Vitamin B12 Deficiency
Vitamin B12 deficiency causes two separate problems, anaemia and nerve damage, and they do not always show up together. Checking B12 before treating anaemia with folic acid matters more than most people realise.
Medically reviewed by the RIIMS medical team · Last updated: June 2026
Go to hospital now
- Sudden weakness, difficulty walking, or loss of bladder or bowel control (needs urgent neurological assessment)
- Severe breathlessness or chest pain with known significant anaemia
See a doctor soon (not an emergency)
- New or worsening numbness, tingling or unsteady walking
- Anaemia found on a blood test without a clear cause
- Long-term metformin use with no B12 level ever checked
What is vitamin B12 deficiency, and why does it need checking before folic acid?
Vitamin B12 deficiency is common in India, more so in people who eat little or no animal protein, and it causes two separate problems that do not always appear together: anaemia, and damage to nerves. This is where a genuine safety trap lies. High-dose folic acid, often given for anaemia without checking which vitamin is actually low, can correct the blood picture of B12 deficiency, the anaemia looks better, while the nerve damage continues silently underneath, unrecognised because the blood test that prompted concern has normalised. For this reason, B12 should always be checked before folic acid is given for an unexplained anaemia, not assumed. Metformin, one of the most widely used diabetes medicines, is a separate and common cause: long-term use measurably lowers B12 levels, and anyone who has taken it for several years should have a B12 level checked periodically, whether or not they have symptoms. Caught early, B12 deficiency responds well to replacement. The nerve-related symptoms, numbness, tingling, unsteady walking, are the ones to take seriously, because once nerve damage has been present for a long time, it may not fully recover even with treatment, which is exactly why unexplained tingling or numbness deserves a B12 check rather than being dismissed.
Symptoms to watch for
- Tiredness and weakness
- Numbness or tingling in the hands or feet
- Unsteady walking or poor balance
- Pale skin or breathlessness (from anaemia)
- Memory difficulty or low mood
- A sore, smooth tongue
When to consult a doctor
Get a B12 level checked if you have unexplained tiredness, tingling or numbness in the hands or feet, unsteady walking, or have been on metformin for more than a couple of years. Do not accept folic acid alone for an unexplained anaemia without a B12 check first.