Wellness . Symptoms guide
Vitamin B12 Deficiency: Symptoms and Testing
B12 deficiency can cause fatigue, hair shedding, brain fog, low mood, tingling or numbness, and in severe cases neurological damage. It is particularly common in vegans, vegetarians, older patients and after gastric surgery. Testing before supplementing matters because supplements can mask the deficiency in routine blood tests.
This patient information is being clinically reviewed by our team. The factual content draws on UK guidance (NHS, NICE, British Association of Dermatologists, British Society for Sexual Medicine where cited).
What this might be
- Vegan or vegetarian diet. B12 is almost exclusively in animal products.
- Pernicious anaemia. Autoimmune loss of stomach factor needed for absorption.
- Metformin and PPI use. Both reduce B12 absorption over time.
- Coeliac disease and Crohn disease. Reduced absorption.
When to seek urgent advice
If any of the following apply, please contact your GP, NHS 111, or A&E in the first instance rather than waiting for private bloodwork.
- Numbness or tingling in hands or feet
- Difficulty walking or unsteadiness
- Memory problems
Common features that suggest this
- Persistent fatigue
- Hair shedding
- Pale skin or yellow tinge
- Sore, red tongue
- Tingling in hands or feet
- Memory or concentration problems
Recommended tests
Same-day appointments at our Harley Street clinic, results clinician-reviewed.
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Testing advice
No fasting. Stop B12 supplements at least 1 month before testing for an accurate baseline if your prescriber agrees.
Common questions
What should B12 levels be?
UK reference ranges vary, typically 200 to 900 ng/L. Levels under 200 are deficient; symptomatic patients may benefit from levels above 400.
Do I need injections or are tablets enough?
Depends on cause. Dietary deficiency responds to high-dose oral B12. Pernicious anaemia and post-gastric-surgery deficiency may need injections. Bloodwork is the start of the decision.
Related symptoms
Sources and further reading
This page provides general information only and is not a substitute for medical advice. A GMC-registered clinician will review your results and tailor any recommendations to you personally.