Low vitamin b12

Written to our editorial standards · reviewed against published research· Updated 2 Jun 2026

Low B12 causes fatigue, brain fog, and tingling, and matters because the nerve damage it causes can become permanent if it is missed, so it is worth correcting promptly.

B12 is needed to make red blood cells and to maintain the protective sheath around nerves, so a deficiency causes both anaemia-type fatigue and neurological symptoms like pins and needles. Risk is higher in vegans, older adults, and people on metformin or acid-blockers. Folate can mask the blood signs while nerve damage continues.

Common causes

  • Vegan or low-animal-product diet
  • Older age (reduced absorption)
  • Metformin or long-term acid-blockers
  • Pernicious anaemia (autoimmune)
  • Gut conditions affecting absorption

Associated symptoms

  • Tingling or numbness in hands or feet
  • Brain fog and poor memory
  • Fatigue
  • Low mood
  • A sore, red tongue

Nutrients that can help

Methyl-B12
See the guide →
Methylfolate
See the guide →
What to do

Take B12, choosing a sublingual or higher-dose form if absorption is the issue. If you are vegan, older, or on metformin, this is a maintenance supplement, not a one-off. Recheck after a few months.

When to see a doctor

New or worsening numbness, or a very low B12, needs a doctor to find the cause (pernicious anaemia needs injections) and to protect the nerves before damage sets.

Full marker
Vitamin B12: ranges, what it measures & both directions
Read the Vitamin B12 guide →

Common questions

What does low vitamin b12 mean?
Low B12 causes fatigue, brain fog, and tingling, and matters because the nerve damage it causes can become permanent if it is missed, so it is worth correcting promptly. B12 is needed to make red blood cells and to maintain the protective sheath around nerves, so a deficiency causes both anaemia-type fatigue and neurological symptoms like pins and needles. Risk is higher in vegans, older adults, and people on metformin or acid-blockers. Folate can mask the blood signs while nerve damage continues.
What causes low vitamin b12?
Vegan or low-animal-product diet; Older age (reduced absorption); Metformin or long-term acid-blockers; Pernicious anaemia (autoimmune); Gut conditions affecting absorption.
How do I raise my vitamin b12?
Take B12, choosing a sublingual or higher-dose form if absorption is the issue. If you are vegan, older, or on metformin, this is a maintenance supplement, not a one-off. Recheck after a few months.
When should I see a doctor?
New or worsening numbness, or a very low B12, needs a doctor to find the cause (pernicious anaemia needs injections) and to protect the nerves before damage sets.

Have your full results?

Upload your bloodwork and we'll read every marker, flag what's off, and match evidence-led, targeted support.

Analyse my bloodwork →

Educational use only, not medical advice or diagnosis. Reference ranges vary by lab, age, sex, and medication, and a single result is read in context. Always review your results with a qualified clinician.