Vitamin B12 Vitamin B12 (Cobalamin)
A vitamin from animal foods that your nerves and red cells need.
Also printed asB12 · Cobalamin · Cyanocobalamin · Methylcobalamin
What it measures
A vitamin found almost only in animal foods, needed to build red cells and maintain nerve insulation.
A shortfall enlarges red cells, raises homocysteine, and causes tingling, poor balance and low mood before anaemia ever shows.
Why it matters for how long you stay well
Nerve damage from a long shortage can become permanent, and vegetarian diets are the norm across much of India, which makes this one of the most worthwhile numbers on the panel to check and correct.
How it shows up in daily life
Running low can bring tingling in your hands and feet, forgetfulness, a sore tongue and a tiredness that iron does not fix.
High and low readings
When it reads high
Usually from supplements or injections, and harmless.
When it reads low
Common on a vegetarian diet; nerve symptoms can appear before the blood count changes.
What moves it
Daily life
- eggs, dairy, fish and meat
- a vegetarian or vegan diet
- how well your stomach absorbs it, which falls with age
- alcohol
Medicines known to shift it
- vitamin B12 supplements (raise it)
- metformin (lowers it)
- PPIs (lower it)
Listed so a result can be read in context. It is not advice to start, stop or change any medicine; that decision belongs with your physician.
Read it with
Markers that move this one, or that this one moves. One number read alone can mislead.
- Red cell sizeKnown mechanism
As this rises, Red cell size falls as it rises
Without enough B12 your body builds oversized red cells. So a low B12 shows up on the blood count as a raised cell size.
- HomocysteineKnown mechanism
As this rises, Homocysteine falls as it rises
B12 is one of the tools your body clears homocysteine with. When B12 runs short, homocysteine has nowhere to go and backs up.
- Red cell size spreadObserved association
As this rises, Red cell size spread falls as it rises
New oversized cells mixing with normal ones widens the spread of red cell sizes. So a widening spread can be the first hint of a B12 shortage.
Common questions
What does Vitamin B12 (Cobalamin) measure?
A vitamin found almost only in animal foods, needed to build red cells and maintain nerve insulation. A shortfall enlarges red cells, raises homocysteine, and causes tingling, poor balance and low mood before anaemia ever shows.
What does a high Vitamin B12 result usually mean?
Usually from supplements or injections, and harmless.
What does a low Vitamin B12 result usually mean?
Common on a vegetarian diet; nerve symptoms can appear before the blood count changes.
What is the usual reference range for Vitamin B12?
A broad adult reference band is 300–900 pg/mL. Labs differ, so read your result against the band printed on your own report.
Educational only, not a diagnosis. A single number means little without your history and the rest of your panel, so discuss your own results with your physician.
Typical adult reference band
- Adults
- 300–900 pg/mL
Labs differ. The band printed on your own report is the one that applies to your result.
Reported in pg/mL, pmol/L
Ageing relevance
3/5
A moderate ageing association; used in clinical longevity panels.
Indian reference data
Published data on this marker in Indian adults: Yajnik et al. 2006, 441 men in Pune (PMID 17214273): median 110 pmol/L, 67% below 150 pmol/L.
Worth knowing
Your liver stores enough to last years, which is why a shortage takes a very long time to show itself.
Have a report with this marker on it? Read it in context.
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