Vitamin B12

What it is

Vitamin B12 (cobalamin) is found almost only in animal foods: meat, fish, eggs and dairy, plus fortified foods like some plant milks, yeast extract and cereals. It is stored in the liver, so deficiency can take years to appear.

People take it for tiredness, mood, nerves and as a vegan safeguard. It is genuinely needed by anyone who avoids animal products and by many older adults and people on certain medicines who absorb it poorly.

This page is about tablets, sprays and sublingual forms. Injections (for pernicious anaemia, for example) are prescribed and are a separate subject; the peptide-adjacent B12 page covers injectable use.

How it works

B12 is needed to make red blood cells, maintain nerve insulation and process homocysteine and certain fats. Absorption from food needs stomach acid and a protein called intrinsic factor; at high oral doses, a small percentage is absorbed passively without it.

What the evidence says

• Strong Correcting B12 deficiency and related anaemia
  Effective, including high-dose oral B12 for many people, though some need injections.
• Strong Preventing deficiency in vegans and vegetarians
  Supplements or fortified foods are recommended for vegans.
• Moderate Nerve health in deficiency (tingling, numbness)
  Improves when deficiency is the cause; early treatment matters.
• Weak More energy in people who are not deficient
  There is no good evidence that extra B12 boosts energy if your levels are normal.
• Limited Mood and memory
  Low B12 is associated with both, but supplementing replete people has not shown clear benefit.

Evidence ratings are our plain-English summary of how much good human research exists, not a promise of results. How we rate evidence.

Dosage and timing

• UK adult reference intake is 1.5 micrograms a day; the NHS says taking 2 mg or less a day is unlikely to cause harm.
• Vegans commonly take 10 micrograms daily or 2,000 micrograms weekly; check current guidance.
• Sublingual versus swallowed makes little difference to absorption in most studies.
• If you have symptoms of deficiency, get a blood test rather than self-treating, as a supplement can mask the cause.

Forms and what to look for

• Cyanocobalamin is the most studied, stable and cheap form; the tiny cyanide part is harmless at these doses.
• Methylcobalamin is a natural form often marketed as superior; evidence that it works better is limited.
• Hydroxocobalamin is what the NHS uses for injections.
• Adenosylcobalamin appears in some blends; again, no proven advantage.
• Fortified foods and yeast extracts can also provide B12.

What to expect, and when

• If deficient, energy and blood counts can improve over weeks.
• Nerve symptoms may take months to improve, and sometimes do not fully recover.
• If you are not deficient, expect no noticeable change.

Side effects

• Generally very well tolerated.
• Rarely, acne-like breakouts or rosacea flare with very high doses.
• Mild headache, nausea or diarrhoea.
• Allergic reactions are rare.

Interactions

• Metformin can reduce B12 absorption over years.
• Proton pump inhibitors and H2 blockers (such as omeprazole, ranitidine alternatives) lower stomach acid and reduce absorption.
• Colchicine and some antibiotics can reduce absorption.
• Very high doses can affect some lab tests.
• Taking folic acid alone can hide B12 deficiency anaemia.

Who should avoid it

• Anyone with unexplained tingling, numbness, balance problems or memory changes should see a doctor rather than just supplement.
• People with Leber hereditary optic neuropathy should avoid cyanocobalamin.
• People with kidney disease should check which form to use.
• Anyone with a known allergy to cobalt or cobalamin.

Risks and safety

• Very low toxicity, but taking supplements before testing can mask pernicious anaemia and delay diagnosis.
• Not banned in sport.
• Large doses can raise measured levels without helping if there is a functional block.
• Sprays and sublingual products often have wildly high micrograms labelled; they are not better, only pricier.

Buying well: quality and testing

• Check the micrograms per serving.
• Plain cyanocobalamin from a reputable brand is fine.
• Third-party seals (NSF, USP, Informed Sport) add reassurance.
• Avoid "energy" blends where B12 is surrounded by caffeine and stimulants and you cannot tell what is doing what.

Bottom line

For vegans, older adults and people on long-term metformin or acid-reducing medicines, B12 is one of the most justified supplements. For everyone else, a high dose is unlikely to give you more energy; if you feel constantly tired, ask your GP for a blood test.