Vitamin B12 Supplementation: Is More Always Better?

2026-05-18
Nutrients 18(10)
- Manuela Yepes-Calderón
- Caecilia S E Doorenbos
- Mariken E Stegmann
- Daan J Touw
- Hermie J M Harmsen
- M Rebecca Heiner-Fokkema
- Francjan J van Spronsen
- Eva Corpeleijn
- Stephan J L Bakker

PubMed: 42197057
DOI: 10.3390/nu18101597

Study Design

Type: Review
Population: general populations of high-income countries (~2%), settings with limited access to animal-source foods or B12-fortified products (up to 69%)
Methods: We present guidance from major health authorities, advises against routine testing in asymptomatic individuals without risk factors. Studying the effects of supplementation challenged by variation in regimens, range from 0.02 to 1 mg/day orally and from 1 to 5 mg/week intramuscularly, durations spanning ~4 weeks to ~7 years
Duration: ~4 weeks to ~7 years

Rigorous Journal

Vitamin B₁₂ supplementation among people without proven deficiency has become popularized, driven by perceptions of (i) frequent underdiagnosis of deficiency, (ii) promotion as a natural enhancer of well-being, and (iii) a favourable safety profile. Here, we examine whether these claims align with current evidence. We present guidance from major health authorities, which advises against routine testing in asymptomatic individuals without risk factors. The prevalence of B₁₂ deficiency varies greatly, mainly because definitions of B₁₂ deficiency are not standardized and may include clinical, biochemical, or functional criteria. Biochemical deficiency (typically serum B₁₂ < 148 pmol/L) is the predominant definition in epidemiological and clinical research studies. Using this criterion, deficiency appears uncommon in general populations of high-income countries (~2%), but substantially more frequent in settings with limited access to animal-source foods or B₁₂-fortified products (up to 69%). Studying the effects of supplementation is also challenged by variation in the regimens used, which range from 0.02 to 1 mg/day orally and from 1 to 5 mg/week intramuscularly, with durations spanning ~4 weeks to ~7 years. This limits cross-study comparability. Overall, supplementation has not shown consistent benefits in populations without overt clinical or biochemical B₁₂ deficiency, with no clear improvements in fatigue, mood, cognition, or cardiovascular outcomes. Benefits, when reported, appear confined to selected subgroups (e.g., hyperhomocysteinemia or low-normal B₁₂ status). B₁₂ supplementation is generally well tolerated. There are rare reports of acneiform and hypersensitivity responses, although these cannot be completely distinguished from reactions to, e.g., excipients. Observational studies associate B₁₂ supplementation and higher circulating B₁₂ levels with increased risks of malignancy. However, these findings are inconsistent, and current evidence is insufficient to establish causality, as potential reverse causation remains a major concern.

Research Insights

Vitamin B12→Improved Cognition
Overall, supplementation has not shown consistent benefits in populations without overt clinical or biochemical B12 deficiency, with no clear improvements in fatigue, mood, cognition, or cardiovascular outcomes.
Effect
Neutral
Effect size
Small
Dose
0.02 to 1 mg/day orally and 1 to 5 mg/week intramuscularly, durations ~4 weeks to ~7 years
Vitamin B12→Improved Mood
Overall, supplementation has not shown consistent benefits in populations without overt clinical or biochemical B12 deficiency, with no clear improvements in fatigue, mood, cognition, or cardiovascular outcomes.
Effect
Neutral
Effect size
Small
Dose
0.02 to 1 mg/day orally and 1 to 5 mg/week intramuscularly, durations ~4 weeks to ~7 years
Vitamin B12→Reduced Cardiovascular Event Rate
Overall, supplementation has not shown consistent benefits in populations without overt clinical or biochemical B12 deficiency, with no clear improvements in fatigue, mood, cognition, or cardiovascular outcomes.
Effect
Neutral
Effect size
Small
Dose
0.02 to 1 mg/day orally and 1 to 5 mg/week intramuscularly, durations ~4 weeks to ~7 years
Vitamin B12→Reduced Fatigue
Overall, supplementation has not shown consistent benefits in populations without overt clinical or biochemical B12 deficiency, with no clear improvements in fatigue, mood, cognition, or cardiovascular outcomes.
Effect
Neutral
Effect size
Small
Dose
0.02 to 1 mg/day orally and 1 to 5 mg/week intramuscularly, durations ~4 weeks to ~7 years

Adverse Events Reported

Vitamin B12→Overall tolerability
B12 supplementation is generally well tolerated.
Finding
Reported
Vitamin B12→acneiform
There are rare reports of acneiform and hypersensitivity responses, although these cannot be completely distinguished from reactions to, e.g., excipients.
Finding
Reported
Vitamin B12→hypersensitivity
There are rare reports of acneiform and hypersensitivity responses, although these cannot be completely distinguished from reactions to, e.g., excipients.
Finding
Reported
Vitamin B12→malignancy
Observational studies associate B12 supplementation and higher circulating B12 levels with increased risks of malignancy. However, these findings are inconsistent, and current evidence is insufficient to establish causality, as potential reverse causation remains a major concern.
Finding
Reported