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Strong evidenceGeneral health

Vitamin B12

Essential for red blood cells and the nervous system. Supplementation is clearly effective — and often necessary — for vegans, older adults, and people with absorption problems.

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What the science says

  • Correcting and preventing deficiency Strong evidence

    B12 deficiency causes anemia and neurological damage that can become irreversible if untreated. Oral supplementation reliably corrects deficiency, including at high oral doses as an alternative to injections in most people.

  • Essential for vegans and many older adults Strong evidence

    B12 occurs naturally only in animal foods, so supplementation is the standard recommendation for vegans. Up to 20% of older adults absorb food-bound B12 poorly (atrophic gastritis) and benefit from supplements or fortified foods.

  • Energy boost in people with normal levels Limited evidence

    Despite the marketing, there is no good evidence that extra B12 improves energy or cognition in people who are not deficient.

Dosage & safety

Studied doseAdults need only 2.4 mcg/day, but because absorption of large doses is inefficient, supplements commonly provide 250–1,000 mcg/day (cyanocobalamin or methylcobalamin — both work).
SafetyVery safe; excess is excreted. No established upper limit. Deficiency should be confirmed and monitored with blood tests.

How to take it

TimingTiming does not matter.
With food?With or without food — the large doses in supplements are absorbed passively and do not depend on stomach acid.
Worth knowingSublingual and spray forms are not better than a swallowed tablet; the evidence shows equivalent results, so buy on price.

Interactions

With medications

  • metformin

    Long-term metformin reduces B12 absorption and is a common cause of unrecognised deficiency. have B12 checked periodically if you have taken metformin for years

  • proton pump inhibitors and H2 blockers

    Stomach acid is needed to release B12 from food, so long-term acid suppression lowers B12 status. check levels after prolonged use; supplemental B12 does not need acid and works fine

  • nitrous oxide (recreational or repeated anaesthetic use)

    Nitrous oxide inactivates B12 and can precipitate severe neurological damage in someone already low. correct a deficiency before elective exposure and seek urgent review if numbness or gait problems appear

With other supplements

  • high-dose folic acid

    Folate corrects the anaemia of B12 deficiency while nerve damage keeps progressing unnoticed. check B12 before taking more than 400 mcg/day of folate long-term

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Do vegans need to take vitamin B12?

Yes — the evidence is strong. Vitamin B12 occurs naturally only in animal foods, so B12 supplementation is the standard recommendation for vegans; up to 20% of older adults also absorb food-bound B12 poorly.

How much vitamin B12 per day?

Adults need only 2.4 mcg/day of vitamin B12, but because large doses are absorbed inefficiently, B12 supplements commonly provide 250–1,000 mcg/day. Cyanocobalamin and methylcobalamin both work.

Does vitamin B12 give you more energy?

Not if your levels are normal — the evidence is limited. Despite the marketing, there is no good evidence that extra vitamin B12 improves energy or cognition in people who are not deficient.

Can metformin cause vitamin B12 deficiency?

Yes. Long-term metformin reduces vitamin B12 absorption and is a common cause of unrecognised deficiency, so have your B12 checked periodically if you have taken metformin for years.

Scientific references

Where to buy

Life Extension, Vitamin B12, Methylcobalamin, 500 mcg, 100 Vegetarian Lozenges

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