Vitamin B12 levels: what your result means
Last updated: 24 September 2026
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Vitamin B12, or cobalamin, is needed to make red blood cells, to keep the nervous system working, and for DNA synthesis. The body cannot make it, so it comes entirely from animal foods or supplements, and it is stored in the liver in quantities that last years — which is why a deficiency usually develops slowly and quietly.
The standard test measures total B12 in serum. It is a reasonable screen, but a blunt one: most of what it counts is bound to a protein the body cannot readily use, so the number can look acceptable while the usable fraction is low.
Typical B12 ranges
| Result | pg/mL | pmol/L |
|---|---|---|
| Deficient | below 200 | below 148 |
| Borderline | 200–300 | 148–221 |
| Normal | 300–900 | 221–664 |
| Above range | above 900 | above 664 |
What lowers B12
- A diet without animal products. Vegans, and to a lesser extent vegetarians, have no dietary source unless they supplement or eat fortified foods.
- Pernicious anaemia, an autoimmune condition that destroys the intrinsic factor B12 needs in order to be absorbed. It is a common cause in older adults and is diagnosed with antibody testing.
- Metformin, which reduces absorption over years of use. Long-term users are often monitored for it.
- Acid-reducing medication, including proton pump inhibitors and H2 blockers, since stomach acid is needed to release B12 from food.
- Age. Atrophic gastritis becomes more common with age and reduces absorption even on a normal diet.
- Gut surgery or disease affecting the stomach or the end of the small intestine, including Crohn’s disease and bariatric surgery.
Why a low B12 is worth catching early
Untreated deficiency causes anaemia, but the part that matters most is neurological: numbness and tingling in the hands and feet, balance problems, and memory or mood changes. Nerve damage from prolonged deficiency can become permanent, which is why it is treated rather than watched.
One subtlety worth knowing: high folate intake can correct the anaemia while leaving the nerve damage progressing, so a normal full blood count does not rule out B12 deficiency.
What a high B12 usually means
Almost always supplementation, including B12 in a multivitamin or an energy drink. There is no established toxicity from high B12 in healthy people, and the body excretes the excess.
A high result in someone who is not supplementing is a different matter and is worth investigating, since it can accompany liver disease or some blood disorders.
Testing while supplementing
A serum B12 drawn while you are taking a supplement mostly tells you that you took a supplement. If the question is whether you truly need one, the level has to be measured before starting, or well after stopping — which is a decision to make with your doctor rather than alone.
This is exactly the case where your own history is worth more than a single number, because what matters is where your level sits when nothing is propping it up.
Common questions
What is a normal vitamin B12 level?
Most labs treat roughly 200–900 pg/mL (148–664 pmol/L) as normal, though the lower cut-off is debated and some clinicians consider anything under 300 pg/mL worth a second look, particularly with symptoms.
Can B12 be low even if I eat meat?
Yes. Absorption problems cause more deficiency than diet does — pernicious anaemia, long-term metformin or acid-reducing medication, and age-related changes in the stomach all reduce how much B12 you take up regardless of what you eat.
Does metformin lower B12?
It can, gradually, over years of use. Guidelines suggest periodic B12 testing for long-term metformin users, especially anyone with symptoms of neuropathy.
Keep your results in one place
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