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.
📅 Last reviewed: 2026-07-15 ⓘ
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
What the evidence shows
Unsupplemented plant-based diets reliably lower vitamin B12 status: low holotranscobalamin in 76 percent of vegans in one series, elevated methylmalonic acid in 64 percent, a measurable decline within a short randomised vegan trial, and lower status in children and adolescents. Supplementation corrects it, and supplementing vegans often have the highest levels of all.
The evidence (13)
| Source | Grade | Stance | Quality | Finding |
|---|---|---|---|---|
| Bell W et al 2026 · medRxiv | observational | mixed | moderate | UK FEED cross-sectional (n=633): B12 highest in vegans overall (many supplemented); non-supplementing vegans/vegetarians had lower but not deficient B12 vs omnivores. |
| Pawlak R, Parrott SJ, Raj S, Cullum-Dugan D, Lucus D 2013 · Nutr Rev | observational | supports | moderate | MMA/holoTC-based review: high depletion/deficiency across vegetarians regardless of demographics; worse in vegans. |
| Henjum S, Groufh-Jacobsen S, Lindsay A, Raael E, Israelsson AM, Shahab-Ferdows S, Hampel D 2023 · Br J Nutr | observational | mixed | moderate | Plant-based diet study finds increased risk of inadequate B12 status via biomarkers. |
| Jensen CF 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 AK, Hannibal L, Hettich M, Behringer S, Spiekerkoetter U, Steinborn C, Gründemann C, Zimmermann-Klemd AM, Müller A, Simmet T, Schmiech M, Maul-Pavicic A, Samstag Y, Huber R 2019 · Nutrients | RCT | supports | moderate | RCT of short-term vegan diet in healthy adults shows measurable decline in B12 status markers. |
| Herrmann W, Obeid R, Schorr H, Geisel J 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 | observational | supports | moderate | Systematic review concludes habitual dietary B12 is insufficient to ensure adequate status in susceptible groups including vegetarians/vegans. |
| Pawlak R, Lester SE, Babatunde T 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 MA, Huber R, Hannibal L 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 A, Hannibal L, Warren M, Ahmadi KR 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 R, Lester SE, Babatunde T 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 W, Obeid R, Schorr H, Hübner U, Geisel J, Sand-Hill M, Ali N, Herrmann M 2009 · Clin Chem Lab Med | observational | supports | moderate | Vegetarians show elevated homocysteine/MMA and low holoTC reflecting functional B12 deficiency affecting bone metabolism. |
| Janko RK, Haussmann I, Patel A 2025 · Am J Health Promot | meta-analysis | contradicts | moderate | Meta-analysis of 4 observational studies (1,994 participants) comparing vegan/vegetarian Seventh-day Adventists with omnivore controls. No significant difference in serum B12 (MD -9.85 pmol/L, 95% CI -45.64 to 25.94, P=0.54, I2 50%) or B12 intake (MD +3.31 mcg/d, 95% CI -4.70 to 11.32, P=0.42, I2 90%). Authors: plant-based Adventists 'did not demonstrate increased risk of vitamin B12 deficiency due to the widespread consumption of fortified foods and supplements.' Null in a heavily supplemented/fortified population; only 4 studies, high heterogeneity; deficiency prevalence itself not pooled. Abstract only. (Prior extract stated the opposite result.) |
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