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Dr. Grey AI

Supplement

Vitamin B12

Vitamin B12 is a vitamin the body needs to keep nerves working, build red blood cells and make DNA, and the risk of running low rises with age. People mostly look at it for low B12 levels, where the evidence is strong, though trials measuring thinking and memory in that group found no clear difference. Studies of depression symptoms also found no clear difference, and the evidence there is very limited.

Sources: PMID 33809274

Best evidence
Grade D
Conditions studied
6
Outcomes
18
Graded outcomes
0007

Evidence by condition

  • Strong
  • Moderate
  • Limited
  • Very limited

6 conditions

Depression

Depression: outcomes studied for Vitamin B12
GradeOutcomeEffectSizeStudiesPeopleStudies list
Depression Symptoms

No effect

NoneNo effect2 studies2,912 people

Studies that measured depression symptoms

Cognition

No effect

NoneNo effect2,912 people
Fatigue SymptomsImproves (the measure goes down)1 study2,912 people

Studies that measured fatigue symptoms

Stroke

Stroke: outcomes studied for Vitamin B12
GradeOutcomeEffectSizeStudiesPeopleStudies list
Depression Symptoms

No effect

NoneNo effect2 studies14 people

Studies that measured depression symptoms

Fatigue SymptomsImproves (the measure goes down)1 study14 people

Studies that measured fatigue symptoms

Stroke RecoveryImproves (the measure goes up)14 people

Vitamin B12 Deficiency

  • Cognition
  • Depression Symptoms: improves
  • Fatigue Symptoms: improves
Vitamin B12 Deficiency: outcomes studied for Vitamin B12
GradeOutcomeEffectSizeStudiesPeopleStudies list
Cognition

No effect

NoneNo effect2,912 people
Depression SymptomsImproves (the measure goes down)2 studies2,912 people

Studies that measured depression symptoms

Fatigue SymptomsImproves (the measure goes down)1 study2,912 people

Studies that measured fatigue symptoms

HomocysteineImproves (the measure goes down)1 study100 people

Studies that measured homocysteine

Age Associated Memory Impairment And Cognitive Decline Aamcd

  • Cognition
  • Depression Symptoms: improves
  • Fatigue Symptoms: improves
Age Associated Memory Impairment And Cognitive Decline Aamcd: outcomes studied for Vitamin B12
GradeOutcomeEffectSizeStudiesPeopleStudies list
Cognition

No effect

NoneNo effect2,912 people
Depression SymptomsImproves (the measure goes down)2 studies2,912 people

Studies that measured depression symptoms

Fatigue SymptomsImproves (the measure goes down)1 study2,912 people

Studies that measured fatigue symptoms

Schizophrenia

  • Cognition
  • Schizophrenia symptoms: improves
Schizophrenia: outcomes studied for Vitamin B12
GradeOutcomeEffectSizeStudiesPeopleStudies list
Cognition

No effect

NoneNo effect55 people
Schizophrenia symptomsImproves (the measure goes down)55 people

Age-Associated Memory Impairment and Cognitive Decline (AAMCD)

  • Cognition
  • Depression Symptoms: changes; see studies
  • Fatigue Symptoms: changes; see studies
Age-Associated Memory Impairment and Cognitive Decline (AAMCD): outcomes studied for Vitamin B12
GradeOutcomeEffectSizeStudiesPeopleStudies list
Cognition

No effect

NoneNo effect2,912 people
Depression SymptomsChanges; see studies2 studies2,912 people

Studies that measured depression symptoms

Fatigue SymptomsChanges; see studies1 study2,912 people

Studies that measured fatigue symptoms

What the published studies found

2 automated readings

Automated reading of the published studies (Decosa evidence engine), for outcomes Dr. Grey has not graded yet. It is not a Dr. Grey grade and does not change one. How it is read

  • Fatigue

    The studies read are too weak to tell whether Vitamin B12 changes fatigue. The evidence is very weak.

    1 study counted of 11 read: 1 trial (15 people in the trials).
    1. Crossover trial, 1989; 15 people; patients with chronic fatigue syndrome: no clear difference. no significant difference was apparent between response to placebo Liver extract-folic acid-cyanocobalamin vs placebo for chronic fatigue syndromePubMed 2684076

    Automated reading of the published studies (Decosa evidence engine), run 30 Sep 2026. It reads abstracts, can miss studies, and a repeat run can differ.

  • Muscle soreness

    Too few usable studies were found to tell whether Vitamin B12 changes muscle soreness. 8 studies were read and none could be counted.

    Side effects: 1 of the 3 studies that reported on them found more with Vitamin B12 (muscle pain).

    Automated reading of the published studies (Decosa evidence engine), run 30 Sep 2026. It reads abstracts, can miss studies, and a repeat run can differ.

Key findings

  • Depression SymptomsDepression
  • CognitionDepression

Shop Vitamin B12

Third-party tested Vitamin B12 products. The evidence above is limited, so read it before you buy.

  • Grade D

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Studies cited

5 studies from PubMed

  1. Folate and vitamin B12 supplementation in patients with schizophrenia and low serum folate level: A 24-week randomized, double-blind, placebo-controlled study.J Formos Med Assoc · PMID 39645464
  2. Effects of vitamin B12 supplementation on cognition, depression, and fatigue in patients with lacunar strokeInt Psychogeriatr · PMID 23158866
  3. A vitamin B-12 supplement of 500 μg/d for eight weeks does not normalize urinary methylmalonic acid or other biomarkers of vitamin B-12 status in elderly people with moderately poor vitamin B-12 statusJ Nutr · PMID 23236022
  4. Effects of Vitamin B12 Supplementation on Cognitive Function, Depressive Symptoms, and Fatigue: A Systematic Review, Meta-Analysis, and Meta-Regression.Nutrients · PMID 33809274
  5. Systematic review and meta-analysis of randomized placebo-controlled trials of folate and vitamin B12 for depression.Int Psychogeriatr · PMID 25644193

Protocols that include Vitamin B12