In the British EPIC-Oxford cohort, 52% of vegan men had blood vitamin B12 levels below the deficiency threshold set by researchers, compared to 7% of vegetarians and only one omnivore out of 226. This figure above all reminds us that vitamin B12 deficiency is preventable.
This guide brings together what studies identified via PubMed show: the frequency of deficiencies, the real value of algae, spirulina and fermented foods, fortified foods, blood markers, doses studied in supplementation, pregnancy, childhood and advanced age, then other nutrients to monitor.
The findings : reviews find frequent deficiencies in vegetarians and especially in vegans without supplementation, up to 86.5% in adults according to studies. Spirulina contains mainly an inactive form, and mushrooms and fermented foods have low or variable levels. In vegans who supplement, deficiencies become rare.
What helps : a regular source, supplement or fortified foods, and a blood test combining vitamin B12, holotranscobalamin, methylmalonic acid and homocysteine. In vegans and vegetarians with mild deficiency, 50 µg per day corrected markers, with no significant difference from 2,000 µg per week. Pregnancy, breastfeeding and early childhood require medical monitoring.
- Why vitamin B12 is lacking in plant-based diets
- How many deficiencies among vegetarians and vegans
- When supplements are in place: reassuring results
- Algae, spirulina, mushrooms, fermented foods: what the analyses show
- Fortified foods and other sources of intake
- Blood markers to monitor
- What dose of B12 for a vegan: what trials tested
- Pregnancy and breastfeeding: published cases in infants
- Children, adolescents and elderly people
- Vitamin D, iodine, iron, zinc, omega-3: other nutrients to monitor
- Frequently asked questions
Why vitamin B12 is missing from plant-based diets
Vitamin B12, or cobalamin, is produced solely by certain bacteria. It then accumulates in animal tissues, especially in those positioned higher in the food chain: meat, milk, eggs, fish, and shellfish are its usual sources. It is the only vitamin absent from plant foods, with rare exceptions.
Dairy products and eggs, consumed by vegetarians, provide little according to a review on plant-based sources: milk contains approximately 0.3 to 0.4 µg per 100 g, and a significant portion is lost during processing; eggs contain 0.9 to 1.4 µg per 100 g, mainly in the yolk, with bioavailability of only 3.7 to 9.2% after cooking.
The liver stores 1 to 1.5 mg of vitamin B12 according to a review on vegetarians, which explains why deficiency develops slowly. The idea that it would only appear after many years is called a myth by its authors. Our complete vitamin B12 guide details its roles and signs of deficiency; this article focuses on plant-based nutrition.
Studies distinguish the vegetarian who consumes dairy products and eggs (lacto-ovo-vegetarian) from the vegan, who excludes all animal products. The risk exists in both cases, significantly more pronounced in vegans.
How many deficiencies among vegetarians and vegans
A review published in 2014 compiled 40 studies measuring blood vitamin B12 in vegetarians. The frequency of deficiency reached 45% in infants, 0 to 33.3% in children and adolescents, 17 to 39% in pregnant women depending on trimester, and 0 to 86.5% in adults and elderly people. Vegans without supplements formed the most at-risk group.
Blood vitamin B12 is, however, only an imperfect reflection. An earlier review by the same team was limited to 18 studies that measured more sensitive markers, methylmalonic acid and holotranscobalamin: deficiency affected 62% of pregnant women, 25% to nearly 86% of children, 21 to 41% of adolescents, and 11 to 90% of elderly people. It was more frequent in vegans and in vegetarians since birth.
Among 689 men from the EPIC-Oxford cohort, average blood vitamin B12 was 281 pmol/L in omnivores, 182 pmol/L in vegetarians, and 122 pmol/L in vegans. With a threshold of 118 pmol/L, 52% of vegans and 7% of vegetarians were classified as deficient. Neither age nor duration of the diet were associated with this.
Gilsing AM, Crowe FL, Lloyd-Wright Z, et al. Eur J Clin Nutr 2010;64(9):933-939. DOI: 10.1038/ejcn.2010.142
A 2024 meta-analysis combined 17 studies. Compared to omnivores, adult vegans had significantly lower blood vitamin B12 (effect size of −0.72) and higher homocysteine (0.57), with a non-significant trend for methylmalonic acid (0.28) and holotranscobalamin (−0.42). Vegans taking a vitamin B12 supplement had better results on all markers than those who did not.
Meta-analyses often express their results in effect size, which relates the difference between two groups to the spread of measurements. By convention, 0.2 corresponds to a small effect, 0.5 to a medium effect, and 0.8 to a large effect: the difference of 0.72 falls between medium and large.
| Population | Frequency of deficiency | Level of evidence (editorial assessment) |
|---|---|---|
| Vegan men, British cohort | 52%, compared to 7% of vegetarians | Solid for this population, single measurement |
| Adult and elderly vegetarians, 40 studies | 0 to 86.5% depending on studies | Large review, highly dispersed results |
| Pregnant vegetarian women | 17 to 39% (blood vitamin B12), 62% (sensitive markers) | Moderate, few studies |
| Adult vegans, meta-analysis of 17 studies | Lower vitamin B12, higher homocysteine than in omnivores | Strong evidence for vitamin B12 and homocysteine |
When supplements are in place: reassuring results
In Switzerland, a study compared 100 omnivores, 53 vegetarians and 53 vegans aged 18 to 50 years: despite vitamin B12 dietary intake being nearly zero in vegans, deficiency remained rare in all groups, thanks to widespread use of supplements.
In 36 German vegans and 36 omnivores aged 30 to 60 years, almost all vegans were taking supplements. Vitamin B12 markers did not differ between the two groups, whereas vegans consumed almost none through diet. The authors attribute this good status to the high rate of supplementation.
Weikert C, Trefflich I, Menzel J, et al. Dtsch Arztebl Int 2020;117(35-36):575-582. DOI: 10.3238/arztebl.2020.0575
The same finding emerges from a meta-analysis of 4 studies and 1,994 participants among Seventh-day Adventists, a community some of whom follow a vegetarian or vegan diet: no significant difference in blood vitamin B12 (mean difference of −9.85 pmol/L) or intake compared with omnivores.
A German randomized trial conversely shows how rapid the phenomenon is when no source is provided. In 53 healthy omnivores, 4 weeks of vegan diet without supplementation lowered blood vitamin B12 and holotranscobalamin compared to a meat-rich diet, whereas methylmalonic acid and homocysteine remained stable over this period.
Deficiency is not an inevitable consequence of plant-based eating: it depends primarily on a regular source, whether supplement or fortified foods.
Seaweed, spirulina, mushrooms, fermented foods: what the analyses show
The first pitfall is analytical: microbiological assays also detect related compounds that are inactive in humans. According to a review dedicated to plant-based sources of vitamin B12 (2014), supplements based on blue-green algae often contain large quantities of pseudovitamin B12, inactive in humans.
In edible green and purple algae and in chlorella tablets, true vitamin B12 predominated, and the purple algae improved the status of deficient rats. In spirulina tablets, pseudovitamin B12 predominated, which is inactive: the authors consider them unsuitable as a source for vegetarians.
Watanabe F, Takenaka S, Kittaka-Katsura H, et al. J Nutr Sci Vitaminol 2002;48(5):325-331. DOI: 10.3177/jnsv.48.325
According to a 2016 review, spirulina displays 127 to 244 µg of "vitamin B12" per 100 g dry weight, of which approximately 80% are non-vitamin compounds.
The nori, the dried purple seaweed used in sushi, is an exception: it contains active vitamin B12, approximately 32.3 µg per 100 g dry weight, and the authors estimate that approximately 4 g of nori at 77.6 µg per 100 g covers the 2.4 µg daily requirement they consider necessary for adults. Two caveats: in the laboratory, its vitamin B12 is released at 50% under normal gastric acidity, but at 2.5% under severe atrophic gastritis conditions; and human data are limited to 6 Japanese vegan children who ate 2 to 4 g per day, with no difference in blood vitamin B12 compared with controls, while another study cited by the 2016 review found no benefit from nori and spirulina in deficient children.
The mushrooms disappoint: dried porcini, oyster and morel mushrooms contain only traces. Dried shiitake contains on average 5.61 µg per 100 g, ranging from 1.3 to 12.7 µg depending on samples, and approximately 50 g per day would be needed, a quantity considered unrealistic by the authors.
The fermented foods depend on bacteria present by chance. Tempeh contains 0.7 to 8.0 µg per 100 g according to the review on plant-based sources, but another analysis detected only 0.16 to 0.72 µg per kilo (0.016 to 0.072 µg per 100 g), and nothing in tofu; kimchi contains less than 0.1 µg per 100 g.
In 17 vegans and vegetarians whose methylmalonic acid exceeded 270 nmol/L, the addition of 9 g per day of commercial chlorella over 60 days reduced methylmalonic acid by approximately 34% on average; blood vitamin B12 and homocysteine evolved in the right direction without reported significant change, and blood parameters for anemia remained stable.
Merchant RE, Phillips TW, Udani J. J Med Food 2015;18(12):1357-1362. DOI : 10.1089/jmf.2015.0056
This result remains limited: no control group, small sample size, single product, and B12 content ranging from zero to several hundred µg per 100 g depending on the chlorella tablets.
| Food | What the analyses show | Reliability as a source (editorial assessment) |
|---|---|---|
| Spirulina | Mostly pseudovitamin B12, inactive in humans; approximately 80% of the total non-vitamin form | Not reliable |
| Nori (dried purple seaweed) | Active vitamin B12, 32.3 to 77.6 µg per 100 g dry weight depending on the products | Promising, limited human data |
| Chlorella | Active form, but ranging from zero to several hundred µg per 100 g depending on the tablets | Too variable |
| Dried shiitake | 1.3 to 12.7 µg per 100 g dry weight, mostly active form | Insufficient at typical serving sizes |
| Tempeh | From 0.016 to 8.0 µg per 100 g depending on analyses | Unpredictable |
Fortified foods and other intake sources
Fortified foods use crystalline vitamin B12, free from any protein, the same as in supplements, which does not require gastric acidity to be released. The review on plant-based sources cites studies in elderly individuals where cereals fortified with folic acid and vitamins B6 and B12 increased their blood levels and lowered homocysteine. The limitation lies in regularity: according to the 2016 review, the amounts added vary considerably, fortified nutritional yeast may be less effective than a supplement in case of deficiency, and a deficiency can develop within five years despite fortified foods.
A more unexpected approach was tested: fortified toothpaste. Over 12 weeks, in a double-blind study, 76 vegans used toothpaste fortified with vitamin B12 or a placebo, and 66 completed the study. In the fortified group, blood vitamin B12 increased by an average of 81 pmol/L and holotranscobalamin by 26 pmol/L, compared to decreases of 27 and 5 pmol/L under placebo; methylmalonic acid decreased further, and homocysteine showed only a trend (p = 0.051). This is a promising lead, not a validated strategy.
Blood markers to monitor
Total blood vitamin B12 is the standard test, but its predictive value is low. Deficiency thresholds vary depending on laboratories and studies, from less than 118 pmol/L in the EPIC-Oxford cohort to less than 250 pmol/L in other studies, and a deficiency may already exist above 156 pmol/L, a frequently used threshold, according to the 2016 review.
Three other markers refine the diagnosis. Theholotranscobalamin, the portion of vitamin B12 actually delivered to cells, is considered more reliable; the most commonly used sufficiency threshold is above 35 pmol/L. Themethylmalonic acid accumulates when vitamin B12 is lacking in cells, with thresholds of 271 to 376 nmol/L depending on studies. Thehomocysteine also rises, with thresholds of 10, 12 or 15 µmol/L, but also depends on folates and vitamin B6. Renal insufficiency elevates these two markers: creatinine helps interpret them.
Plant-based diets are rich in folates, the highest levels being in vegans in the EPIC-Oxford cohort. The review on plant-based sources notes that this abundance can mask a vitamin B12 deficiency until serious problems appear, and a review dedicated to vegetarians notes that neurological signs can occur without anemia. A normal blood count is therefore not sufficient to rule out a deficiency.
For a person with normal test results who has other sources (dairy products, eggs, fortified foods), our B Vitamins combines all 8 B vitamins in one capsule, including 2.5 µg of vitamin B12 in methylcobalamin form and 400 µg of vitamin B9 in active folate form. In case of abnormal markers, the course of action and dosage should be decided with a physician.
| Marker | What it measures | Thresholds cited in studies |
|---|---|---|
| Blood vitamin B12 | Total circulating vitamin B12, sensitive to recent intake | Less than 118 to less than 250 pmol/L depending on studies |
| Holotranscobalamin | Amount delivered to cells, responds within weeks | Sufficiency above 35 pmol/L |
| Methylmalonic acid | Deficiency inside cells | Above 271 to 376 nmol/L |
| Homocysteine | Vitamin B12, folate, or vitamin B6 deficiency | Above 10, 12, or 15 µmol/L |
What dose of B12 for a vegan: what trials tested
It all comes down to absorption. The active mechanism, via intrinsic factor produced by the stomach, is limited to approximately 1.5 to 2 µg per meal. Passive diffusion, independent of this factor, allows about 1% of the dose to enter; it becomes significant with high doses of 0.5 to 1 mg. According to data compiled in the 2016 review, a dose of 1 µg is absorbed at 56%, 10 µg at 16%, 50 µg at 3%, 500 µg at 2%, and 1,000 µg at 1.3%.
Hence two strategies: a small daily dose, or a high dose spaced out. The 2016 review suggests that a dose of 50 to 100 µg per day, or 2,000 µg per week in two doses of cyanocobalamin, could meet the 2.4 µg daily requirement of a healthy vegetarian adult, taking into account active and passive absorption.
In 40 vegans and vegetarians with mild deficiency, 12 weeks of sublingual cyanocobalamin at 350 µg per week, or 50 µg per day, or 2,000 µg once per week both restored blood vitamin B12, increased holotranscobalamin, and decreased methylmalonic acid and homocysteine. No difference appeared between the two doses, nor any effect on blood cell count.
Del Bo' C, Riso P, Gardana C, et al. Clin Nutr 2019;38(2):575-583. DOI: 10.1016/j.clnu.2018.02.008
Other trials used higher doses to correct established deficiency. In 120 elderly people with mild deficiency, oral cyanocobalamin at 2.5, 100, 250, 500, and 1,000 µg per day for 16 weeks reduced methylmalonic acid by 16, 16, 23, 33, and 33% respectively; 647 to 1,032 µg per day were needed to achieve 80 to 90% of maximum effect. In 50 vegetarians from Hong Kong, 70% of whom had vitamin B12 below 150 pmol/L, 500 µg per day for 12 weeks reduced homocysteine and improved arm artery dilation (from 6.3 to 6.9%), unlike placebo, with no change in blood pressure or cholesterol.
Our B Complex Vitamins provides 2.5 µg of vitamin B12 per capsule, in methylcobalamin form, along with the seven other B vitamins. This is an amount close to the 2.4 µg daily requirement adopted by the cited reviews, but the 2016 review estimates that a healthy vegetarian adult needs 50 to 100 µg per day to meet this requirement, accounting for absorption. This amount remains considerably lower than the 50 µg per day tested in vegans with mild deficiency, and the 500 to 1,000 µg doses used to correct established deficiency. No trial has tested our complex: these figures contextualize the quantities, they do not transfer any results. For a vegan without another source, or in case of proven deficiency, the dose should be discussed with a doctor or pharmacist, who can recommend a higher-dose vitamin B12 supplement alone.
Pregnancy and breastfeeding: published cases in infants
A German study followed 109 pregnant women, including 27 vegetarians consuming milk and eggs for at least 3 years, 43 low meat consumers and 39 controls. The association of low vitamin B12 and elevated homocysteine affected 22% of them, compared to 10% of low meat consumers and 3% of controls. The status improved significantly when dietary vitamin B12 intake approached 3 µg per day.
Breast milk then transmits the mother's vitamin B12. An American study of 74 milk samples from 26 vegan mothers, 22 vegetarian mothers and 26 omnivorous mothers provides a nuanced result: nearly one in five milk samples was low in vitamin B12 (less than 310 pmol/L), with no difference by diet (19.2%, 18.2% and 15.4%). A vitamin B12-only supplement was associated with richer milk, a multivitamin with poorer milk, and approximately 85% of mothers with poor milk were nevertheless taking supplements.
Published cases show what happens when maternal deficiency is not detected. In Italy, a 5-month-old infant exclusively breastfed by a vegan mother who said she took a multivitamin in the second and third trimesters was hospitalized for insufficient weight gain, hypotonia and drowsiness: hemoglobin at 4.7 g/dL, vitamin B12 at 57 pg/mL, ferritin at 4 ng/mL, delayed myelination on imaging. After treatment, he improved, but his development remained delayed seven months later. In Montpellier, a 10-month-old infant breastfed by a vegan mother presented with psychomotor delay and deficiencies in vitamins B12, K and D, like his mother; supplementation allowed neurological improvement. In Denmark, two other infants aged 10 and 12 months breastfed by vegan mothers presented with anemia and developmental delay, which regressed with cyanocobalamin.
In infants breastfed by vegetarian mothers with low reserves, symptoms appear in the second quarter of life: growth delay, lethargy, hypotonia, regression of developmental milestones, and abnormal movements in half of cases. If untreated, the deficiency can leave lasting neurological sequelae; the authors emphasize supplements for vegan women who are pregnant or breastfeeding.
Chalouhi C, Faesch S, Anthoine-Milhomme MC, et al. Pediatr Emerg Care 2008;24(8):538-541. DOI: 10.1097/PEC.0b013e318180ff32
For a vegetarian or vegan woman planning a pregnancy, who is pregnant or breastfeeding, vitamin B12 supplementation and its dosing are decided with the doctor or midwife, from the pregnancy planning stage. Our B Vitamins complex is not presented for these situations: its information sheet requests professional health advice before any use in pregnant or breastfeeding women. In the breastfed infant, any slowing of growth, any hypotonia or any regression of developmental milestones warrants consultation without delay.
Children, adolescents and elderly persons
In children, results depend on supplements. In those aged 5 to 18 years, a meta-analysis finds blood vitamin B12 lower by 97 pmol/L on average with a plant-based diet, a significant difference in vegans but not in vegetarians, and which disappears when total intake is considered. Another meta-analysis of 18 studies conversely finds higher levels in vegan children, due to supplements, with evidence of low to very low certainty.
The broadest synthesis combines 59 studies and 48,626 children: it finds an increased likelihood of vitamin B12 deficiency in vegan children, and lower intakes of vitamin B12, vitamin D and zinc in vegetarian children. A position statement from European pediatricians (10 articles, approximately 1,500 vegan children) considers vitamin B12 supplementation essential in vegan children and recommends regular monitoring of growth and nutritional status.
In 430 German children aged 1 to 3 years, mean vitamin B12 intake without supplements was 1.5 µg per day in omnivores, 0.6 µg in vegetarians and 0.2 µg in vegans. With supplements, vegan children averaged 73.8 µg per day. The authors identify vitamin D, iodine and docosahexaenoic acid as critical for all children, and certain B vitamins, calcium and iron additionally for vegetarian and vegan children.
Weder S, Keller M, Fischer M, et al. Eur J Nutr 2022;61(3):1507-1520. DOI: 10.1007/s00394-021-02753-3
In children, the dose is decided with the pediatrician; our B Vitamins complex is reserved for adults.
In the elderly, stomach acid secretion decreases, which reduces the release of vitamin B12 from foods and the production of intrinsic factor, while passive diffusion is preserved. In elderly vegetarians, the frequency of deficiency ranges from 11 to 90% according to a 2013 review. The trial conducted in elderly persons with mild deficiency illustrates the difficulty: 2.5 µg per day of cyanocobalamin reduced methylmalonic acid by only 16%, compared to 33% from 500 µg. This is why, with advancing age, regular dosing and medical advice on the dose become fully meaningful, especially since certain long-term medications, such as treatments for gastric acidity and perhaps metformin, may reduce absorption.
Vitamin D, iodine, iron, zinc, omega-3: other nutrients to monitor
According to a systematic review of 141 studies, intakes and markers of vitamin B12, vitamin D, iron, zinc, iodine and calcium are generally lower with a plant-based diet, while meat eaters more often lack fiber, folate and magnesium.
Vitamin D. In the EPIC-Oxford cohort, in 2,107 adults, mean blood vitamin D was 77.0 nmol/L in meat eaters and 55.8 nmol/L in vegans, whose dietary intake was only 0.7 µg per day. The difference reached 38% in winter compared to 20% in summer. For vegans, vitamin D3 from lichen is an option, which our article lichen or lanolin explains the difference with the form derived from sheep's wool.
No trial has tested our Plant-Based Vitamin D3 ; in pregnant or nursing women, it should be taken on the advice of a practitioner.
Iodine. A meta-analysis of 11 articles and 4,421 adults found the lowest median urinary iodine concentration in vegans (12.2 µg/L) and the lowest intake (17.3 µg per day), with no group reaching the optimal range of 100 to 200 µg/L. In the German study mentioned above, one-third of vegans had urinary iodine below 20 µg/L, the threshold for severe deficiency.
Iron. A meta-analysis of 24 cross-sectional studies shows lower ferritin averaging 29.71 µg/L in vegetarians, 61.88 µg/L in men and 17.70 µg/L in non-menopausal women. The authors note that excessively high iron is also a risk factor and recommend everyone monitor their status.
Zinc. A meta-analysis of 26 studies found zinc intake 0.88 mg per day lower and blood zinc 0.93 µmol/L lower in vegetarians, with a more marked difference in women and vegans. In the Swiss study, zinc deficiency was the most common deficiency in vegans, at 47%.
Omega-3. In 196 meat eaters, 231 vegetarians and 232 British vegans, blood levels of eicosapentaenoic acid and docosahexaenoic acid, long-chain omega-3s, were lower in vegetarians and vegans, with no link to how long they had followed the diet: production by the body appears to maintain low but stable levels.
| Nutrient | What the studies show | Level of Concern (editorial assessment) |
|---|---|---|
| Vitamin D | 55.8 nmol/L in vegans versus 77.0 in meat eaters | Especially in winter |
| Iodine | Median urinary iodine of 12.2 µg/L in vegans | High in vegans |
| Iron | Lower ferritin, especially in men | Monitor ferritin levels |
| Zinc | Intake and blood levels slightly lower | Moderate |
| Long-chain Omega-3 | Blood levels lower but stable | Moderate, consequences still poorly understood |
All 8 B vitamins in one vegetarian capsule per day, including 2.5 µg of vitamin B12 in methylcobalamine form, 400 µg of vitamin B9 in active folate form and 5 mg of vitamin B6 in pyridoxal-5-phosphate form. Take in the morning at breakfast with a large glass of water, in courses of 1 to 3 months renewable. For adults only.
See B VitaminsOur complete guide to vitamin B12 details its roles, signs of deficiency and foods that contain it.
Frequently Asked Questions
Should a vegan take vitamin B12?
Yes, according to all the reviews cited: plants don't produce it, and vegans without supplementation form the group most at risk of deficiency. In the EPIC-Oxford cohort, 52% of vegan men were below the deficiency threshold. With a supplement or fortified foods, recent studies find status comparable to omnivores.
Do vegetarians who eat eggs and dairy products lack B12?
They are less at risk than vegans, but not immune: in the EPIC-Oxford cohort, 7% of vegetarians were deficient, and in pregnant vegetarian women, 22% had both low vitamin B12 and elevated homocysteine.
What dose of vitamin B12 for a vegan?
In a trial of vegans and vegetarians with mild deficiency, 50 µg daily sublingually and 2,000 µg once weekly corrected the markers, with no significant difference between the two regimens. In case of confirmed deficiency, the dose is determined with a physician.
Does spirulina provide vitamin B12?
Not reliably. Analyses show that spirulina contains mainly pseudovitamin B12, an inactive form in humans: approximately 80% of the stated content corresponds to non-vitamin compounds.
Are nori and seaweeds a source of B12?
Nori, dried purple seaweed, contains active vitamin B12, ranging from 32.3 to 77.6 µg per 100 g dry weight depending on the product, and approximately 4 g could meet the daily requirement according to one review. Human data remains limited and contradictory.
What blood test should I get to check my B12 when vegetarian?
Blood vitamin B12 alone can provide false reassurance. Studies recommend pairing it with holotranscobalamin, the portion delivered to cells, sufficient above 35 pmol/L, methylmalonic acid, and homocysteine.
How long before B12 deficiency develops after becoming vegan?
Liver reserves, around 1 to 1.5 mg, delay symptoms, sometimes for years. But markers shift quickly: in a randomized trial, 4 weeks of vegan diet without supplementation was enough to lower holotranscobalamin. It's better to plan a source from the moment dietary change begins.
Should vegetarian women take vitamin B12 during pregnancy?
This should be discussed with the physician or midwife from the time pregnancy is being planned. Studies show frequent deficiencies in pregnant vegetarian women, and published cases describe infants breastfed by deficient vegan mothers with growth delay, hypotonia, and psychomotor delay.
Can a vegan child lack vitamin B12?
Yes, without supplementation: a meta-analysis of 59 studies finds increased likelihood of deficiency in vegan children, while another finds higher levels in supplemented children. European pediatricians consider supplementation essential and recommend regular monitoring, to be organized with the pediatrician.
What other nutrients should be monitored on a vegan diet?
Vitamin D, especially in winter, iodine, which vegans have the lowest intakes of, iron, to be checked via ferritin, zinc, and long-chain omega-3s, lower but stable.
Sources
The studies cited below were identified via PubMed.
- Gilsing AM, Crowe FL, Lloyd-Wright Z, et al. Serum vitamin B12 and folate concentrations in British omnivorous, vegetarian, and vegan men: cross-sectional analysis of the EPIC-Oxford cohort. European Journal of Clinical Nutrition, 2010;64(9):933-939. DOI
- Watanabe F, Yabuta Y, Bito T, Teng F. Plant-based sources of vitamin B12 for vegetarians. Nutrients, 2014;6(5):1861-1873. DOI
- Rizzo G, Laganà AS, Rapisarda AM, et al. Vitamin B12 in vegetarians: status, assessment, and supplementation. Nutrients, 2016;8(12):767. DOI
- Pawlak R, Lester SE, Babatunde T. Frequency of cobalamin deficiency in vegetarians assessed by serum vitamin B12: literature review. European Journal of Clinical Nutrition, 2014;68(5):541-548. DOI
- Pawlak R, Parrott SJ, Raj S, et al. How common is vitamin B12 deficiency among vegetarians? Nutrition Reviews, 2013;71(2):110-117. DOI
- Niklewicz A, Hannibal L, Warren M, Ahmadi KR. Systematic review and meta-analysis of functional vitamin B12 status in adult vegans. Nutrition Bulletin, 2024;49(4):463-479. DOI
- Schüpbach R, Wegmüller R, Berguerand C, et al. Micronutrient status and intakes among omnivores, vegetarians and vegans in Switzerland. European Journal of Nutrition, 2017;56(1):283-293. DOI
- Weikert C, Trefflich I, Menzel J, et al. Vitamin and mineral status in vegan diets. Deutsches Ärzteblatt International, 2020;117(35-36):575-582. DOI
- Janko RK, Haussmann I, Patel A. Vitamin B12 status of vegan and vegetarian Seventh-day Adventists: systematic review and meta-analysis of serum levels and intakes. American Journal of Health Promotion, 2025;39(1):162-171. DOI
- Lederer AK, Hannibal L, Hettich M, et al. Vitamin B12 status after a short intervention with a vegan diet: randomized controlled trial in healthy volunteers. Nutrients, 2019;11(11):2815. DOI
- Watanabe F, Takenaka S, Kittaka-Katsura H, et al. Characterization and bioavailability of vitamin B12 compounds from edible algae. Journal of Nutritional Science and Vitaminology, 2002;48(5):325-331. DOI
- Suzuki H. Serum vitamin B12 levels in young vegans consuming brown rice. Journal of Nutritional Science and Vitaminology, 1995;41(6):587-594. DOI
- Mo H, Kariluoto S, Piironen V, et al. Effect of soy processing on folate, vitamin B12 and isoflavone content and bioaccessibility in tofu and tempeh. Food Chemistry, 2013;141(3):2418-2425. DOI
- Merchant RE, Phillips TW, Udani J. Chlorella pyrenoidosa supplementation lowers serum methylmalonic acid in vegans and vegetarians suspected of vitamin B12 deficiency. Journal of Medicinal Food, 2015;18(12):1357-1362. DOI
- Siebert AK, Obeid R, Weder S, et al. An enriched toothpaste in vitamin B12 improves the vitamin status of vegans: a randomized placebo-controlled study of 12 weeks. American Journal of Clinical Nutrition, 2017;105(3):618-625. DOI
- Del Bo' C, Riso P, Gardana C, et al. Effect of two sublingual dosages of vitamin B12 on cobalamin status in vegans and vegetarians with marginal deficiency: a randomized controlled trial. Clinical Nutrition, 2019;38(2):575-583. DOI
- Eussen SJ, de Groot LC, Clarke R, et al. Oral cyanocobalamine supplementation in elderly persons deficient in vitamin B12: a dose-finding research trial. Archives of Internal Medicine, 2005;165(10):1167-1172. DOI
- Kwok T, Chook P, Qiao M, et al. Vitamin B12 supplementation improves arterial function in vegetarians with lowered vitamin B12 status. Journal of Nutrition, Health and Aging, 2012;16(6):569-573. DOI
- Koebnick C, Hoffmann I, Dagnelie PC, et al. Long-term ovo-lacto-vegetarian diet alters the vitamin B12 status of pregnant women. Journal of Nutrition, 2004;134(12):3319-3326. DOI
- Pawlak R, Vos P, Shahab-Ferdows S, et al. Vitamin B12 content of breast milk of vegan, vegetarian, and non-vegetarian women in the United States. American Journal of Clinical Nutrition, 2018;108(3):525-531. DOI
- Guez S, Chiarelli G, Menni F, et al. Severe vitamin B12 deficiency in a 5-month-old Italian infant exclusively breastfed, born to a mother receiving a multivitamin during pregnancy. BMC Pediatrics, 2012;12:85. DOI
- Mariani A, Chalies S, Jeziorski E, et al. Consequences of exclusive breastfeeding by a vegan mother: a case report. Archives de Pédiatrie, 2009;16(11):1461-1463. DOI
- Chalouhi C, Faesch S, Anthoine-Milhomme MC, et al. Neurological consequences of vitamin B12 deficiency and its treatment. Pediatric Emergency Care, 2008;24(8):538-541. DOI
- Jensen CF. Vitamin B12 levels in children and adolescents following a plant-based diet: a systematic review and meta-analysis. Nutrition Reviews, 2023;81(8):951-966. DOI
- Koller A, Rohrmann S, Wakolbinger M, et al. Health aspects of vegan nutrition in children and adolescents: systematic review and meta-analyses. Critical Reviews in Food Science and Nutrition, 2024;64(33):13247-13258. DOI
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