Supplements · Diets
plant-based diet increases vitamin B12 deficiency risk
In plain terms: Do vegans risk low B12 (high homocysteine/MMA) without supplements?
Part of: 🥗 plant-based diet
Yes — this is well established: unsupplemented vegans show low serum B12, low holoTC and elevated homocysteine/MMA; supplementation corrects it.
Evidence ladder
How far up the ladder this claim has climbed. A high consensus on a low rung means "consistent so far," not "proven in people."
Top evidence so far: All trials, pooled (Meta-analysis)
How the studies fall
The evidence (12)
| Source | Grade | Stance | Quality | Finding |
|---|---|---|---|---|
| Pawlak 2013 · Nutr Rev | observational | supports | moderate | MMA/holoTC-based review: high depletion/deficiency across vegetarians regardless of demographics; worse in vegans. |
| Henjum 2023 · Br J Nutr | observational | supports | moderate | Plant-based diet study finds increased risk of inadequate B12 status via biomarkers. |
| Jensen 2023 · Nutr Rev | meta-analysis | supports | moderate | Meta-analysis in children/adolescents on plant-based diets: significantly lower B12 status, risk of deficiency and growth harm without supplementation. |
| Lederer 2019 · Nutrients | RCT | supports | moderate | RCT of short-term vegan diet in healthy adults shows measurable decline in B12 status markers. |
| Herrmann 2005 · Clin Lab | observational | supports | moderate | Low holoTC in 76% of vegans and elevated MMA with low holoTC in 64%, confirming dietary B12 deficiency. |
| Barebring 2023 · Food Nutr Res | meta-analysis | supports | high | Systematic review concludes habitual dietary B12 is insufficient to ensure adequate status in susceptible groups including vegetarians/vegans. |
| Pawlak 2016 · Eur J Clin Nutr | meta-analysis | supports | moderate | Review of literature finds high prevalence of cobalamin deficiency among vegetarians/vegans assessed by serum B12. |
| Storz 2024 · Nutrition | n-of-1 | supports | low | Close-interval case study: a healthy vegan's B12 status declined measurably after stopping supplements, illustrating dependence on supplementation. |
| Niklewicz 2024 · Nutr Bull | meta-analysis | supports | high | Meta-analysis (17 studies): vegans had lower serum B12 and holoTC and higher homocysteine/MMA than omnivores; supplementation normalized biomarkers. |
| Pawlak 2014 · Eur J Clin Nutr | observational | supports | moderate | Systematic review of 40 studies: deficiency reaches 45% in infants and up to 86.5% in adults, higher in vegans. |
| Herrmann 2009 · Clin Chem Lab Med | observational | supports | moderate | Vegetarians show elevated homocysteine/MMA and low holoTC reflecting functional B12 deficiency affecting bone metabolism. |
| Janko 2025 · Am J Health Promot | meta-analysis | supports | moderate | Meta-analysis of Seventh-day Adventist vegans/vegetarians: lower B12 intake and serum levels vs omnivores, higher deficiency susceptibility. |
Disagree, or know a study we missed?
We grade by evidence, not opinions. The way to weigh in is to point us to a study we haven't cited (check the evidence table above first), or to flag a problem with one we have. Every submission is reviewed; if it holds up, the grade updates and shows in Science Changes Its Mind.
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Educational only, not medical advice. Grades and scores reflect published evidence weighted by study design and quality; see the methodology.