What is vitamin B12? Vitamin B12 is absolutely crucial for our cells, for blood formation, our brain, and much more. Nevertheless, we often don’t notice that our reserves are slowly depleting for years. The good news is that you can monitor your vitamin B12 levels regularly and react to a deficiency early by adjusting your diet or supplement intake.
A lack of vitamin B12 is commonly considered a typical vegan disorder – but it does not only affect vegans. One thing is for certain: This B vitamin is mainly found in animal foods. Anyone who follows a vegan diet is strongly advised to do so with vitamin B12 supplements. But even some vegetarians and meat-eaters lack vitamin B12. Really large amounts are mainly found in offal and fish – that is, in foods that are not always a favorite dish for many. People also at risk of vitamin B12 deficiency also includes pregnant women, the elderly, people with pancreatitis, and type 2 diabetes.
If you want to find out more about vitamin B12 foods, supplements, causes of vitamin B12 deficiency, and how to treat a deficiency, keep reading our blog article. You’ll also find out which people are more at risk of developing a vitamin B12 deficiency over the course of their lifetime.
What Is Vitamin B12?
Vitamin B12 is an essential vitamin. This means that your body cannot produce it itself, and you have to consume it through food. Like the other B vitamins, it is also a water-soluble vitamin. Water-soluble vitamins are regularly excreted through the kidneys and urine. As a rule, they have to be continually consumed because the body cannot store them. Studies have however shown that your body can store vitamin B12 in the liver for two to six years.
This is why vitamin B12 is also known as cobalamin because its chemical structure contains the heavy metal cobalt. The biochemically active forms of vitamin B12 that are effective in the body are methylcobalamin and 5-adenosylcobalamin.
Vitamin B12 is very sensitive to air and light. When you prepare a meal – for example, by cooking, foods will lose about 12 percent of their vitamin B12 content on average.
What Effect Does Vitamin B Have on the Body?
Vitamin B12 plays an important role in numerous metabolic processes. It is involved in folate metabolism, blood formation, and the breakdown of fatty acids, among other things.
Additional central metabolic processes that involve vitamin B12 include:
- DNA formation
- Nerve protection and regeneration
- Cell division and respiration
Are Folic Acid and Vitamin B12 the Same Thing?
Like vitamin B12, folic acid belongs to the group of B vitamins. Previous names for folic acid were vitamin B9 and B11. A vitamin B12 deficiency causes a folic acid deficiency because the body needs vitamin B12 to convert folic acid into its active form. Among other things, a folic acid deficiency can lead to anemia and increase the risk of cardiovascular disease. But be careful – an excess of folic acid can lead to a vitamin B12 deficiency.[3–6]
Does Vitamin B12 Affect Blood Clotting?
Vitamin B12 plays an important role in blood formation. It ensures the maturation process of the red blood cells, the erythrocytes. The vitamin is involved in the formation of DNA and in cell division and thus stimulates the production of red blood cells.[3–5]
How Does B12 Affect the Nervous System?
Vitamin B12 is also known as the neuro vitamin. It is responsible for the production of the myelin sheath, which surrounds the nerve cells as a membrane. Myelin protects the cells and supports the transmission of signals from cell to cell.
How Do I Consume Vitamin B12?
In order for vitamin B12 to perform its important functions in the body, it must be consumed via food or dietary supplements.
How Does My Body Use Vitamin B12?
Vitamin B12, which you ingest through your diet, first enters the stomach. There, the stomach acid releases it and binds it to certain proteins. In the intestine, the mucous membrane of the small intestine can then absorb the vitamin and pass it on to the blood. Transport proteins, the transcobalamins, then transport vitamin B12 into all cells of the body and into the liver.
If there are insufficient important transport proteins – for example, due to a genetic defect – vitamin B12 cannot be distributed correctly in the body. This is one possible cause of a vitamin B12 deficiency.[4, 8, 9]
In order for vitamin B12 intake to be effective, the stomach, pancreas, and intestines must function well. If the function of one of these organs is impaired, this can lead to a vitamin B12 deficiency. The following diseases worsen the absorption of vitamin B12:[3, 12, 14]
- gastritis, inflammation of the gastric mucosa
- damage to the mucous membrane of the small intestine, such as Crohn’s disease
- pancreatitis, inflammation of the pancreas
Did you know that about two to five micrograms of vitamin B12 are stored in the body? Half of them are found in the liver and can remain there for almost three years.[4, 8]
What Are Foods High in B12?
Vitamin B12 sources include mainly animal foods such as meat, fish, eggs, and milk. Algae is discussed as a vegan alternative. So far, however, researchers have only found a form of the vitamin in so-called nori algae, which humans may be able to absorb – however, the amounts are too small and not everyone is able to absorb this form of the vitamin. Vegans, therefore, are advised to consume vitamin B12 supplements or foods enriched with vitamin B12 – for example, juices – in order to meet their needs.
The following table provides an overview of foods high in B12. According to the German Nutrition Society, each adult should consume four micrograms of vitamin B12 on a daily basis.[11–13]
Vitamin B12 Sources (Micrograms per 100 Grams)
Meat and Fish
Beef liver – 91 µg
Swiss cheese – 3.1 µg
Veal liver – 60 µg
Camembert – 2.6 µg
Pork liver – 39 µg
Edam – 1.9 µg
Beef kidney – 33 µg
Cottage cheese – 2.0 µg
Mackerel – 9 µg
Chicken egg – 1.9 µg
Herring – 8.5 µg
Quark – 0.8 µg
Salmon – 4.7 µg
Full-fat milk – 0.4 µg
Tuna – 4.3 µg
Cream – 0.4 µg
Lamb – 2.7 µg
Yogurt – 0.4 µg
Beef tenderloin – 2.0 µg
Salami – 1.4 µg
Ham – 0.6 µg
Turkey breast – 0.5 µg
Did you know that an overdose of vitamin B12 is almost impossible if you consume it naturally through your diet? The body normally excretes excess vitamin B12 via the kidneys and urine. Only when you take high doses of vitamin B12 over a long period of time is it possible for the kidneys to be overwhelmed.
How Much B12 Do You Need a Day?
In order for vitamin B12 to perform all its functions in the body, we need to ingest it through food. At the beginning of 2019, the German Nutrition Society (DGE) significantly increased its recommendations for the daily intake of vitamin B12. It now recommends a daily intake of four micrograms for adolescents aged 13 and over and adults. The requirement for children depends on their age – for example, 0.5 micrograms for infants up to the age of four months and 3.5 micrograms for children between 10 and 13. Pregnant women need 3.5 micrograms, while breastfeeding women need 4 micrograms per day.
For more information about supplements and your diet during pregnancy and breastfeeding, visit our Health Portal article.
The US National Institutes of Health (NIH) recommends values that are significantly lower than the more recent recommendations of the DGE. For example, a daily intake of 2.4 micrograms of vitamin B12 should be guaranteed for adolescents aged 14 and over and adults. Pregnant women, on the other hand, should consume 2.6 micrograms per day, and breastfeeding women need 2.8 micrograms.
Recommendations for the daily intake of vitamin B12 (in micrograms, µg):
0.5 to 3.5 µg
0.4 to 1.8 µg
4 µg (after 13 years of age)
2.4 µg (after 14 years of age)
Can the Body Produce Its Own Vitamin B12?
Some animals, especially cows, can produce vitamin B12 themselves. Numerous bacteria live in their rumen and produce vitamin B12 from food, which is then absorbed into the bloodstream. This is also the reason why beef contains vitamin B12.
Can the human body also produce vitamin B12? Scientists are still discussing this. The intestinal bacteria in our digestive system can probably produce vitamin B12, but they do so in the wrong place – namely, in the colon. However, vitamin B12 is absorbed into the bloodstream in the small intestine. Therefore, the vitamin produced does not enter into the blood or liver. Instead, it is excreted through our stool. Whether the body’s own production of vitamin B12 contributes our vitamin B12 levels is still a topic of debate.
Did you know that some vegetarian mammals do not get enough vitamin B12 from their regular diet? Among others, guinea pigs and rats have found an extremely unappetizing solution – they eat their feces, which contains vitamin B12 produced in the colon.
How Vitamin B12 Deficiency Occurs
Vitamin B12 deficiency is a widespread problem. Studies have shown that around six percent of people up to the age of 60 in the United States and United Kingdom are deficient in vitamin B12.
Many of these people with vitamin B12 deficiency are probably not even aware that they lack this important vitamin. A vitamin B12 deficiency can usually go unnoticed for a long time. Since the liver stores the vitamin, it can take years for you to experience symptoms. The downside of this is that while B12 reserves are secretly emptied, serious long-term health problems can occur, such as anemia, nerve damage, and reduced vision.[1, 3, 4]
What Are the Causes of a Vitamin B12 Deficiency?
Vitamin B12 deficiency can affect anyone. Those who have an unhealthy and unbalanced diet may not get enough vitamin B12 and develop a deficiency in the long run. There are some risk groups that are frequently affected:
- Vegans and vegetarians
- Older people
- Pregnant and breastfeeding women
- People after a stomach operation
- People with chronic pancreatitis or type 2 diabetes
- Chronically stressed people
Vegetarian and Vegan Diets
A common cause of vitamin B12 deficiency is a vegan or vegetarian diet. Vitamin B12 is found almost exclusively in animal foods, and vegans can only satisfy their vitamin B12 needs with dietary supplements. Vegetarians, on the other hand, can fall back on cheese, milk, eggs, and curd. However, these foods contain significantly lower amounts of vitamin B12 than meat and fish – even a vegetarian can be at a higher risk of developing a vitamin B12 deficiency.
Researchers are currently investigating whether the demand could be met by plant-based foods such as mushrooms and algae. Certain algae, for example, contain vitamin B12, but research has shown that they do so in forms that our bodies cannot utilize. The same may be true for shiitake mushrooms, but studies are still ongoing.[21, 22]
Nutrition is probably also a reason behind the differing vitamin B12 levels in men and women. A study by the American Society for Microbiology showed that men consume animal products such as meat more often than women. And according to the National Consumption Study II, men consume vitamin B12 more frequently than women.[22, 23]
Does B12 Deficiency Get Worse over Time?
Age is also a risk factor. This is partly due to the fact that older people often suffer from chronic illnesses, take various medications, and that their eating habits change with age.[24, 25] In addition, older people produce less gastric acid. However, stomach acid is necessary to release vitamin B12 from food so that it can later be absorbed into the blood.
Vitamin B12 Deficiency in Pregnant and Breastfeeding Women
Pregnant and breastfeeding women not only have to provide themselves with vitamin B12 – their growing baby also needs this vitamin. As a result, they need to increase their daily intake and should absolutely avoid developing a vitamin B12 deficiency. Vitamin B12 levels play a decisive role in the physical and mental development of unborn and newborn children. In the worst case, extreme vitamin B12 deficiency during pregnancy can even lead to miscarriage.
How Do Illness and Surgery Affect Vitamin B12 Deficiency?
People who suffer from pancreatitis, an inflammation of the pancreas, often suffer from a lack of vitamin B12. They lack the enzyme trypsin, which is necessary for vitamin B12 uptake.
Studies have also shown that people with type 2 diabetes who take the drug metformin often have difficulties with their vitamin B12 levels. It appears that metformin interferes with the absorption of the vitamin.
You should also ensure that you receive vitamin B12 via dietary supplements after surgical gastric removal. The stomach plays a decisive role in the utilization of vitamin B12; after removal or reduction, absorption is often impaired.
Symptoms and Consequences of Vitamin B12 Deficiency
The symptoms of vitamin B12 deficiency are varied and often generic, making it difficult to detect.
What Are the Symptoms of Vitamin B12 Deficiency?
Vitamin B12 is involved in numerous metabolic processes in the body and thus provides us with energy, among other things. A vitamin B12 deficiency impairs mental and physical performance and therefore leads to less energy or fatigue. The following symptoms can also occur:
- Fatigue and exhaustion
- Headaches and difficulty concentrating
- Digestive problems
Even if none of the above symptoms are present, an extreme vitamin B12 deficiency can have health consequences if it remains undetected or untreated for a long time.
Is There a Link between Vitamin B12 Deficiency and Anemia?
If the body lacks sufficient vitamin B12, cell division in the bone marrow is disrupted. As a result, fewer red blood cells can be produced there. This can lead to pernicious anemia, a special form of anemia. This anemia is accompanied by paleness, fatigue, reduced performance, and concentration.
Does B12 Deficiency Cause Low Oxygen?
A vitamin B12 deficiency also impairs the transportation of oxygen around the body. Vitamin B12 helps to build iron into the blood – iron, in turn, transports oxygen through the body. Insufficient oxygen in our bodies can lead to decreased performance and concentration, immunodeficiency, exhaustion, and fatigue.[1, 26]
Neurological Disorders and Depression
Vitamin B12 is responsible for protecting neurons. If the vitamin cannot fulfill this function due to a deficiency, fewer nerve fibres are formed in the spinal cord. This can lead to neurological symptoms such as:
- Nervousness and irritability
- Pain, numbness, or tingling in hands, arms, feet, and legs
Scientists are still researching the exact connections between vitamin B12, folic acid, and depression. A common theory is based on the amino acid homocysteine. If there is not enough vitamin B12 in the body, there is too much homocysteine. An excess of this amino acid can damage the tissue in the brain and disrupt signal transmission. This, in turn, leads to mood swings and depression.
It is also being investigated whether supplements containing vitamin B12, folic acid and vitamin B6 can relieve depressive symptoms. The results are not yet clear. Some researchers recommend taking folic acid (800 micrograms per day) and vitamin B12 (1 milligram per day) to support depression treatment.[32, 33]
Can Vitamin B12 Deficiency Cause Dementia?
The symptoms of a pronounced vitamin B12 deficiency are similar to those of other neurological diseases – pain and numbness, for example, can also occur in herniated discs. This is another reason why vitamin B12 deficiency is often diagnosed very late.
Over time, vitamin B12 deficiency can cause damage from impaired nerve cells and anemia – and may increase the risk of developing Alzheimer’s disease. The medical links between this illness and a vitamin B12 deficiency have not yet been clarified, and studies have so far failed to produce consistent results. However, there are indications that an optimal supply of B vitamins and folic acid can contribute to optimal mental health in old age.
Alzheimer’s disease is a brain disorder that almost always occurs in people over the age of 60. According to one study, it affects 14 percent of people over 70 and 37 percent of people over 90. Alzheimer’s disease mainly affects memory, orientation, and speech, as well as personality changes.
Vitamin B12 Deficiency and Cardiovascular Diseases
Vitamin B12 deficiency may contribute to the development of cardiovascular diseases such as cardiac insufficiency, stroke, and heart attack.
What does vitamin B12 have in common with the cardiovascular system? It is primarily the amino acid homocysteine. Vitamin B12 breaks down homocysteine and converts it into other substances that contribute to folic acid metabolism. If your body does not have enough vitamin B12 available, it breaks down less homocysteine. The concentration of the amino acid increases – and with it, the risk of arteriosclerosis – that is, the calcification and narrowing of the blood vessels. This is one of the strongest risk factors for heart attack, stroke, and other cardiovascular diseases.
Did you know that cardiovascular diseases are responsible for one-third of deaths worldwide – and the trend is rising.
Are There Other Possible Causes of a Vitamin B12 Deficiency?
Reduced vision may also be a sign of vitamin B12 deficiency. The connection between vitamin B12 and certain messenger substances and hormones can also lead to psychological disorders such as depression and psychosis. If there is a lack of vitamin B12, this can disrupt energy metabolism, which can lead to muscle weakness, exhaustion, fatigue, and lack of concentration. A deficiency can also manifest itself in digestive disorders such as loss of appetite, diarrhea, constipation, and inflammation in the mouth, stomach, and intestines.
How Do I Test My Vitamin B12 Levels?
A blood test can tell you more about your vitamin B12 levels. Various levels can be measured. Holo-Transcobalamin (Holo-TC) is a particularly useful parameter, by which you can check your vitamin B12 levels. Holo-Transcobalamin is the transport form of vitamin B12, which binds to proteins in the blood. It is the only form that can be absorbed by all cells of the body. A low Holo-TC level is an early warning sign of a vitamin B12 deficiency.
How Can I Check My B12 Level at Home?
You can have a vitamin B12 test performed by a doctor, of course. Another alternative that you test your vitamin B12 levels at home, with an at-home vitamin B12 test kit.
For the test, you collect a few drops of blood yourself with a finger prick and send your blood sample to a specialist laboratory. After it has been analyzed, you will usually receive your results with your Holo-Transcobalamin levels – you might even receive recommendations on steps you can take to improve your vitamin B12 levels.
What Is the Best Treatment for B12 Deficiency?
If you are aware that you are deficient in vitamin B12, you have to boost your vitamin B12 levels. Which steps you should take depends on the extent of the deficiency. If you suffer from a severe deficiency, you should consult a doctor to check whether the deficiency has possible consequences for your health.
Generally, there are three different ways to improve vitamin B12 levels:
- Deliberately include more vitamin B12-rich foods in your diet
- Use vitamin B12 supplements in the form of tablets, capsules, or drops
- Get injections of high-dose vitamin B12 administered to you
What Are Good Vitamin B12 Sources?
Vitamin B12 from food is found exclusively in animal foods. If you are an adult and are not breastfeeding, you can meet your daily requirements with 100 grams of tuna, 150 grams of lamb or 100 grams of salmon. Vegetarian alternatives are 200 grams of cottage cheese or two chicken eggs.
When heating foods high in B12, however, keep in mind that vitamin B12 can be lost depending on how you prepare your food. The vitamin is very sensitive to heat and light. Heat can destroy the vitamin, so roasting or cooking reduces the vitamin B12 content of food.
When Would I Receive Vitamin B12 Injections?
Vitamin B12 can also be injected into the muscle. These injections are very high doses. Physicians generally administer them to quickly replenish empty vitamin B12 reserves. In this case, you will usually receive an injection once a month. Vitamin B12 injections are particularly suitable for people suffering from digestive disorders, which means that not enough vitamin B12 enters the bloodstream from the stomach.
Treating Vitamin B12 Deficiency with Supplements
In order to compensate for a vitamin B12 deficiency, you can consume high-dose vitamin B12 supplements. These dietary supplements are usually available in the form of capsules or drops and are often vegan.
Good vitamin B12 supplements contain the vitamin in one of its active forms, methylcobalamin or adenosylcobalamin. These supplements boast high bioavailability, meaning the body can use the supplement quickly and effectively.[3, 36]
Supplements should not contain any additives that could interfere with the action of the vitamin. Combining supplement intake with substances that promote absorption is recommended. Vitamin B12 works well with other B vitamins and folic acid.
How Do I Consume Vitamin B12 Supplements?
According to various health authorities and studies, an amount of 500 to 2,000 micrograms of vitamin B12 per day is recommended. It is not possible to say exactly how much you will need to raise your levels. This varies depending on how optimal your vitamin B12 levels are. For example, you might want to consider taking a dose of 1,000 micrograms daily at first, then weekly, and then monthly once your vitamin levels are optimal again.[36, 37]
Can I Supplement Vitamin B12 with Toothpaste?
One of many important vitamin B12 sources is, believe it or not, toothpaste. According to new studies toothpaste enriched with vitamin B12 was able to improve the B12 values of study participants. The vitamin is absorbed through the oral mucosa during the act of brushing teeth. This is great for people whose digestive tract is unhealthy and who cannot effectively absorb supplements in drop or capsule form.[39, 40]
What Should I Know about Zinc and Vitamin B12 tablets?
You should only consume zinc supplements if you have a zinc deficiency. Otherwise, you run the risk of developing zinc poisoning. Compounds such as zinc histidine, gluconate and bisglycinate are most suitable. It is not recommended to take high amounts of medications or other minerals at the same time. The administration should be discussed with a doctor.
Can I Overdose on Vitamin B12?
So far, there have been no reports of anyone overdosing on vitamin B12. The body can usually simply excrete excess water-soluble vitamins via the kidneys. However, when taking dietary supplements, follow your doctor’s recommendations or instructions. It is best to perform a vitamin B12 test to find out if you need to boost your levels.
What Is Vitamin B12 – at a Glance
What Is Vitamin B12?
Vitamin B12 is a water-soluble vitamin that you need to consume through your diet or dietary supplements.
What Effect Does Vitamin B12 Have on the Body?
The main tasks of the vitamin include blood formation, protecting neurons, cell division and supporting folic acid metabolism.
How Do I Ensure That I Receive Enough Vitamin B12?
Good vitamin B12 sources are predominantly animal foods. Whether you can also meet your needs with plant-based foods such as algae or fungi needs to be investigated further. Pregnant women, breastfeeding mothers, the elderly, and people with gastrointestinal diseases need more vitamin B12.
What Are Vitamin B12 Deficiency Causes?
Frequently, a vegan, vegetarian, or simply unbalanced diet leads to a deficiency. Other causes are drugs that inhibit gastric acid, certain diseases such as diabetes and pancreatitis and genetic metabolic disorders.
What Are Vitamin B12 Deficiency Symptoms?
Vitamin B12 deficiency is associated with depression, digestive problems, anemia, poor concentration, and neurological disorders. A severe deficiency can reduce performance and promote the development of cardiovascular disease and dementia.
How Can I Treat Vitamin B12 Deficiency?
If you confirm you have a deficiency – for example, through a blood test – you can take countermeasures with a targeted diet consisting of foods high in B12 or take dietary supplements or injections.
- Folate, I. of M. (US) S.C. on the S.E. of D.R.I. and its P. on, Vitamins, O.B., Choline, A.: Estimation of the Period Covered by Vitamin B12 Stores. National Academies Press (US) (1998)
- W. Kaim, B. Schwedersk: Bioanorganische Chemie – Zur Funktion chemischer Elemente in Lebensprozessen. Teubner (2005)
- Die ganze Welt der Vitamine, Mineralstoffe und Enzyme. garant Verlag GmbH, Renningen (2016)
- Kasper, H., Burghardt, W.: Ernährungsmedizin und Diätetik. Elsevier, Urban & Fischer, München (2014)
- Arens-Azevêdo, U., Pletschen, R. und Schneider, G.: Ernährungslehre: zeitgemäß, praxisnah. Bildungsverlag EINS GmbH., Köln (2011)
- Vitamin B12 | DACH Liga Homocystein, http://www.dach-liga-homocystein.org/content/vitamin-b12
- Myelin, http://www.nationalmssociety.org/What-is-MS/Definition-of-MS/Myelin
- Froese, D.S., Gravel, R.A.: Genetic disorders of vitamin B12 metabolism: eight complementation groups – eight genes. Expert Rev Mol Med. 12, (2010). doi:10.1017/S1462399410001651
- Ärzteblatt, D.Ä.G., Redaktion Deutsches: Ursachen und frühzeitige Diagnostik von Vitamin-B12-Mangel, https://www.aerzteblatt.de/archiv/61696/Ursachen-und-fruehzeitige-Diagnostik-von-Vitamin-B12-Mangel
- Vitamin B12-Versorgung bei veganer Ernährung: So geht’s!, https://www.peta.de/b12#.WrPEPojwa72
- Deutsches Grünes Kreuz für Gesundheit e.V.: Vorkommen von Vitamin B12, https://dgk.de/gesundheit/mikronaehrstoffe/lexikon/vitamine/vitamin-b-12-cobalamin/vorkommen-von-vitamin-b12.html
- National Institutes of Health: Office of Dietary Supplements - Vitamin B12, https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/
- Deutsche Forschungsanstalt für Lebensmittelchemie: Der kleine Souci/Fachmann/Kraut. Lebensmitteltabelle für die Praxis. Wissenschaftliche VErlagsgesellschaft Stuttgart
- Vitamin B₁₂, https://www.dge.de/wissenschaft/referenzwerte/vitamin-b12/
- Institute of Medicine. Food and Nutrition Board: Dietary Reference Intakes: Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline, (1998)
- Kon, S. K.; Porter, J. W. G.: The intestinal synthesis of vitamins in the ruminant. Vitamins and hormones.
- Degnan, P.H., Taga, M.E., Goodman, A.L.: Vitamin B12 as a modulator of gut microbial ecology. Cell Metab. 20, 769–778 (2014). doi:10.1016/j.cmet.2014.10.002
- Rowley, C.A., Kendall, M.M.: To B12 or not to B12: Five questions on the role of cobalamin in host-microbial interactions. PLOS Pathogens. 15, e1007479 (2019). doi:10.1371/journal.ppat.1007479
- Allen, L.H.: How common is vitamin B-12 deficiency? Am J Clin Nutr. 89, 693S-696S (2009). doi:10.3945/ajcn.2008.26947A
- Elmadfa, I.: Ernährungslehre. Verlag Eugen Ulmer Stuttgart (2015)
- Watanabe, F., Yabuta, Y., Bito, T., Teng, F.: Vitamin B12-Containing Plant Food Sources for Vegetarians. Nutrients. 6, 1861–1873 (2014). doi:10.3390/nu6051861
- Watanabe, F.: Vitamin B12 sources and bioavailability. Exp. Biol. Med. (Maywood). 232, 1266–1274 (2007). doi:10.3181/0703-MR-67
- American Society for Microbiology, https://www.asm.org/index.php/component/content/article/114-unknown/unknown/4739-the-difference-in-eating-habits-between-men-and-women?highlight=YToyOntpOjA7czozOiJtZW4iO2k6MTtzOjQ6Im1lYXQiO30=
- Monate, * Alle Preise verstehen sich zzgl der gesetzlichen MwSt Mindestlaufzeit 12: Lebenseinstellung - Veganer in Deutschland 2017 | Statistik, https://de.statista.com/statistik/daten/studie/445155/umfrage/umfrage-in-deutschland-zur-anzahl-der-veganer/
- Nutrients | Free Full-Text | Prevalence and Predictors of Subclinical Micronutrient Deficiency in German Older Adults: Results from the Population-Based KORA-Age Study, http://www.mdpi.com/2072-6643/9/12/1276
- Nahrungsergänzung, https://www.bzfe.de/inhalt/pressemeldung-6785.html
- Office of Dietary Supplements - Vitamin B12, https://ods.od.nih.gov/factsheets/VitaminB12-Consumer/
- Körner, U.: Ernährungsberatung in Schwangerschaft und Stillzeit. MVZ-Medizinverlage Stuttgart
- Toskes, P.P., Deren, J.J., Conrad, M.E.: Trypsin-Like Nature of the Pancreatic Factor That Corrects Vitamin B12 Malabsorption Associated with Pancreatic Dysfunction. J Clin Invest. 52, 1660–1664 (1973)
- Ärzteblatt, D.Ä.G., Redaktion Deutsches: Vitamin-B12-Mangel durch Metformin, https://www.aerzteblatt.de/nachrichten/41325/Vitamin-B12-Mangel-durch-Metformin
- Symptoms, https://www.nhs.uk/conditions/vitamin-b12-or-folate-deficiency-anaemia/symptoms/
- Bhatia, P., Singh, N.: Homocysteine excess: delineating the possible mechanism of neurotoxicity and depression. Fundamental & Clinical Pharmacology. 29, 522–528 (2015). doi:10.1111/fcp.12145
- Lim, S.Y., Kim, E.J., Kim, A., Lee, H.J., Choi, H.J., Yang, S.J.: Nutritional Factors Affecting Mental Health. Clinical Nutrition Research. 5, 143–152 (2016). doi:10.7762/cnr.2016.5.3.143
- Coppen, A., Bolander-Gouaille, C.: Treatment of depression: time to consider folic acid and vitamin B12. J. Psychopharmacol. (Oxford). 19, 59–65 (2005). doi:10.1177/0269881105048899
- Das Wichtigste über die Alzheimer-Krankheit . DAlzG, https://www.deutsche-alzheimer.de/die-krankheit/die-alzheimer-krankheit.html
- Are You Vitamin B12 Deficient?, https://draxe.com/b12-injections/
- Butler, C.C., Vidal-Alaball, J., Cannings-John, R., McCaddon, A., Hood, K., Papaioannou, A., Mcdowell, I., Goringe, A.: Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency: a systematic review of randomized controlled trials. Fam Pract. 23, 279–285 (2006). doi:10.1093/fampra/cml008
- Vidal-Alaball, J., Butler, C.C., Cannings-John, R., Goringe, A., Hood, K., McCaddon, A., McDowell, I., Papaioannou, A.: Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. Cochrane Database Syst Rev. CD004655 (2005). doi:10.1002/14651858.CD004655.pub2
- Vitamin-B12-angereichertes Zahngel für Vegetarier - BZfE, https://www.bzfe.de/inhalt/vitamin-b12-angereichertes-zahngel-fuer-vegetarier-alternative-zu-nahrungsergaenzungen-29020.html
- Vegane Ernährung, https://www.ernaehrungs-umschau.de/print-artikel/11-07-2014-vegane-ernaehrung-teil-2/
- Read “Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B6, Folate, Vitamin B12, Pantothenic Acid, Biotin, and Choline” at NAP.edu.