Nutrients & electrolytes
Also known as Cobalamin. Measured in pg/mL.
Vitamin B12 is required for red blood cell formation, DNA synthesis and the maintenance of the myelin sheath around nerves. It occurs naturally almost exclusively in animal foods, which makes deficiency common in vegetarian and vegan diets unless supplemented or obtained from fortified products. Deficiency develops slowly, because the liver stores several years' worth, and it presents in two overlapping ways: a blood picture of enlarged red cells and anaemia, and a neurological picture of numbness, tingling, unsteadiness, poor concentration and low mood. The neurological damage can become permanent if deficiency persists, which is the main reason it is worth detecting early. The standard serum B12 test has a well-known weakness — it measures total B12, most of which is bound to a protein that cells cannot use.
Roughly 80% of serum B12 is bound to haptocorrin and unavailable to cells, so a normal total B12 can accompany real deficiency.
Active B12 (holotranscobalamin) and homocysteine detect cases that total B12 misses.
Neurological damage from prolonged deficiency may not fully reverse, which is the argument for early detection.
High serum B12 usually reflects supplementation and is not itself harmful, since excess is excreted. Unexpectedly high B12 in someone not supplementing occasionally accompanies liver disease or certain blood disorders and is worth mentioning to a physician rather than ignoring.
Low B12 causes fatigue, brain fog, low mood, and — as it progresses — tingling or numbness in the hands and feet, unsteadiness and memory difficulty. Anaemia with enlarged red cells is the classical finding but frequently appears late or not at all, so neurological symptoms can precede any blood-count abnormality.
| Band | Value |
|---|---|
| Deficient | < 200 pg/mL |
| Borderline | 200 – 300 pg/mLSymptoms are common in this band; check active B12 and homocysteine |
| Adequate | > 300 pg/mL |
Laboratory intervals vary. Interpret with a physician.
B12 deficiency is one of the most common and most consistently overlooked nutritional gaps in India, and follows directly from the proportion of the population eating little or no animal protein. It is frequently misattributed to overwork or stress because the early symptoms — tiredness, poor concentration, low mood — are exactly what a demanding job is assumed to cause.
Homocysteine is an amino acid produced continuously as the body processes methionine from dietary protein.
Ferritin is the protein the body uses to store iron, and the amount circulating in blood is proportional to how much iron is held in reserve.
HbA1c measures the proportion of haemoglobin in your red blood cells that has sugar attached to it.
Numbness, tingling, unsteadiness or memory change should be assessed promptly, as neurological damage from prolonged deficiency can become irreversible. A borderline B12 with symptoms deserves a physician's view rather than watchful waiting, since the standard test understates true deficiency in a meaningful proportion of people.
Yes, and it is common. Serum B12 measures total circulating B12, but roughly 80% of it is bound to haptocorrin and unavailable to cells. Active B12 (holotranscobalamin) measures the usable fraction, and homocysteine rises functionally when cells are short. Either can be abnormal while total B12 reads normal.
Most do. Plant foods contain essentially no reliable B12, and fermented foods and algae are not dependable sources. Dairy contributes some, which is why lacto-vegetarian diets fare better than vegan ones, but often not enough to maintain adequate levels long-term.
Blood markers respond within weeks. Neurological symptoms improve much more slowly and may not resolve completely if deficiency has been prolonged, which is the argument for detecting it early rather than waiting for symptoms to declare themselves.
The programme
Peak Brain draws a full blood and urine panel at your home, has a licensed physician read every marker together rather than one at a time, and turns what they find into a ranked 90-day protocol with a retest at the end.
Authorship & review
Written by the Peak Brain clinical team. Assigned clinical reviewer: Dr. Arjun, MD, DM — review pending; this page has not yet been signed off.
Published . Last updated .
This page is general health information, not medical advice, diagnosis or treatment. Reference ranges vary between laboratories. Never delay or disregard advice from a qualified health professional because of something you read here. If you think you may have a medical emergency, call your local emergency number.