Does needing B12 make a vegan diet unnatural?

The objection

“Every other animal gets what it needs from the food it evolved to eat, and people got their B12 from meat, fish, eggs and milk long before anyone made a pill. A diet that is only safe with a factory-made supplement is incomplete by definition, and calling it healthy is spin.”

The answer

The premise holds as far as it goes. Plants don’t supply vitamin B12, and the British Dietetic Association (BDA) says in its 2021 fact sheet that for vegans the only reliable sources are fortified foods and supplements, warning that too little can cause fatigue, anaemia and nerve damage [1]. The CDC (2026) warns that a baby fed only breast milk by a mother who eats no animal products is more likely to become deficient soon after birth, that untreated deficiency in infants can cause permanent brain damage, and that vegan mothers who breastfeed should ask a health professional about a B12 supplement [2]. Every vegan needs a dependable source of B12, at every age. On average their B12 status still lags: a 2024 meta-analysis of 17 studies (Niklewicz et al.) found significantly lower serum B12 and higher homocysteine, a functional marker of deficiency, in vegan adults than in omnivores, though two other markers did not differ significantly. Vegans who took B12 supplements had significantly better levels on every marker than those who did not [7].

Vegans have more to plan than B12, too. In the UK and Ireland milk and dairy are the main sources of iodine and iodised salt is hard to find [3][4], so the BDA points vegans to iodine-fortified plant milks, checking the label, or a suitable iodine supplement [1][3]. It warns against kelp and seaweed supplements, whose iodine content can stray far from the label, gives about 600 micrograms a day as a rough upper limit for adults, and advises anyone with thyroid disease or a long-term low intake to check with a GP before taking extra iodine [3]. The NHS lists vitamin D, B12, iodine, selenium and calcium as nutrients that are harder to get on a vegan diet and may need to come from fortified foods or supplements [5]. Where the objection goes wrong is in assuming that the meat-eater’s diet arrives without help.

Where does the B12 in meat and milk come from?

The B12 in meat and milk was made by microbes, like all B12. Only a few kinds of bacteria and archaea can make the vitamin, which is why it is produced industrially by fermentation (Fang et al., 2017) [6] and why plants are not a reliable source of it [1]. Cattle and sheep can’t make it either. Microbes in the rumen make it from cobalt, and a 2025 review of dairy cattle nutrition notes that the cobalt in forage and many feeds is typically too low to meet the needs of the cow and its microbes, which makes supplements necessary; a cow short of cobalt eats less, grows poorly and gives less milk (Siregar et al., 2025) [8]. The finished vitamin goes into feed as well. The European Food Safety Authority (EFSA) noted in 2023 that B12 has been used in animal nutrition worldwide for decades, typically at 3 to 150 micrograms per kilo of feed depending on the species, and that the EU authorises it for every animal species with no maximum level [9]. That feed B12 is made, like the B12 in a vegan’s tablet, by microbial fermentation [6][9], and the tablet leaves the animal out.

Milk tells the same story with iodine. In Irish national food surveys of 516 schoolgirls aged 5 to 18 (2017 to 2020), milk supplied over half their iodine, and Kane et al. (2025) explain that milk is a good source partly because in some regions it is standard practice for farmers to use iodine-based disinfectants on the animals’ teats and to give livestock trace-mineral concentrates or mineral licks [4]. Even so, 40% of the girls took in less iodine than the estimated average requirement, and their median urinary iodine pointed to mild deficiency [4].

Do meat-eaters rely on supplements and fortified food too?

Meat-eaters are told to use supplements and fortified food too, under official advice that applies whatever you eat. An estimated 10 to 30% of people over 50 have atrophic gastritis, with low stomach acid, and so may absorb the B12 in food poorly, because the vitamin in food is bound to proteins and needs stomach acid to be released. The US Institute of Medicine therefore advised in 1998 that everyone over 50 should get most of their B12 from fortified foods or a supplement, whose B12 they absorb normally [10], and Health Canada’s current reference tables (page updated in 2025) repeat that advice [11]. The reason in their case is absorption rather than diet, and a vegan’s need starts earlier because plants don’t supply the vitamin [1], but the remedy is the one official advice already gives everyone over 50. The NHS advises adults and children over 4 in the UK to consider a daily vitamin D supplement in autumn and winter, because it is difficult to get enough from food alone, and warns adults not to take more than 100 micrograms a day [12]. Anyone trying for a baby is advised to take folic acid, ideally from three months before conception until 12 weeks of pregnancy, again because it is hard to get enough from food alone, and some, including women with diabetes or who take medicine for epilepsy or HIV, need a higher 5 mg dose that a GP can prescribe [13]. High doses of folic acid carry a catch for anyone short of B12, because they can clear up the anaemia of B12 deficiency, at least for a time, while nerve damage continues or possibly worsens (Miller et al., 2024) [19]. That review calls the evidence that excess folic acid makes the deficiency itself worse mostly correlational or from uncontrolled observations, but still urges clinicians to check B12 status more closely in groups at risk, vegans and vegetarians among them [19].

Advice	Who	Amount
Vitamin D in autumn and winter (NHS)	Adults and children over 4 (the NHS has separate advice for babies, children aged 1 to 4 and people who get little sun)	10 µg a day [12]
Folic acid (NHS)	Anyone trying for a baby, to 12 weeks of pregnancy	400 µg a day [13]
B12 mainly from fortified food or a supplement (US, Canada)	Everyone over 50	Most of the 2.4 µg a day [10][11]
B12 (the Vegan Society, a vegan advocacy group, as quoted by the BDA)	Vegans	Fortified food at least twice a day aiming for 3 µg a day, or a supplement of at least 10 µg a day or 2,000 µg a week [1]

The NHS says vegans who are pregnant or breastfeeding need to make sure they get enough vitamins and minerals for their child to develop healthily, and that a baby or child brought up vegan needs a wide variety of foods for growth [5], so parents and parents-to-be should ask a GP, midwife, health visitor or dietitian which supplements to take or give, and in what amounts.

Staple foods carry added nutrients for everyone as well. UK non-wholemeal wheat flour is fortified by law with calcium, iron, niacin and thiamin, and from December 2026 it must carry folic acid too, a change expected to cut neural tube defect rates in the UK by around 20%, according to the Food Standards Agency [14]. More than 60 countries, including Australia, Canada and the US, add folic acid to wheat flour, by law or voluntarily [14]. People taking certain medicines may need to watch their folic acid intake or avoid folic acid supplements, and the agency advises them to seek advice from a healthcare professional [14].

Is ‘natural’ a good test of a healthy diet?

Whether a diet is natural is a poor test of whether it is healthy, because what matters is what the diet does to the people who eat it. Folic acid, the synthetic form of folate [14], is the only type of folate shown in studies to help prevent neural tube defects such as spina bifida, according to the CDC (2026) [15]. A Cochrane review of five randomised trials (De-Regil et al., 2015) found that taking it around conception, alone or with other vitamins and minerals, cut these defects by more than two-thirds (risk ratio 0.31, 95% CI 0.17 to 0.58, 6,708 births), evidence it rated as high quality [16]. The benefit was clearest in women who had already had an affected pregnancy (risk ratio 0.34, 0.18 to 0.64), while the one trial of first-time prevention, with 4,862 births, recorded no cases among women given folic acid, though its result (risk ratio 0.07, 0.00 to 1.32) could not rule out no effect [16]. The Medical Research Council’s 1991 trial randomised 1,817 women with a previous affected pregnancy to folic acid, other vitamins, both or neither, and recorded 27 neural tube defects among 1,195 completed pregnancies: 6 in the two groups given folic acid and 21 in the two without it, a relative risk of 0.28 (95% CI 0.12 to 0.71) [17].

Adding nutrients to staple foods shows the same pattern across whole populations. A 2019 meta-analysis of large-scale fortification programmes in low- and middle-income countries found 41% lower odds of neural tube defects after folic acid went into flour (odds ratio 0.59, 95% CI 0.49 to 0.70, eight studies), 74% lower odds of goitre in school-age children after salt iodisation (0.26, 0.16 to 0.43, eight studies) and 34% less anaemia after iron fortification (risk ratio 0.66, 0.59 to 0.74, 11 studies) (Keats et al., 2019) [18]. Most of its studies compared surveys taken before and after a programme began, a design the authors say limits causal conclusions, and they graded the evidence for each of these three outcomes as moderate quality [18]. The review was funded by the Global Alliance for Improved Nutrition, which has a specific interest in fortification, though the authors say their co-authors from the alliance took no part in searching for, selecting or analysing the studies [18]. A Cochrane review published the same year found only one study among those it included, a non-randomised one of 8,037 births, that measured neural tube defects after flour fortification: wheat flour fortified with folic acid and other micronutrients was linked to fewer defects (risk ratio 0.32, 95% CI 0.21 to 0.48), but the review rated that evidence low certainty and concluded only that fortification may reduce the risk (Centeno Tablante et al., 2019) [20].

Natural foods are not automatically safe either: the NHS tells pregnant women to avoid liver, because too much vitamin A can harm the baby’s development [13]. Planning matters because the risks are real: in the EPIC-Oxford cohort (2020), vegans had 2.31 times the meat-eaters’ rate of hip fracture after allowing for socio-economic factors, lifestyle and body mass index, equivalent to 14.9 more cases for every 1,000 people over 10 years, and 1.43 times their rate of fractures overall (Tong et al., 2020) [21]. As for what a planned vegan diet does, the BDA says carefully planned plant-based diets can support healthy living at every age and life stage [1], and the NHS says that with good planning a vegan diet can provide all the nutrients the body needs [5].