B12 is good for seven things officially approved by the European Food Safety Authority EFSA: energy-yielding metabolism, normal functioning of the nervous system, normal homocysteine metabolism, normal psychological function, normal red blood cell formation, normal immune system function, and the reduction of tiredness and fatigue. All official EFSA claims from Regulation 432/2012 — not marketing promises.
What that means in practice: when you get enough B12 your body barely registers it. When you are deficient, you feel it on several levels at once: fatigue, concentration problems, sometimes tingling in your fingers or feet. Below is an honest guide: what B12 does, how much you need, where to get it, who is at risk, and when supplementation is actually warranted.
What vitamin B12 does in your body
B12 (official name: cobalamin) is a water-soluble vitamin involved in several interconnected processes.
Energy-yielding metabolism. B12 helps the enzymes that convert carbohydrates and fats into usable energy. A deficiency therefore first shows up as unusual fatigue that does not resolve with rest.
Nervous system. B12 is needed to produce myelin — the protective sheath around nerves that allows fast signal transmission. A prolonged deficiency may cause tingling or numbness in hands and feet, and in rare severe cases coordination problems.
Red blood cell formation. B12 works together with folic acid to produce new red blood cells. A deficiency creates large, slowly maturing cells — known as megaloblastic anaemia and visible on a simple blood test.
Psychological function and mood. B12 is involved in the production of neurotransmitters (serotonin, dopamine). In older adults a long-running B12 deficiency is sometimes mistaken for dementia or depression — often reversible if caught in time.
Homocysteine metabolism. B12 helps convert the amino acid homocysteine. Elevated homocysteine in your blood is associated with a higher risk of cardiovascular disease — although the causal relationship is still being researched.
How much vitamin B12 you need per day
The Dutch Health Council recommends 2.8 micrograms (µg) per day for adults as the recommended daily allowance (RDA). That is fairly low compared with other vitamins — one egg (~1.1 µg) and a glass of milk (~0.5 µg) already get you most of the way.
It varies slightly by age group: children 1-3 years 0.7 µg · children 9-13 years 2.0 µg · adults 18+ 2.8 µg · pregnant 3.3 µg · breastfeeding 3.8 µg.
Upper limit? Practically there is none. B12 is water-soluble — anything in excess you simply excrete. A toxic intake from food in normal use is not possible; even supplementation at 1,000 µg produces no toxicity according to the European Food Safety Authority.
Foods rich in vitamin B12
B12 only occurs in animal products. Plant sources (seaweed, fermented foods, brewer's yeast) contain forms your body either cannot or hardly uses — you cannot rely on them.
Top sources per 100 grams (relative to the 2.8 µg RDA): liver 90 µg (32× RDA) · mussels 19.6 µg (7× RDA) · sardines 12 µg (4.3× RDA) · salmon 3 µg (107%) · beef 2 µg (71%) · matured cheese 2.4 µg (86%) · egg 1.1 µg each (39%) · semi-skimmed milk 0.5 µg per glass (18%).
In practical terms: one portion of fish per week plus daily dairy or an egg brings most people well above the RDA. The Dutch who fall short according to the Voedselconsumptiepeiling are mainly vegans and some older adults.
Who is at risk of a vitamin B12 deficiency
B12 deficiencies are rare in the Netherlands among healthy adults with a normal diet. In a few specific groups the risk is higher.
Vegans and strict vegetarians. Without animal products you simply cannot get it from food. A daily supplement or fortified products (some plant-based milks, vegan meat substitutes) are not a luxury but standard.
Older adults from 60-65. With age your stomach produces less stomach acid and less intrinsic factor — both needed to absorb B12. A deficiency creeps in slowly, often masked by 'ah, I am getting older'.
People taking metformin (diabetes type 2). Metformin measurably inhibits B12 absorption in the gut. The GP should mention this at the prescription, though that does not always happen in practice.
Stomach or gut disorders. Pernicious anaemia, coeliac disease, Crohn's, Roux-en-Y gastric bypass, long-term PPI use (acid blockers) — all can disturb absorption. Here a blood test is the instrument, not assumption.
Pregnant women and young children of mothers with low B12. B12 is needed for the formation of the child's nervous system. When in doubt: GP or midwife.
Symptoms of a B12 deficiency — what to watch for
B12 deficiencies are insidious. The complaints are so generic that they are often attributed to other causes.
Early signals: persistent fatigue that does not resolve with rest, concentration problems, shortness of breath sooner than normal, paleness, quickly irritated.
Later signals: tingling or a numb feeling in hands or feet (neuropathy), balance problems, forgetfulness, sometimes a smooth red tongue or mouth ulcers.
Severe signals: confusion, behavioural changes, coordination problems. These are reasons to see a GP quickly, because recovery takes longer the longer the deficiency is untreated.
One dry observation: fatigue has ten possible causes. B12 deficiency is one of them. Checking it via a blood test before reaching for a supplement is sensible — not the other way round.
When (and how) supplementation makes sense
The order of decision: blood test first, supplement second. The GP tests your serum B12 (reference: under 150 pmol/L is deficiency, 150-250 pmol/L is the grey zone, above 250 pmol/L is normal). Sometimes MMA is also measured (methylmalonic acid — a more sensitive marker for borderline cases).
At proven deficiency. Tablets of 1,000 µg per day work for most people because about 1 percent is absorbed passively — even without intrinsic factor. For severe deficiency or pernicious anaemia the GP prescribes injections (hydroxocobalamin), usually 5-10× over two weeks, then a maintenance dose per month or quarter.
At elevated risk without deficiency. Vegans and strict vegetarians: daily 5-25 µg via a supplement or fortified products. Older adults uncertain about their diet: 25-100 µg per day is a reasonable maintenance dose. Above that has no extra effect.
Methylcobalamin versus cyanocobalamin. Methyl is the active form, cyano the more stable synthetic version your body converts to methyl itself. In practice both work equally well for most people. Heavy smokers or those with kidney issues sometimes prefer methylcobalamin.
What vitamin B12 does NOT do
Marketing for B12 supplements often suggests more than the science supports. A few myths worth dispelling.
B12 does not wake you up if you have no deficiency. With normal B12 status extra B12 does nothing to your energy level. Energy drinks with 'B12 for extra energy' work mainly because of caffeine, not the B12.
B12 is not a beauty vitamin. That 'B12 is good for skin, hair and nails' is a persistent claim EFSA has not approved. The Voedingscentrum confirms: there is no direct link.
B12 does not replace treatment. For severe fatigue, depression or neuropathy B12 is one possible cause — but rarely the whole answer. Having a GP rule out other causes (thyroid, iron, sleep, mental health) is always sensible.
When you are better off seeing your GP
Self-supplementing on suspected symptoms is tempting but not always wise.
Persistent fatigue lasting longer than six weeks. Find the cause first — B12 is one of ten possibilities. A blood test at the GP takes fifteen minutes.
Tingling, numbness or balance problems. These are neurological signals where B12 may play a role, but other conditions too. No self-diagnosis.
When taking metformin, PPIs or after stomach/gut surgery. Actively ask for a B12 measurement in your annual blood test. It is not standard in a GP package.
Vegans who do not yet supplement. Start with a low-threshold supplement (5-10 µg per day) and have B12 measured once every two years. Safer than discovering a deficiency once every five years.
Frequently asked questions
What is the difference between B12 and vitamin B complex?
Vitamin B complex is a collective name for eight different B vitamins (B1, B2, B3, B5, B6, B7, B9 and B12). Each has its own function. B12 is one of them — the only one that occurs only in animal products and that your liver stores for months. A B-complex supplement contains all eight; a stand-alone B12 supplement is usually enough for those deficient only in that one.
Can you get too much vitamin B12?
Not in practical terms. B12 is water-soluble — anything in excess you simply excrete. Even high doses of 1,000-5,000 µg per day produce no toxic effects according to EFSA. An extremely high B12 level in blood can however sometimes indicate another underlying condition (liver problems, certain blood disorders) — a GP looks at this separately.
Does B12 really help against fatigue?
Only if you have a deficiency. The EFSA claim is verbatim: 'Vitamin B12 contributes to the reduction of tiredness and fatigue' — which means it does its job at adequate B12 status. If your B12 is normal and you feel tired, extra B12 tablets do nothing. Fatigue can also come from sleep, stress, thyroid function, iron or vitamin D deficiency.
How much B12 is in one egg?
About 1.1 micrograms per egg (medium size, ~50 g). That covers 39 percent of the recommended daily allowance for an adult. Two eggs plus a glass of milk and some cheese on bread: you are well above the norm. For people with a mixed diet a daily B12 supplement is rarely needed.
What is the difference between methylcobalamin and cyanocobalamin?
Methylcobalamin is the active form as your body uses B12; cyanocobalamin is the synthetic, more stable form in supplements that your body converts to methyl itself. For most people both work equally well. Cyano is generally cheaper and has a longer shelf life. Methyl is sometimes recommended for those with kidney problems or heavy smokers, because the body then has more trouble excreting the cyanide residue.
How long does it take for B12 supplementation to work?
With a mild deficiency you often notice improvement in fatigue and concentration within two to four weeks. With neurological complaints (tingling) recovery takes longer — three to six months is normal, and in severe cases recovery may be incomplete. With severe deficiency or pernicious anaemia the GP treats with injections, which work faster than tablets.