Vitamin B12 status in vegans compared to vegetarians and omnivores
What it found
Vegan adults had lower vitamin B12 status than omnivores, based on blood markers.
Vitamin B12 supplements improved these markers in vegans.
What they found
Studies in people
Serum B12 levels
Vegans had lower serum B12 levels than omnivores and vegetarians. The average serum B12 was 249.4 pmol/L in vegans, 252 pmol/L in vegetarians and 384.9 pmol/L in omnivores.
Homocysteine levels
Vegans had higher total homocysteine levels than omnivores and vegetarians. The average was 13.4 μmol/L in vegans, 12.5 μmol/L in vegetarians and 9.7 μmol/L in omnivores.
Methylmalonic acid levels
Vegans had higher methylmalonic acid levels than omnivores, but the difference was not significant. The average was 269 nmol/L in vegans and 180.5 nmol/L in omnivores.
Holotranscobalamin levels
Vegans had lower holotranscobalamin levels than omnivores, but the difference was not significant. The average was 62.9 pmol/L in vegans and 75.5 pmol/L in omnivores.
Supplement use in vegans
Vegans who used vitamin B12 supplements had better biomarker levels than those who did not. Supplement users had higher serum B12 and holotranscobalamin, and lower methylmalonic acid and homocysteine.
What the authors conclude
“Our findings underscore the need for improved strategies to redress poor vitamin B12 status with appropriate B12 supplementation use among those adhering to vegetarian and vegan diets.”
Also in their conclusions
- They conclude that vegans have lower vitamin B12 status than vegetarians and omnivores, based on both static and functional markers.
- They advise that vitamin B12 supplements are a simple and effective way to reduce the risk of deficiency in vegans.
- They recommend regular monitoring of vitamin B12 status using multiple biomarkers and appropriate supplementation for those on plant-based diets.
How it was done
The authors wanted to test whether a vegan diet is linked to a higher risk of functional vitamin B12 deficiency compared to vegetarian or omnivorous diets, using a full panel of biomarkers.
They searched three databases and found 19 studies that met their criteria, including 930 vegans, 1019 vegetarians and 1166 omnivores. They combined data from 17 studies in a meta-analysis and looked at supplement use in 4 studies.
What it can’t tell you
- The studies included were mostly observational, so they can show links but not prove that a vegan diet causes vitamin B12 deficiency.
- The review included only Caucasian adults, so the findings may not apply to other groups.
- The effect of vitamin B12 supplements was based on only 4 studies, so more research is needed.
Who paid
- Funding
- Funded by Biotechnology and Biological Sciences Research Council (from the PubMed record).
- Authors work at
- University of Surrey, UK; University of Freiburg, Germany; Quadram Institute Bioscience, UK
The paper
- Title
- A systematic review and meta-analysis of functional vitamin B12 status among adult vegans
- Type
- Systematic review and meta-analysisThe authors follow a set, published method to find every relevant study, then combine the numbers from them into one result.
- Evidence
- Studies in people
- Summarised from
- Full text
- Cite
- Niklewicz A, Hannibal L, Warren M, Ahmadi KR (2024). A systematic review and meta-analysis of functional vitamin B12 status among adult vegans. Nutrition bulletin. doi:10.1111/nbu.12712Free full textPubMed 39373282DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error