Vitamin B12 Deficiency: The Vegetarian Blind Spot
Vitamin B12 is needed for red blood cell formation, DNA synthesis and the maintenance of the nerve sheath. It occurs naturally almost only in animal foods. That single fact makes deficiency strikingly common in India, where a large proportion of the population eats little or no meat, fish or eggs.
What makes it more serious than most deficiencies is that the neurological damage can become irreversible if it goes uncorrected for long enough.
Symptoms, in two groups
Blood-related:
- Fatigue and weakness
- Breathlessness on exertion
- Pallor, sometimes with a slightly yellow tinge to the skin or eyes
- Palpitations
Neurological, which can appear before anaemia and sometimes without it:
- Tingling, burning or pins and needles in the hands and feet
- Numbness, often starting in the feet and moving up
- Unsteadiness and difficulty walking in the dark
- Memory problems, poor concentration, confusion
- Irritability or depression
- A smooth, sore, red tongue
- Mouth ulcers
The neurological symptoms are the reason a diagnosis matters early. Nerve damage that has been present for many months may not fully recover.
Who is at risk
- Vegetarians and, especially, vegans
- Older adults, in whom stomach acid falls and absorption drops
- People on long-term metformin, which reduces B12 absorption
- People on long-term proton pump inhibitors or H2 blockers
- After stomach or intestinal surgery, including bariatric surgery
- Pernicious anaemia, an autoimmune loss of intrinsic factor
- Coeliac disease, Crohn’s disease and other malabsorption
- Chronic alcohol use
- Breastfed infants of B12-deficient mothers, which can cause serious developmental harm
Testing, and its limitations
Serum B12 is the usual first test, but it is imperfect. Levels in the low-normal range may still represent deficiency at tissue level, and the test can read falsely normal in some conditions.
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Where the clinical picture suggests deficiency but serum B12 is borderline, methylmalonic acid and homocysteine are more sensitive; both rise in true deficiency.
A complete blood count may show large red cells (high MCV), but a coexisting iron deficiency — very common in India — can mask this and keep the MCV normal. A normal MCV does not rule out B12 deficiency.
Two further points worth knowing:
- Folate supplementation can correct the anaemia of B12 deficiency while the neurological damage continues silently. B12 must be checked and corrected before or alongside folate.
- Start testing before starting supplements; taking B12 for a few weeks makes the result uninterpretable.
Correcting it
Where absorption is normal — that is, dietary deficiency in a vegetarian — high-dose oral B12 works well. Typical regimens use 1000-1500 mcg daily. A small fraction is absorbed passively without intrinsic factor, which is enough at these doses.
Where there is malabsorption — pernicious anaemia, after gastric surgery, severe deficiency with neurological signs — intramuscular injections are used initially, often on alternate days for one to two weeks, then monthly or three-monthly maintenance. High-dose oral therapy can maintain many of these patients afterwards, but the loading is usually given by injection.
Improvement in blood counts begins within a week or two. Neurological recovery is slower, taking months, and may be incomplete.
Because the underlying cause usually persists — a vegetarian diet, metformin, age-related absorption — treatment is generally long term rather than a single course.
Dietary sources
For vegetarians: dairy is the main natural source, so milk, curd and paneer matter. Eggs, for those who eat them, contribute. Fortified foods — some breakfast cereals, fortified milk and plant milks, nutritional yeast — help. Plant foods, including fermented products, spirulina and seaweed, are not reliable sources; some contain analogues that do not work in humans and may even interfere.
For most lifelong vegetarians in India, diet alone does not reliably cover requirements, and a supplement is the practical answer.
When to see a doctor
- Persistent tingling or numbness in hands or feet
- Unsteadiness or falls
- Memory or concentration problems with fatigue
- Anaemia that has not been explained
- If you are vegetarian, pregnant or planning pregnancy, since deficiency affects the baby
- Long-term metformin or acid-suppressing medication without a B12 check
This article is general health information. B12 deficiency should be confirmed and treated under medical supervision, particularly where neurological symptoms are present.