Yes. Natural food sources of B12 are limited to animal foods, and the US National Institutes of Health says fortified foods and supplements can substantially reduce a vegan’s risk of running short. The Vegan Society goes further: the only reliable vegan sources are fortified foods and B12 supplements, and nori, spirulina and tempeh don’t qualify.
Feeling fine tells you less than it seems to. The body stores about 1 to 5 mg of B12, roughly 1,000 to 2,000 times what a person takes in on a typical day, so deficiency symptoms can take several years to show up. The usual checks have a vegan-shaped blind spot as well. The Vegan Society points out that vegan folate intakes are generally good, especially with plenty of greens, and that high folate suppresses the anemia a blood count would otherwise catch. It also warns that algae contain B12 analogues, false B12, that can pass for the real thing on a blood test while interfering with how the body uses it. So a vegan who eats a lot of spinach and takes spirulina can get a normal blood count, a normal B12 reading and still have a B12 problem. The greens are covering for you, which is loyal of them and no help at all. Whether a vegan can do without supplements entirely is a bigger argument, and we take it on in veganism without supplements, fact or fiction.
Where can vegans get B12?
From two places that work, and a longer list of places that keep being suggested. NIH says B12 is not naturally present in plant foods, but that some plant foods are fortified with it, including many breakfast cereals and nutritional yeasts. The Vegan Society’s open letter on B12, written in 2001 by its trustee Stephen Walsh with members of the International Vegetarian Union science group, names fortified plant milks, some soy products, some breakfast cereals and supplements as the only reliable vegan sources. NIH’s word for nutritional yeasts is many, not all, so check the panel for B12 before you count a jar as your source. Our piece on why nutritional yeast turns up in so many vegan recipes covers what it is and what it does in a recipe.
The same letter goes through the alternatives one by one. Spirulina, nori, tempeh and barley grass have all been put forward as plant sources, and in its words “Such claims have not stood the test of time.” It lists human gut bacteria, spirulina, dried nori, barley grass and most other seaweeds as sources that direct studies of vegans have shown to be inadequate.
The strongest case on the other side is nori, and it is a serious one. A 2014 review in the journal Nutrients by Fumio Watanabe and colleagues concluded that dried purple laver, the seaweed sold as nori, is the most suitable B12 source presently available for vegetarians. It reports 77.6 µg of B12 per 100 g dry weight, says about 4 g a day supplies the US RDA of 2.4 µg, and found that toasting the sheets until they turned green did not change the B12 content. The same review is blunt about spirulina: supplements made from it often contain large amounts of pseudovitamin B12, which is biologically inactive in humans.
So the review and the Vegan Society agree on spirulina and disagree on nori. The Vegan Society’s answer is that finding B12 in a food is not enough, because true B12 is hard to tell apart from analogues, and analogues present in similar amounts can cancel it out. Its one test for a B12 source is whether it consistently prevents and corrects deficiency. The review’s case rests largely on the B12 measured in the seaweed. Our line sits with the Vegan Society. Eat nori because you like it, and don’t count it as your B12. The review’s own breakfast sheets weigh about 0.3 g each, which puts 4 g at around 13 of them a day (our arithmetic), every day, for the rest of your life.
How much B12 do vegans need?
NIH sets the RDA for adults at 2.4 mcg a day, rising to 2.6 mcg in pregnancy and 2.8 mcg while breastfeeding. The Daily Value on US food and supplement labels is the same 2.4 mcg, so on a fortified carton, 100% DV per serving means one adult RDA.
The Vegan Society asks for more than that and gives three ways to get it. Eat fortified foods two or three times a day for at least 3 mcg, take a daily supplement of at least 10 mcg, or take a weekly supplement of at least 2,000 mcg. On a label, 3 mcg a day is 125% DV (our arithmetic). The letter’s own example is a plant milk with 1 mcg per serving, drunk three times a day.
The weekly figure looks absurd until you see how absorption works. NIH puts absorption at about 50% for doses under 1 to 2 mcg, then only about 2% at 500 mcg and 1.3% at 1,000 mcg. The Vegan Society’s figure for doses of 1,000 mcg and above is lower still, about 0.5%, and that is why its weekly dose is so large: most of a big tablet never gets in. The letter also says to chew a tablet or let it dissolve in the mouth, and to stay under 5,000 mcg a week, while noting there is no evidence of toxicity from higher amounts. NIH adds that no evidence shows absorption differs by the form of B12 in a supplement, so for absorption at least, the dose on the label matters more than the form named on it.
Who should be stricter about it?
Anyone pregnant or breastfeeding, and anyone raising a vegan child, first. NIH warns that exclusively breastfed infants of women who eat no animal products may have very limited B12 reserves and can become deficient very early in life, sometimes while the mother’s own deficiency is mild enough to go unnoticed. The Vegan Society names the same group, breastfed infants of vegan mothers with a low intake, as one of two at particular risk, alongside long-term vegans who avoid common fortified foods, such as raw food and macrobiotic vegans. If either describes you, set the dose with a doctor or a registered dietitian rather than from this page.
Age matters too. The Vegan Society quotes the Institute of Medicine’s advice, written for the US intake recommendations, that because 10 to 30 percent of older people may not absorb B12 from food, people over 50 should get most of theirs from fortified foods or a supplement, and then adds that vegans should take that advice about 50 years younger. NIH also lists long-term use of metformin or proton pump inhibitors among the causes of deficiency. If you take either, ask your doctor about your B12.
How do you know if your B12 is low?
Not from the blood count, and not reliably from the standard B12 test, at least according to the Vegan Society, which calls a blood B12 measurement a very unreliable test for vegans, particularly vegans using any form of algae. NIH notes that serum B12 is the test usually done, with values under 200 or 250 pg/mL generally treated as low.
The better marker is methylmalonic acid, or MMA. NIH calls it the most sensitive marker of B12 status, with the caveat that MMA also rises with poor kidney function and tends to be higher in older adults. The Vegan Society calls MMA the most specific test, and treats a blood level under 370 nmol/L as enough B12. Homocysteine is the other option, which the Vegan Society prefers to a plain B12 reading, though NIH says it is less specific because low folate and declining kidney function also push it up. If you want to know where you stand, ask for MMA by name.
The part we are least sure about is the weekly tablet. At the Vegan Society’s 0.5%, a 2,000 mcg dose comes to about 10 mcg absorbed, or roughly 1.4 mcg a day (our arithmetic). NIH gives no figure for 2,000 mcg, but at its 1.3% for 1,000 mcg the same tablet would come to nearer 3.7 mcg a day (our arithmetic). The letter says you need to absorb about 1.5 mcg a day, so on its own lower figure its weekly option lands just short of its own target. We would want a newer measurement at 2,000 mcg before calling the weekly tablet settled. Which form of B12 to buy is the next question, and we take it up in our roundup of vegan B12 supplements, form and dose included.
Sources
- NIH Office of Dietary Supplements, Vitamin B12 fact sheet for health professionals (RDAs, vegan risk, absorption by dose, forms, body stores, MMA)
- The Vegan Society, What every vegan should know about vitamin B12 (open letter, October 2001: reliable sources, intake patterns, testing, at-risk groups)
- Watanabe F. et al., Vitamin B12-containing plant food sources for vegetarians, Nutrients 2014;6(5):1861-1873
- FDA, Daily Value on the Nutrition and Supplement Facts labels (vitamin B12 DV 2.4 mcg)
