Evidence brief · Supplement
Vitamin B12 for Cognitive decline
Evidence grade C — Corrects deficiency-linked decline only
- Overall grade
- Grade C
- Last revised
- 1
- graded outcome
- 0
- references listed
Assembled by the app from other entries in this library. It adds no evidence of its own — follow the links to the entries it draws on.
1 at grade C — 1 graded row
What is known
Each outcome with its grade (how strong the evidence is, A to D), the size of the effect where the entry records one, and how often studies agree.
- Cognitive declineEvidence grade C
Corrects deficiency-linked decline only
Unclearmixed
What is uncertain
Read off the same rows as above. Nothing here is added that the entry does not itself record.
- Thin evidence: Cognitive decline (grade C).
The evidence in words
The verdict
For cognitive decline, Vitamin B12 earns evidence grade C (unclear effect, mixed consistency) — the evidence is limited or mixed. Corrects deficiency-linked decline only
How it might work
B12 is a cofactor for two enzymes: methionine synthase (regenerating methionine and folate, tying it to homocysteine and methylation) and methylmalonyl-CoA mutase. Absorption is a multi-step process requiring stomach acid and intrinsic factor — which is why acid-suppressing drugs and gastric/ileal disease impair it.
How to use it
For maintenance in vegans, 50–250 µg/day oral (or 1,000 µg a few times weekly) works because passive absorption covers a fraction of large doses. Confirmed deficiency with neurological signs is a medical matter and often treated with injections. Methylcobalamin and cyanocobalamin are both effective.
Safety & cautions
Exceptionally safe with no established toxicity; excess is excreted. The real danger is under-treatment. High-dose folate can mask the anemia of B12 deficiency while nerve damage progresses — test B12 status, don't just chase the blood count.
Bottom line
If you eat little or no animal food, or take metformin or a PPI long-term, supplement B12 or test — the downside of deficiency (permanent nerve damage) is far worse than the trivial cost of prevention.
How it is used
As the entry records it, from the studies it summarises. Not a recommendation for you — doses that suit a trial population may not suit you.
- Vegan maintenance
- 50–250 µg/day, or 1,000 µg 2–3×/week.
- Deficiency
- Medical management; often injections initially.
Goes with
- Vitamin B12Read the full Vitamin B12 monographEvidence grade A
Related reading
Entries that share this one's tags or conditions.
- Vitamin B12 for Correcting deficiency / anemiaEvidence grade A — DefinitionalEvidence grade A
- Vitamin B12 for Energy in replete peopleEvidence grade D — No effect without deficiencyEvidence grade D
- Vitamin B12 for Neuropathy (early deficiency)Evidence grade A — Reversible if caught earlyEvidence grade A
- Vitamin B12 for Pernicious / macrocytic anemiaEvidence grade A — Standard treatmentEvidence grade A
Sources
This entry lists no references of its own — it is assembled from the entries it links to, whose sources are on their pages.
Last revised . A grade is this entry's reading of the evidence, not medical advice.