Vitamin B12

Vitamin B12 (cobalamin) is essential for nerve function, red-cell production, and DNA synthesis. It is absorbed via a process requiring stomach acid and intrinsic factor, which is why absorption — not just intake — commonly fails.

B12 deficiency is one of the genuinely reversible causes of cognitive impairment, neuropathy, and anaemia — which is exactly why it is checked in any cognitive workup. Correcting a real deficiency matters enormously; supplementing beyond repletion does not improve cognition.

1. 1

   FoundationBrain & Cognitive HealthThe best place to understand what actually protects the brain — and why most nootropics don't.
2. 2

   ConditionMild Cognitive ImpairmentCognitive decline beyond normal ageing — but not dementia
3. 3

   Signal RecordMetforminBiguanide (first-line for type 2 diabetes)
4. 4

   Body SystemBrainCognition, mood, memory, and neurological health.
5. 5

   BiomarkerHomocysteineA vascular and cognitive risk marker — with a caveat

1. Measure it
2. Understand your result
3. See what raises and lowers it
4. Apply evidence-based interventions
5. Recheck on your review cadence

An orientation to how this topic is typically approached — not medical advice.

Low or borderline B12 in someone with cognitive, neurological, or anaemic symptoms is a treatable finding that should be corrected. A normal level does not by itself exclude functional deficiency if suspicion is high.

• Serum B12
• Methylmalonic acid and/or homocysteine (to confirm functional deficiency)
• Checked routinely in cognitive workups

B12 deficiency is an established, reversible cause of neurological and cognitive symptoms; correcting it is well supported. Supplementation in replete people does not improve cognition, and B-vitamin homocysteine-lowering has not prevented cognitive decline in trials.

• Hematology and neurology guidance on B12 deficiency
• Homocysteine-lowering trial meta-analyses (null for cognitive prevention)

Sources are named authoritative guidelines and scientific bodies. Biomarker pages present established clinical context; calibrated evidence verdicts on specific interventions live in the linked Signal Records.