Vitamin B12 (Blood Test)
One of the most commonly deficient nutrients in India — especially for vegetarians. Here's what your B12 level actually means and why lab "normal" can be misleading.
Vitamin B12 is critical for your nerves, brain, and red blood cell production. India has an epidemic of B12 deficiency — studies show 47–70% of Indians have suboptimal levels. The lab "normal" range starts too low, so you can be deficient and still see "normal" on your report.
What is the B12 test?
This blood test measures the amount of vitamin B12 (cobalamin) circulating in your blood. B12 is essential for three critical functions: making red blood cells, maintaining the myelin sheath that protects your nerves, and synthesising DNA.
Your body can't make B12 — you get it exclusively from animal foods (meat, fish, eggs, dairy) or supplements. If your intake is low for months to years, your stores gradually deplete. The tricky part: symptoms can be subtle until the deficiency becomes severe — numbness in hands and feet, fatigue, memory issues, and a specific type of anaemia (megaloblastic) where your red cells become abnormally large.
What your number means
| B12 level (pg/mL) | What it means |
|---|---|
| <200 | Deficient — nerve damage risk, needs immediate correction |
| 200–400 | Suboptimal — "grey zone" where many people have symptoms |
| 400–500 | Adequate but not ideal — room for improvement |
| 500–800 | Optimal — where you want to be |
| >800 | Above optimal — fine if supplementing, investigate if not |
Most Indian labs set the lower reference at 200 pg/mL. This means a B12 of 250 shows as "normal" — but at that level, you may already have functional deficiency with elevated homocysteine and methylmalonic acid. If your B12 is under 400, consider supplementation even if the lab says "normal."
How to improve your B12
- Supplement with methylcobalamin — the active form. 1,000–2,000 mcg sublingual daily. Sublingual bypasses gut absorption issues. Available at any pharmacy in India.
- If severely deficient (<200) — your doctor may start with B12 injections (hydroxocobalamin or methylcobalamin IM) for faster repletion, then switch to oral.
- Check folate too — B12 and folate work together. Correcting one without the other can mask problems. Get methylfolate alongside B12.
- Retest at 3 months — B12 stores take time to rebuild. Check again at 90 days after starting supplementation.
- Consider MMA if borderline — Methylmalonic acid (MMA) is the most sensitive marker for true B12 deficiency. If your serum B12 is 200–400 and you have symptoms, an MMA test can confirm functional deficiency.
Don't just test B12 once — track the trend
eterni plots your B12 alongside homocysteine and MCV over time — so you know whether your supplementation protocol is actually working.
Get early accessFrequently Asked Questions
What is a good B12 level for Indians?
Most Indian labs list 200–900 pg/mL as the reference range, but functional deficiency symptoms can appear below 400 pg/mL. Optimal is 500–800 pg/mL. If your B12 is between 200–400, you may feel fine but still have suboptimal nerve and brain function. Below 200 is overt deficiency.
Why is B12 deficiency so common in India?
B12 is found almost exclusively in animal foods — meat, fish, eggs, and dairy. India has one of the highest rates of vegetarianism globally, and even non-vegetarians often eat limited animal protein. Studies show 47–70% of Indians have suboptimal B12 levels. Dairy alone rarely provides enough.
Should I take methylcobalamin or cyanocobalamin?
Methylcobalamin is the active form your body uses directly and is preferred for supplementation. Cyanocobalamin is cheaper and more stable but requires conversion in your body. For most people, 1,000–2,000 mcg of sublingual methylcobalamin daily works well. If you have the MTHFR gene variant, methylcobalamin is particularly important.
Can B12 be too high?
Very high serum B12 (above 1,000 pg/mL) without supplementation can sometimes indicate liver disease, kidney disease, or certain blood cancers — because damaged cells release stored B12 into the blood. If you're supplementing, high B12 is expected and generally safe, as excess is excreted in urine. But if you're not supplementing and your B12 is unusually high, mention it to your doctor.
Why serum B12 isn't the whole story
Serum B12 measures total B12 in your blood, but not all of it is biologically active. About 70–80% is bound to haptocorrin (a transport protein) and isn't available to your cells. Only the fraction bound to transcobalamin — called holotranscobalamin (holoTC) — actually enters your tissues.
This is why someone with a serum B12 of 350 can still have functional deficiency — the active fraction may be low. The most reliable way to confirm: check methylmalonic acid (MMA). MMA rises when your cells don't have enough active B12 to run a key enzymatic pathway. Elevated MMA + borderline serum B12 = treat as deficient.
B12 and homocysteine — the connection
B12 is a required cofactor for converting homocysteine to methionine. When B12 is low, homocysteine accumulates. Elevated homocysteine is an independent risk factor for cardiovascular disease, stroke, and cognitive decline. In many Indians with "normal" B12 levels (250–400), homocysteine is already elevated above 15 µmol/L — a signal that B12 status is insufficient even if it doesn't look low on paper.
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eterni connects your lab results, supplements, and retests — so you can see the trajectory, not just a snapshot.
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