Wondering how to get enough B12 on a vegan diet? Looking for tips on the best B12 supplements? I’ve got you covered in this science-based guide to vitamin B12.
“Vegans can get vitamin B12 through natural bacteria around their mouths.” “It’s a myth that vegans need to take vitamin B12 supplements.” “You can get enough B12 from the soil on your vegetables if you don’t wash them.” These are just three common myths floating around the plant-based community surrounding vitamin B12 intake for vegan diets. In fact, some popular vegan websites and publications hold the philosophy that vegans can meet all of their essential nutrient needs without the use of any supplements.
To be sure, this viewpoint is certainly not prevalent among all plant-based experts and websites. Most respected sources place great emphasis on supplementing the vegan diet with adequate B12 sources. The Vegetarian Resource Group (VRG) suggests that vegans need to have reliable sources of vitamin B12 in their diets. (1) The Vegetarian Nutrition Dietetic Practice Group (VNDPG) of the Academy of Nutrition and Dietetics says that all vegetarians (including vegans) should include a reliable B12 source in their diets, such as fortified foods or supplements. (2) And The Vegan Society goes so far as to state, “What every vegan should know about B12: the only reliable sources of B12 are foods fortified with B12 and supplements.” (3)
It’s extremely important for everyone following plant-based diets to understand the significance and intricacies of adequate vitamin B12 intake, because deficiency of this essential micronutrient is serious business.
What is Vitamin B12 and What Does it Do?
Vitamin B12 is a water-soluble vitamin, which contains the mineral cobalt and exists in several forms. Compounds with vitamin B12 activity are called cobalamins. Methylcobalamin and adenosylcobalamin are two forms that are active in human metabolism. The other active forms are hydroxycobalamin and cyanocobalamin, which must be metabolized into the two active forms to be used in human cells. B12 analogues—inactive forms—may be found in algae and some plant foods. (2, 4, 6)
Vitamin B12 is needed for proper red blood cell formation, neurological function, and DNA synthesis. The vitamin is a cofactor for methionine synthase, which catalyzes the conversion of homocysteine to methionine—required for the formation of S-adenosylmethionine, a universal methyl donor for almost 100 substrates, including DNA, RNA, hormones, proteins, and lipids. Methionine is also needed for the synthesis of myelin, a coating of the nerve pathways. Vitamin B12 is a cofactor for L-methylmalonyl-CoA mutase, which converts L-methylmalonyl-CoA to succinyl-CoA in the degradation of propionate, an essential biochemical reaction in fat and protein metabolism—succinyl-CoA is also required for hemoglobin synthesis. (2, 4)
B12 digestion and absorption requires the adequate synthesis of hydrochloric acid, proteases (enzymes that break down proteins and peptides), and intrinsic factor (a glycoprotein secreted in the stomach). The vitamin is released from dietary proteins by pepsin (the enzyme secreted in the stomach) and activated by hydrochloric acid. B12 binds with proteins secreted in the saliva, and in the small intestine pancreatic proteases digest the proteins, liberating the B12 to form a complex with intrinsic factor. Vitamin B12 can then be absorbed into the bloodstream via endocytosis in the distal ileum, or by passive diffusion in the absence of intrinsic factor. (2)
Pernicious anemia (an autoimmune disease) affects the gastric mucosa, leading to destruction of parietal cells and failure to produce intrinsic factor, resulting in vitamin B12 malabsorption and eventually deficiency. Older adults, who often suffer from decreased hydrochloric acid in the stomach, and individuals with gastrointestinal disorders may have lower absorption of B12. (2, 4)
Vitamin B12 deficiency may be characterized by megaloblastic anemia, fatigue, weakness, constipation, loss of appetite, soreness of the mouth or tongue, and weight loss; and neurological conditions, such as numbness and tingling of the hands and feet, difficulty with balance, depression, confusion, dementia, and poor memory. The neurological symptoms can occur without the presence of anemia, thus early detection is important to avoid irreversible damage. Deficiency is also commonly misdiagnosed, because symptoms can mimic other conditions. (2, 4)
Large intake of folic acid—common in vegan diets—can mask the damaging effects of B12 deficiency by correcting anemia, without addressing the neurological damage that occurs. High folic acid may even exacerbate anemia and cognitive symptoms. It’s not recommended to exceed 1000 mcg/day of folic acid in healthy adults. (4)
Sources of Vitamin B12
Vitamin B12 is only synthesized by microorganisms. Thus, it is not found in foods of plant origin. Natural animal food sources of vitamin B12 (which come from the animal’s intestines or from their diet) include fish, meat, poultry, eggs, milk, and milk products. Though some bacteria in the small intestines produce B12, it is not enough to maintain adequate status in humans. (2, 4)
According to vegan expert and co-author of Vegan for Life, Jack Norris, RD, there are no reliable sources of B12 in plants, contrary to many rumors about sources, such as tempeh, seaweeds, and organic produce. Plants have no B12 requirement, therefore they do not have any active mechanisms to make or store it. When you find B12 in plants, it is due to contamination, which is not a reliable source. Many seaweeds have B12 analogues, through their symbiotic relationship with cobalamin-producing bacteria, however the evidence is not clear that this form is active B12 in humans. And fermented foods, such as tempeh, are not fermented through B12-producing bacteria, thus they are not a source of B12. Rumors about bacteria on the surface of organic produce producing B12 have not been verified. “Chlorella may improve B12 status, but it’s by such a small amount that I wouldn’t rely on chlorella for B12,” adds Norris. Norris stresses that, unless a food obtained from multiple regions consistently improves B12 status, it should not be relied upon as a source of B12. (6)
B12 Status in Vegans
Naturally, vegetarians—especially vegans—are at risk for vitamin B12 deficiency. In fact there is a high prevalence of low-serum vitamin B12 among vegetarians, in particular vegans, where prevalence ranges at levels between 43 to 88% (5). Going back as far as 1955, studies have shown that vegans have experienced vitamin B12 deficiency. (7) In addition, B12 crosses the placenta during pregnancy and is present in breast milk—thus infants may suffer from B12 deficiency, which can lead to severe, permanent neurological damage. (4)
Norris says the story doesn’t end there. He reports that most vegans show adequate B12 levels to make clinical deficiency unlikely, but they may show restricted activity of B12-related enzymes, leading to elevated homocysteine levels, which has been linked to increased risk of heart disease and stroke. Thus, he warns that repeated observations of elevated homocysteine levels in vegans show that B12 intake needs to be addressed.
Best B12 Supplement Recommendations for Vegans
The RDA for B12 in adults is 2.4 micrograms per day (see sidebar), which assumes a 50% absorption rate from the amount ingested in foods. However, higher levels may be recommended to prevent potential deficiency symptoms in vegans. Intake of higher doses does not appear to be associated with detrimental health problems. (2)
The VNDPG recommends the following B12 guidance:
- All vegetarians, regardless of type, should periodically be screened for B12 deficiency, using either MMA (methylmalonic acid) or TCII (transcobalamin) assessment.
- All women considering pregnancy, and those already pregnant, should take 250 mcg/d* of a B12 supplement.
- All vegans should take 250 mcg/d* of a B12 supplement.
- All lacto-ovo vegetarians should consider taking 250 mcg/d* of B12 supplement a few times per week.
*This amount is about 100 times higher than the RDA due to the fact that only about 1% of ingested B12 from supplements is absorbed. (2)
Norris recommends vegan adults 18 – 65 years old should take one of the following regimens: two doses per day of 2 – 3.5 mcg per serving; one dose per day of 25 – 100 mcg per serving; or two doses per week of 1,000 mcg per serving. To read his full recommendations, visit here. (8)
| Recommended Dietary Allowances (RDAs) for Vitamin B12 | ||||
| Age | Male | Female | Pregnancy | Lactation |
| 0–6 months* | 0.4 mcg | 0.4 mcg | ||
| 7–12 months* | 0.5 mcg | 0.5 mcg | ||
| 1–3 years | 0.9 mcg | 0.9 mcg | ||
| 4–8 years | 1.2 mcg | 1.2 mcg | ||
| 9–13 years | 1.8 mcg | 1.8 mcg | ||
| 14+ years | 2.4 mcg | 2.4 mcg | 2.6 mcg | 2.8 mcg |
* Adequate Intake
Source: IOM. Food and Nutrition Board. Dietary References Intakes
In supplements, B12 is usually present as cyanocobalamin—a form the body readily converts into the active forms methylcobalamin and adenosylcobalamin. Other forms may be present in supplements, such as methylcobalamin and hydroxycobalamin. The vitamin B12 forms, cyanocobalamin and ocassionally hydroxocobalamin, can be administered by intramuscular injection to treat deficiency or cases of malabsorption. While absorption may not differ among forms of B12, the body’s ability to absorb the vitamin is largely limited by the capacity of intrinsic factor. (2, 4)
Many foods are fortified with B12, including breakfast cereals, meat analogues, soymilk, and nutritional yeast (see sidebar). They may be fortified from small amounts all the way up to 200% of the RDA. It’s important to read labels, as not all of these products are fortified, and fortification can change in products over time. (2) Norris reports that amounts listed on a nutrition label are based on 6 mcg per day. For example, a food that provides 25% of the Daily Value for B12 would provide 1.5 mcg. (8)
B12 Fortified Plant Foods
| Food | B12 (mcg) |
| Cereals, ready to eat, ½ c | <1.0 – 6.1 |
| Meat Anologues, 1 serving | 1.2 – 4.2 |
| Soymilk, 8 oz | <1.0 – 3.0 |
| Rice Drink, 8 oz | 1.5 |
| Protein Bar, fortified, 1 | 1.0 – 2.0 |
| Nutritional Yeast, Vegetarian Support Formula, 1 Tbsp | 4.0 |
*Amounts differ based on product formulation; check labels to determine how much B12 is in fortified food products.
Learn more about my top vegan supplements recommendations here. Check out my favorite B12 supplement here.
B12 Testing
The status of B12 is typically assessed through serum or plasma B12 levels. Values below 170 – 250 pg/ml for adults indicate a deficiency. However, this indicator may be influenced by other factors, such as low vitamin B6 or folate levels. Elevated methylmalonic acid (MMA) levels (greater or equal to .4 micromol/L) might be a more reliable indicator of B12 status, because it indicates metabolic changes more specific to B12 deficiency. (4)
Norris recommends MMA and serum vitamin B12 tests for vegan, adding, “You don’t need to get tested just because you’re vegan, rather you should make sure you follow the recommendations for intake.” Mangels also looks at MMA, as well as homocysteine levels to see if B12 status is adequate. “B12 works with other B vitamins in many biochemical cycles, so it’s important to understand the whole picture and look at a variety of nutrients,” says Mangels.
Clearing Up Confusions on B12
Norris says, “There is less confusion than during the 1990s and early 2000s, but there is still a lot. Many vegans don’t think vegans need to worry about B12, or they think that meat-eaters get B12 deficiency just as often as vegans do, while others think you have to supplement with methylcobalamin rather than the less expensive, more reliable cyanocobalamin.”
Mangels notes, “Some people think that they have enough vitamin B12 stored that they don’t need to worry about vitamin B12. There’s some confusion about reliable sources also. I would not count on sources like seaweed, spirulina, or soil.”
“I hear people that likely do need to supplement with B12 say that they’re ok because they eat foods that may include B12, but they can be unreliable sources, such as sea vegetables or nutritional yeast,” says Ginger Hultin, MS, RD, lifelong vegetarian, Chair of the VNDPG, and spokesperson for the Academy. “Each person should be treated as an individual, with their diet and health history in mind.”
For other resources on eating a healthy vegan diet, check out the following:
References:
- Mangels R. Nutrition Hotline. The Vegetarian Resource Group. 2015 (4). Accessed 2/2/18: https://www.vrg.org/journal/vj2015issue4/2015_issue4_nutrition_hotline.php
- Pawlak R. Vitamin B12 in Vegetarian Diets. Vegetarian Nutrition Dietetic Practice Group. Accessed on 2/2/18: https://vndpg.org/docs/rd-resources/B12-RD.pdf.
- Walsh S. B12 Recommendations. The Vegan Society. Accessed 2/2/18: https://www.vegansociety.com/resources/nutrition-and-health/nutrients/vitamin-b12/what-every-vegan-should-know-about-vitamin-b12
- Vitamin B12. National Institutes of Health, Office of Dietary Supplements. Accessed 2/2/18: https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/
- Melina V, Craig W, Levin S. Position of the Academy of Nutrition and Dietetics: Vegetarian Diets. J Acad Nutr Diet. 2016;116(12):1970-1980. Accessed 2/2/18: https://vegstudies.univie.ac.at/fileadmin/user_upload/inst_ethik_wiss_dialog/JAND_2015.05_Position_of_the_academy_of_nutrition_and_dietetics_vegetarian_diets..pdf
- Norris J. B12 in Plant Foods. VeganHealth.org. October, 2015. Accessed 2/5/18: https://www.veganhealth.org/b12/plant#intro
- Wokes F, Badenoch J, Sinclair HM. Human Dietary Deficiency of Vitamin B12. Am J Clin Nutr 1955; 3(5):375-82. Accessed 2/5/18: https://www.ncbi.nlm.nih.gov/pubmed/13258511.
- Norris, J. Vitamin B12 Recommendations. VeganHealth.org. Accessed 2/5/18: https://veganhealth.org/vitamin-b12/
- Mangels, R. Do Vegans have to take vitamin B12 supplements? Vegetarian Journal. 2015 (4). Accessed 2/5/18: https://www.vrg.org/journal/vj2015issue4/2015_issue4_nutrition_hotline.php
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