Vitamin B12 Deficiency: Symptoms, Daily Needs and Which Form of B12 to Take

A vitamin B12 deficiency usually starts very quietly, with tiredness, a weaker memory and trouble concentrating. The only way to really pin it down is in the lab. Your body needs B12 for making blood, for its nerves and for cell division, but it can't make it on its own. For adults, the German Nutrition Society (DGE) sets an estimated value of 4.0 µg a day, which is just four thousandths of a milligram. Vitamin B12 is only found in relevant amounts in animal foods. If you're vegan, there's no getting around a supplement.

The earlier you can make sense of a deficiency, the better. And because one package says 5 µg and the next one 1,000, we also did the math on how much B12 from a capsule actually reaches your body.

What are the signs of a vitamin B12 deficiency?

The DGE lists memory problems, fatigue, attention problems and depressive moods as the main consequences of a B12 deficiency, along with nerve disorders and anemia. That's how it appears in its questions and answers on vitamin B12. Of course, almost everyone recognizes themselves somewhere on that list, especially after a long winter.

Two laboratory physicians pointed out in the German medical journal Deutsches Ärzteblatt that the nerve signs of a B12 deficiency are nonspecific and can leave lasting damage if you wait too long. Their advice: if you suspect something, measure early rather than guessing from symptoms. On top of that, the body keeps a large B12 store. According to the DGE, signs of deficiency usually only appear after years of too little coming in. So if you still feel really good after a year of being vegan, that doesn't automatically mean you're on the safe side.

Of all things, a lot of folate from supplements can mask a deficiency. It improves the anemia while the nerves keep suffering. That's why the European Food Safety Authority (EFSA) has set a tolerable upper intake level (UL) of 1,000 µg a day for folate, more on that in folic acid and methylfolate. Persistent tiredness belongs in your doctor's office. Why it reveals so little on its own is something we've pulled together in the article on signs of a vitamin deficiency.

Which test shows a vitamin B12 deficiency?

The most telling is the combination of a status marker, meaning holotranscobalamin (holo-TC) or the B12 in your blood, and the functional marker methylmalonic acid (MMA). That's exactly what the DGE recommends, too: one functional marker together with one status marker.

Holo-TC, often called “active B12,” is the B12 in your blood that's on its way into the cells right now. It's the first thing to drop when less comes in. Methylmalonic acid is a substance your cells can only process further with B12. When the stores run low, it builds up and rises in the blood. According to Herrmann and Obeid, the classic B12 value, on the other hand, is a late and fairly insensitive marker. It can still look completely normal while the supply is already faltering. If holo-TC is low and MMA and homocysteine are raised, the deficiency has reached your metabolism, even if you don't feel anything yet.

Anyone in a risk group should have their levels checked every two to three years, as the two authors recommend. These values aren't part of a standard blood count, so you'll need to ask for them specifically at your doctor's office.

Who is most likely to run low on vitamin B12?

The people most often affected are those who eat vegan or almost no animal foods, older people, and anyone who takes certain medications for years. According to the DGE, if you eat a fully plant-based diet and don't supplement B12, you have a high risk of deficiency.

In older people, the cause can also be the stomach rather than the plate. For B12 to get from the gut into the blood, it needs a protein carrier called intrinsic factor. That's made in the cells of the stomach lining. According to the DGE, diseases of the stomach or gut and surgery there can therefore lead to a deficiency, no matter how much B12 is on your plate. In that case, treatment belongs in a doctor's hands.

Two groups of medications are well studied. The first are proton pump inhibitors, the common stomach acid blockers. In a large US analysis of almost 26,000 people with B12 deficiency and around 184,000 without, those who took them for two years or longer had a roughly 65% higher risk of B12 deficiency. The second is the diabetes drug metformin. In a long-term study of more than 2,000 adults at increased risk of diabetes, after five years 19.1% of those on metformin had low or borderline B12 levels, compared with 9.5% on placebo. The authors therefore recommend having levels checked regularly while on metformin.

How much vitamin B12 do you need per day?

According to the DGE, adults need around 4.0 µg of vitamin B12 a day, pregnant women 4.5 µg and breastfeeding women 5.5 µg. The DGE calls this an estimated value because the data isn't enough for a precise recommendation. It refers to everything that comes in from food and supplements combined.

EFSA arrives at the same value with its reference value for adequate intake. The percentage on a package, on the other hand, refers to the NRV (nutrient reference value), which the EU set for labeling in its food information regulation. For B12 that's 2.5 µg, considerably less than the DGE value. So with B12, 100% NRV doesn't yet cover the DGE's full estimated value.

How much B12 from a supplement actually gets absorbed?

Of small amounts of B12, the gut absorbs a large share, of large amounts only a tiny fraction. The reason, again, is intrinsic factor. This transport route is quickly maxed out, and of everything beyond that, only one to two percent makes it through the gut wall.

How much that matters is shown by a review from the universities of Ljubljana and Trieste. Of 1 µg, the body absorbs about half, from around 20 µg less than a tenth, and from 500 µg and up only about 1%. An Indian study tracked labeled B12 through the body. Of 2.5 µg, as much as about 63% was absorbed there, and the body lost only about 0.7 µg a day. With four to eleven people per measurement, the study was very small. But it fits well with the picture that small daily amounts are used well. From this, we did our own math on roughly how much gets absorbed at different amounts:

At 5 µg, the lower bound is the amount already absorbed from 2.5 µg. The upper bound is the amount at a steady 63%. That means 5 µg a day covers the daily losses of around 0.7 µg 2.3 to 4.6 times over, on paper. A 500 µg tablet, on the other hand, doesn't get a hundred times as much into your body, only about one and a half to three times as much as 5 µg. Still, a lot of packages say 500 µg and more. It's different with a real deficiency, when empty stores need to be refilled quickly or the stomach isn't playing along. Then high doses or injections are a matter for your doctor.

For BASE by Fifty Five, we deliberately chose a moderate amount that keeps coming in every day. Our mini capsule contains 5 µg of methylcobalamin, the natural form of B12 your body uses. That's 200% NRV and 125% of the DGE estimated value, in an amount the gut can still absorb well every day, instead of a megadose where most of it never gets absorbed in the first place. Add to that all the other B vitamins, folate as methylfolate included.

Methylcobalamin or cyanocobalamin: which form is better?

For most people, all common forms of B12 are absorbed comparably well. Methylcobalamin is the form that also occurs in your body and in animal foods. Cyanocobalamin is more stable and cheaper, which is why it's in a lot of supplements. Both keep your B12 levels up well if you take them regularly.

The review from Ljubljana and Trieste considers the availability of all four forms comparable for the vast majority of the population. But it also collects hints that cyanocobalamin is retained slightly less well in tissue and excreted more. That's a small plus for the natural forms, though there's no clear winner. What happens inside the cell is described in a second review, whose co-author works for a food supplement manufacturer. According to it, every form is first broken down to the cobalamin core and then rebuilt into the two active forms. So methylcobalamin isn't “ready to go,” but it is the form your body already knows.

One small finding even points the other way. In a study of 42 vegans from Romania, the median holo-TC levels in the cyanocobalamin group were about twice as high as with methylcobalamin. The amounts weren't known, though, and nobody was randomized. Another finding was much clearer: everyone who regularly took a real B12 supplement was well supplied. The group relying on algae or kombucha, by contrast, had a median below the cutoff. We chose the natural form, but if you've been taking cyanocobalamin so far, there's no need to switch. How to spot good forms on the label is covered in the article multivitamin test: how to recognize quality.

Which foods contain vitamin B12?

According to the DGE, good sources of B12 are meat, fish and seafood, eggs and dairy products. Based on what we know today, a reliably sufficient intake from plant foods alone isn't possible.

Nori seaweed, shiitake mushrooms and products with cyanobacteria are often marketed as plant sources of B12. According to the DGE, though, the amounts they contain can vary enormously. And which form is in there and whether humans can even use it is often unclear. In the study of vegans above, it wasn't enough, either. So if you want to get B12 from your diet, you need animal or fortified foods. How vitamin B12 compares with the other vitamins and minerals is shown in our table of all vitamins and minerals.

Vegan B12: how much do you need, and how often?

According to the DGE, if you're vegan you should definitely take a B12 supplement, and do so permanently. It doesn't name a fixed daily dose, though. In its new position on vegan diets from 2024, it calls supplementation “absolutely necessary” for vitamin B12 as the only nutrient.

That sounds stricter than it is. In the same paper, the DGE for the first time considers a vegan diet health-promoting for healthy adults, on exactly this condition. That it works in practice is shown by a study by Germany's Federal Institute for Risk Assessment (BfR) with 36 vegans and 36 people on a mixed diet. Almost all of the vegans supplemented B12, and their B12 status was just as good as that of the mixed eaters, even though they got hardly any B12 from their food.

On the amount, the DGE says quite openly: “There are currently no generally applicable recommendations on the level of supplementation.” Our math above makes the case for a moderate amount every day. BASE delivers more than the estimated daily value, in an amount that's absorbed well every day. And because holo-TC and MMA make your status so easy to measure, an occasional check is the best service you can do yourself as a vegan. Which other nutrients matter on a vegan diet is sorted out in the article on multivitamins for vegans. A real-life example comes from Clara in her story.

Can you take too much vitamin B12?

No harmful amount of vitamin B12 is known so far, which is why there's no official upper limit either. In its overview of upper limits, EFSA lists B12 without a set limit, because no adverse effects have been described. Based on what we know today, the DGE doesn't consider a high intake from food harmful either.

As a precaution, the BfR still proposes a maximum level of 25 µg of vitamin B12 per daily dose of a food supplement. Proposals like these already apply from age 15, factor in a second supplement from the start and aren't law. What can become too much with other vitamins and with several supplements at once is covered in multivitamin side effects and overdose.

What does your body need vitamin B12 for?

Your body needs vitamin B12 above all for blood, nerves and cell division. The DGE describes it, together with folate, as important for making blood, for homocysteine levels and for building genetic material. Homocysteine is an intermediate product of protein metabolism that the body processes further with B12, folate and vitamin B6, so it doesn't build up in the blood.

Officially, eight claims are authorized for vitamin B12, listed in Regulation (EU) No 432/2012: vitamin B12 contributes to normal energy-yielding metabolism, to normal functioning of the nervous system, to normal psychological function, to normal red blood cell formation, to normal homocysteine metabolism, to the normal function of the immune system and to the reduction of tiredness and fatigue, and it has a role in the process of cell division. EFSA assessed them, the EU authorized them. Clunky wording, but what it means is exactly what this whole article has been about: blood, nerves, energy and cells that divide cleanly.

FAQ

When is the best time to take vitamin B12?

At a fixed time you won't forget. With B12, what matters most is the daily supply, and in the study of vegans, those who took their supplement more often had better levels. More on taking it with or without a meal is in how to take a multivitamin.

Are B12 injections better than tablets?

For the everyday supply of healthy people, you don't need an injection, regular amounts you swallow are enough. Whether an injection makes sense is for your doctor to decide, for example when a deficiency has been diagnosed or the stomach can no longer absorb B12 because intrinsic factor is missing. That can only be cleared up in the lab and in conversation.

How long do B12 stores last?

Usually several years. That sounds reassuring, but there's a catch: a shrinking store goes unnoticed for a long time. Holo-TC shows it earlier than any symptom.

Do vegetarians need a B12 supplement?

Not necessarily, but they should keep an eye on their B12 levels. The DGE writes that vegetarians, too, sometimes take in too little B12, and recommends they have their status checked regularly by a doctor. If you hardly eat eggs and dairy, you're already pretty close to the vegan situation.

Is B12 in a multivitamin worth it if I eat meat?

For women in particular, it can be. In Germany's National Nutrition Survey II by the Max Rubner Institute (MRI), measured without supplements, 26% of women didn't even reach the then-lower recommendation of 3.0 µg. Half had a B12 intake at or below today's estimated value of 4.0 µg. If you eat meat, fish and dairy only now and then, a moderate daily amount gives you a reliable foundation, no high dose needed. What else a multivitamin can do is in our multivitamin guide. How B12 works together with the other B vitamins is covered in the article B complex: benefits and how to take it.

Disclaimer:

This article is for informational purposes only and does not replace medical advice, diagnosis, or treatment by a physician or pharmacist. The information provided here should not be used for self-diagnosis or self-treatment. Food supplements are no substitute for a balanced, varied diet and a healthy lifestyle. For any health questions or complaints, please always consult a doctor you trust. Fifty Five accepts no liability for any inconvenience or harm resulting from the use of the information presented here.

Sources

1. Deutsche Gesellschaft für Ernährung (DGE) [German Nutrition Society]: Ausgewählte Fragen und Antworten zu Vitamin B12 (selected questions and answers on vitamin B12). dge.de
2. Herrmann W, Obeid R: Causes and early diagnosis of vitamin B12 deficiency. Deutsches Ärzteblatt International, 2008. pubmed.ncbi.nlm.nih.gov/19623286
3. EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA), Turck D, Bohn T, Castenmiller J et al.: Scientific opinion on the tolerable upper intake level for folate. EFSA Journal, 2023. pmc.ncbi.nlm.nih.gov/articles/PMC10641704
4. Lam JR, Schneider JL, Zhao W, Corley DA: Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA, 2013. pubmed.ncbi.nlm.nih.gov/24327038
5. Aroda VR, Edelstein SL, Goldberg RB et al.: Long-term Metformin Use and Vitamin B12 Deficiency in the Diabetes Prevention Program Outcomes Study. The Journal of Clinical Endocrinology & Metabolism, 2016. pubmed.ncbi.nlm.nih.gov/26900641
6. Deutsche Gesellschaft für Ernährung (DGE) [German Nutrition Society]: Referenzwerte für die Nährstoffzufuhr, Vitamin B12 (reference values for vitamin B12). Derived in 2018. dge.de
7. European Food Safety Authority (EFSA): Summary of Dietary Reference Values, Version 4, September 2017. efsa.europa.eu
8. Regulation (EU) No 1169/2011 of the European Parliament and of the Council of 25 October 2011 on the provision of food information to consumers, Annex XIII. eur-lex.europa.eu
9. Temova Rakuša Ž, Roškar R, Hickey N, Geremia S: Vitamin B12 in Foods, Food Supplements, and Medicines-A Review of Its Role and Properties with a Focus on Its Stability. Molecules, 2022. pubmed.ncbi.nlm.nih.gov/36615431
10. Kurpad AV, Pasanna RM, Hegde SG et al.: Bioavailability and daily requirement of vitamin B12 in adult humans: an observational study of its colonic absorption and daily excretion as measured by [13C]-cyanocobalamin kinetics. The American Journal of Clinical Nutrition, 2023. pubmed.ncbi.nlm.nih.gov/38044024
11. Paul C, Brady DM: Comparative Bioavailability and Utilization of Particular Forms of B12 Supplements With Potential to Mitigate B12-related Genetic Polymorphisms. Integrative Medicine (Encinitas), 2017. pubmed.ncbi.nlm.nih.gov/28223907
12. Zugravu CA, Macri A, Belc N, Bohiltea R: Efficacy of supplementation with methylcobalamin and cyancobalamin in maintaining the level of serum holotranscobalamin in a group of plant-based diet (vegan) adults. Experimental and Therapeutic Medicine, 2021. pubmed.ncbi.nlm.nih.gov/34345275
13. Klug A, Barbaresko J, Alexy U et al.: Neubewertung der DGE-Position zu veganer Ernährung (reassessment of the DGE position on vegan diets). Ernährungs Umschau, 2024. dge.de
14. Weikert C, Trefflich I, Menzel J et al.: Vitamin and Mineral Status in a Vegan Diet. Deutsches Ärzteblatt International, 2020. pubmed.ncbi.nlm.nih.gov/33161940
15. Deutsche Gesellschaft für Ernährung (DGE) [German Nutrition Society]: Ausgewählte Fragen und Antworten zu Nahrungsergänzungsmitteln (selected questions and answers on food supplements). dge.de
16. European Food Safety Authority (EFSA): Overview on Tolerable Upper Intake Levels as derived by the Scientific Committee on Food (SCF) and the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Version 11, August 2025. efsa.europa.eu
17. Bundesinstitut für Risikobewertung (BfR) [German Federal Institute for Risk Assessment]: Höchstmengenempfehlungen des BfR für Vitamine und Mineralstoffe in Nahrungsergänzungsmitteln und angereicherten Lebensmitteln (tabellarische Übersicht) (proposed maximum levels for vitamins and minerals in food supplements and fortified foods, overview table). bfr.bund.de
18. Commission Regulation (EU) No 432/2012 of 16 May 2012 establishing a list of permitted health claims made on foods, other than those referring to the reduction of disease risk and to children's development and health. eur-lex.europa.eu
19. Max Rubner-Institut (Hrsg.): Nationale Verzehrsstudie II, Ergebnisbericht Teil 2 (Germany's National Nutrition Survey II, results report part 2). Karlsruhe, 2008. mri.bund.de