absorbs a small percentage.These doses are considered harmless, although it is always a good idea to read the product information to find out how much vitamin B12 it contains.Industrial production is carried out through fermentation by microorganisms such as Streptomyces griseus, a bacterium that for many years was the commercial source of vitamin B12.It is also obtained from Pseudomonas denitrificans and Propiobacterium shermanii, mainly through genetically engineered strains.What did dinosaurs actually look like?— VictoryPolitics with Michelle Grattan Podcast — Australian Capital TerritoryOceanic Thinking—Brisbane, QueenslandA Chance for Change — VictoriaDesigning Regenerative Futures Studio—Online, New South WalesCopyright © 2010–2022, The Conversation Media Group Ltd