Vitamin B12Cobalamin
A vitamin essential for healthy nerves and red blood cells.
Vitamin B12, or cobalamin, is essential for making red blood cells, for DNA synthesis and for maintaining the myelin sheath around nerves. It comes almost entirely from animal foods, because the bacteria that produce it are not part of plant tissue.
Deficiency is one of the more consequential nutritional shortfalls, because the nerve damage it causes can become permanent. The typical picture is fatigue and anaemia first, then pins and needles, unsteadiness, memory and mood changes if it continues.
Absorption is unusually complicated, which is why deficiency is not only about diet. B12 needs stomach acid to be released from food and intrinsic factor from the stomach lining to be absorbed in the ileum, so pernicious anaemia, gastric surgery, coeliac and Crohn's disease, long term acid suppressing medication and metformin can all cause deficiency in someone eating plenty.
Some groups should supplement as a matter of routine rather than waiting for symptoms: vegans and most vegetarians, older adults, and anyone with the absorption problems above. For everyone else already replete, extra B12 does nothing, and the energy claims on B12 drinks and shots apply only to correcting a deficiency.
One interaction is worth knowing. High dose folic acid can correct the anaemia of B12 deficiency while the nerve damage progresses underneath, which is why the two are checked together and why treating a macrocytic anaemia without establishing the cause is a mistake.
It is water soluble and remarkably safe in excess, with the liver holding a reserve that can last years, which is also why deficiency in a new vegan may take a long time to appear and then arrive without warning.
In practice: if you avoid animal foods, supplement routinely; if you have unexplained fatigue, tingling or anaemia, ask for B12 and folate to be checked together rather than guessing.
Where your own result would sit
Most people reading this page are holding a blood-test report with this marker on it, and the question they arrived with is whether their number is normal. A reference interval says where most results from a healthy population fall; a guideline threshold is where a clinical body draws a line for a decision. Neither is a target, and a result on the wrong side of one is not a diagnosis: the same number can be unremarkable in one person and worth looking into in another, which is why the clinician who ordered the test reads it against your history rather than against a list.
Vitamin B12 has no published interval on this page yet. We hold one, and the dashboard draws it beside a reader’s own result, but it has not been read back against the laboratory’s own page since it was collected. A figure printed beside somebody’s blood result has to have been seen at its source, not remembered, so this one waits.
On your own blood test?
Vitamin B12 is one of the markers FitTools can read from an uploaded blood-test report. You confirm every value before anything is saved, and your results are explained together in one place.