Vitamin B12 (cobalamin) is involved in cell division, red blood cell formation, energy metabolism, and normal nervous system function – the body cannot produce it itself and relies on intake via food or supplements. The problem: significant, reliably usable amounts are provided almost exclusively by animal-based foods. Those who follow a vegan or highly restrictive diet, who are older, take acid blockers or metformin, or have a gastrointestinal condition are at an increased risk of deficiency. This article analyzes what the DGE reference values, EFSA claims, and current specialist literature actually say about symptoms, testing methods, dosage, and the much-discussed question of algae as a B12 source.

What is vitamin B12 and what does the body need it for?

Vitamin B12, also known as cobalamin, is a water-soluble vitamin that, unlike most other water-soluble vitamins, can be stored in significant quantities in the liver – storage reserves often last for several years in healthy adults. This explains why a deficiency often only becomes apparent gradually and with a significant delay. In metabolism, B12 acts as a coenzyme in two central reactions: the breakdown of homocysteine into methionine and the conversion of methylmalonyl-CoA, an intermediate product of fatty acid and amino acid breakdown. Through these reactions, vitamin B12 is involved in the formation of myelin, the insulating protective layer around nerve fibers, as well as in blood formation and cell division. Naturally occurring in significant, reliably bioavailable amounts, B12 is found almost exclusively in animal products; plant-based foods normally only contain it following bacterial fermentation.

An overview of the 8 EFSA-authorized functions of vitamin B12

The European Food Safety Authority (EFSA) has established a list of authorized health claims based on Regulation (EU) No. 432/2012. A total of eight claims are authorized for vitamin B12 – more than for any other micronutrient already covered in this guide.

These statements are legally permitted, EFSA-validated claims regarding normal function – they are not medicinal claims and do not make statements about treating or preventing diseases. Phrases like "more energy" or "better mental performance" go beyond the authorized wording and are not permitted.

How does a vitamin B12 deficiency manifest? An overview of symptoms

Because the liver can store B12 for years, a deficiency usually develops gradually and is often noticed only late. Early signs are frequently non-specific and are easily attributed to other causes: fatigue, difficulty concentrating, memory weakness, headaches, as well as increased irritability or depressive moods. If the deficiency remains untreated, two groups of symptoms can develop, which overlap in the advanced stage:

• Hematological signs (blood formation): A disruption in red blood cell formation leads to megaloblastic anemia, characterized by abnormally large but too few red blood cells. Typical consequences are paleness, shortness of breath under exertion, heart palpitations, and general weakness.
• Neurological and psychological signs: Tingling or numbness in the hands and feet, instability when walking, muscle weakness, visual disturbances, and – in the case of a very pronounced, long-standing deficiency – memory impairment, potentially leading to an increased risk of cognitive decline. Other possible signs include hair loss and inflammation of the oral and tongue mucosa (glossitis).

Important context: Unlike changes in blood counts, neurological damage can only recover slowly or incompletely in advanced, long-standing cases. The earlier a deficiency is detected and treated, the better the prognosis. For persistent, unexplained complaints from the list above, medical evaluation is the most sensible first step rather than self-diagnosing or taking high doses.

Who is at an increased risk for a vitamin B12 deficiency?

Since reliably bioavailable B12 is found almost exclusively in animal foods, diet is the most important risk factor. Other risk groups arise from conditions or medications that disrupt absorption in the gastrointestinal tract:

• Vegans and those following highly restrictive vegetarian diets: without targeted supplementation or fortified foods, there is a high risk of insufficient intake.
• Older people: With increasing age, the production of gastric acid and intrinsic factor decreases; the latter is a protein essential for the absorption of B12 in the small intestine.
• People who take acid blockers: Proton pump inhibitors like omeprazole or pantoprazole, as well as H2 blockers, reduce gastric acid production and thus the release of B12 from food.
• People who take metformin: The medication frequently prescribed for diabetes mellitus can inhibit the absorption of cobalamin in the intestine.
• People with stomach or intestinal diseases: such as chronic gastritis (especially the autoimmune form), Crohn's disease, ulcerative colitis, or conditions following stomach or intestinal surgeries such as bariatric surgery.
• People with chronic alcohol consumption: due to both insufficient intake and alcohol-induced impaired absorption.

Anyone in these groups usually benefits from regular monitoring of their B12 status rather than uncontrolled self-supplementation at unknown levels.

Vitamin B12 and women: pregnancy, breastfeeding, and trying to conceive

Vitamin B12 deficiency during pregnancy is not a minor footnote but a topic with direct relevance for the unborn child. Maternal deficiency is associated with an increased risk of neural tube defects, miscarriages, and premature births. Children exposed to a severe deficiency in the womb may exhibit neurological abnormalities after birth, such as apathy, irritability, excessive crying, or feeding difficulties. Vegan women are particularly affected: according to studies, the average daily B12 intake for a strict vegan diet is only about 0.4 µg – significantly below the requirement for pregnant women of 4.5 µg per day. Women who want to conceive and follow a vegan or predominantly plant-based diet should therefore speak with their gynecologist at an early stage, ideally before pregnancy, to have their B12 blood levels checked rather than addressing the issue only after becoming pregnant. The specific treatment of a diagnosed deficiency, such as dosage and form of administration, belongs in medical hands.

Vitamin B12 daily requirement: An overview of DGE reference values

The German Nutrition Society (DGE) revised its reference values for vitamin B12 in 2019 and increased the estimated value for adults from the previous 3.0 µg to 4.0 µg per day. Because requirements cannot be determined with the previously customary precision, the DGE no longer lists the values as fixed intake recommendations, but rather as estimates for an adequate intake.

For comparison: According to the National Nutrition Survey, the average actual intake for women in Germany is about 3.8 µg and for men about 5.3 µg per day – meaning for women, it is on average just below the new estimate. However, these average values do not provide information about individual nutritional status, especially in the case of vegan diets or the risk factors mentioned above.

How is a vitamin B12 deficiency detected?

A deficiency cannot be reliably identified by individual symptoms, as these are non-specific and can have many other causes. Only a blood test provides reliable information. The classic total B12 value in serum is only of limited significance: laboratory experts point out that a functional deficiency can exist even with a measured value of 400 ng/l. More sensitive modern markers include holotranscobalamin (Holo-TC), which measures the early available, active fraction of B12, and methylmalonic acid (MMA), which accumulates in the blood or urine during a B12 deficiency.

These values are provided for classification purposes and do not replace a medical diagnosis. If a deficiency is reasonably suspected, your GP or specialist practice is the right point of contact for the appropriate combination of tests and interpretation.

The best sources of vitamin B12: foods compared

Rich sources of B12 are almost exclusively animal-based foods, primarily liver, but also muscle meat, eggs, milk, cheese, and fish. As a rough guide, dairy products, meat, cold cuts, eggs, as well as fish and seafood containing more than 1.2 µg of B12 per 100 grams are considered particularly rich sources. In practice, the daily requirement of a healthy adult can be met, for example, by a combination such as 150 g of yogurt, a glass of milk, an egg, and 100 g of mozzarella, or likewise by a beef steak (100 g) or a salmon fillet served with 100 g of quark. Plant-based foods generally only contain significant amounts of B12 after bacterial fermentation, such as in sauerkraut, although these amounts are variable and usually significantly lower than in animal sources.

The big myth: can algae or spirulina provide vitamin B12?

Spirulina, chlorella, and other algae supplements are often advertised as plant-based sources of B12 – the data on this is much more cautious than marketing texts suggest. While some bacteria and algae can produce B12-like compounds, according to the Max Rubner Institute, these are mostly so-called pseudovitamins – cobalamin analogues that cannot be used by human metabolism like true B12 and can even block the absorption of true B12. Dietary supplements based on such algae are therefore generally not a suitable source of B12. An exception is Chlorella vulgaris: although this microalga does not produce B12 itself, it can absorb and enrich a form that is bioavailable to humans from its environment. A Finnish study found that vegans who consumed chlorella and/or the macroalga nori over a longer period of time had B12 blood levels about twice as high as vegans who did not consume algae. Anyone wishing to rely on algae products as a B12 source should therefore specifically look for tested Chlorella vulgaris supplements and regularly monitor their success through a blood test instead of relying on general marketing claims about "algae" or "spirulina".

Can you overdose on vitamin B12? Safety and limits

Compared to many other micronutrients, vitamin B12 is considered relatively well-tolerated, as excess amounts are largely excreted by the kidneys and the body's absorption capacity decreases as the dose increases. Nevertheless, the German Federal Institute for Risk Assessment (BfR) warns against uncontrolled high-dose intake and suggests a maximum daily amount of 25 µg for dietary supplements. This does not contradict the fact that, depending on the cause, significantly higher doses may be used in the medical treatment of a diagnosed, severe deficiency—for example, orally in three-digit microgram amounts or, in the case of impaired intestinal absorption, via injection at intervals of several months. However, such high-dose, therapeutic applications belong in medical hands, are based on an individual diagnosis, and are not comparable to preventive self-supplementation without a diagnosed need. For general, non-medically supervised supplementation, the following applies: follow the daily portion recommended by the BfR instead of the significantly higher, sometimes four-digit microgram dosages of some over-the-counter preparations, just because they are advertised as "safe because water-soluble".

How is a deficiency treated? Nutrition, supplements, or injections?

The appropriate treatment depends on the cause and extent of the deficiency and should be determined by a doctor. In the case of a purely diet-related, mild insufficiency, an adjustment of food choices or oral supplementation is often sufficient. If the cause lies in impaired absorption, for example due to a lack of intrinsic factor in autoimmune gastritis, oral supplementation alone may not be enough – in these cases, medically prescribed, high-dose injections are used to bypass the impaired intestinal absorption. VEYT does not offer injectable preparations and does not replace medical treatment for a diagnosed deficiency; daily B12 supplementation is intended for people who want to support their basic supply as part of a healthy, balanced diet.

Supplementing vitamin B12 sensibly in everyday life

Those who wish to support their daily B12 supply as part of a balanced diet can find vitamin B12 at VEYT in the Daily Essentials Complete multivitamin complex – combined with over 20 other vitamins and minerals, including iron, zinc, magnesium, and vitamin D3, in practical softgel capsules.

As with all VEYT products: GDPR-compliant ordering, fast shipping within Germany, transparent return policies, and secure payment methods via PayPal, Klarna, or credit card.

Frequently asked questions about vitamin B12

Sources: German Nutrition Society (DGE) – Vitamin B12 Reference Values, Regulation (EU) No 432/2012 – List of permitted health claims, Specialist Society for Nutritional Therapy and Prevention (FETeV) – Vitamin B12, Federal Institute for Risk Assessment (BfR) – Maximum amount proposals for vitamin B12, Consumer Association – Vitamin B12 against exhaustion and fatigue, t-online / dpa – Vegan and pregnant: preventing vitamin B12 deficiency in the child. This article does not replace individual medical advice.