B12 on a Plant Based Diet

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B12 On A Plant Based Diet

This is the first of a series of posts I am sharing on plant based nutrition. I have personally enjoyed a plant based diet for close to ten years. Some of which have been as a vegetarian, and some as vegan. I have experienced numerous deficiencies during my journey, partly due to malabsorption, though I believe a lack of education was at the heart of it all. Yes, you can be healthy and well on a conscious and compassionate diet – but it takes careful planning and awareness of what your own unique body needs.  

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What you need to know

B12 (cobalamin) is required for DNA synthesis and cell division, and is essential for maintaining the integrity of the protective sheath (myelin) surrounding nerve fibres. A deficiency can result in neurological manifestations.

B12 is produced by bacteria in the large intestines of animals. This is also true for us – however, since the absorption of B12 occurs further up the colon (the terminal ileum), we are unable to make use of our own B12 synthesis. It is simply excreted via a bowel movement [1, 2, 3]. 

B12 for the most part, is found in animal products such as meat, poultry, seafood and dairy. It is not readily available in plant based foods, which makes it a nutrient of concern for those on a plant-based diet, particularly since a deficiency can cause serious health problems [1].

There are a lot of myths surrounding plant based sources of B12. Spirulina and blue-green algae contain a B12 analogue that is not bioavailable to us. Nutritional yeast may provide adequate amounts, though often it has been fortified with a synthetic form. Chlorella may be a good source, but B12  content varies widely. One recent study has found nori to be a great source, however, the study was conducted on rats. Further studies are needed to validate whether it is a truly reliable source. To summarise – plant based sources are simply not reliable.

Strict vegetarians/vegans may not notice a deficiency for years after starting a plant based diet, as the body readily stores B12. It is a good idea to be proactive and take a blood test to discern your B12 status. The traditional serum B12 blood test is controversial as it isn’t a very sensitive test – it measures the total sum of both active and inactive forms of B12. Better markers for B12 status may be homocysteine, methylmelonic acid and holotranscobalamin.

Supplementation may be required to meet needs after a while, methylcobalamin being the most active form. Absorption of B12 depends on a healthy gut and adequate levels of hydrochloric acid.   

B12 RDI:

2.4 mcg/day for adult men and women. 

2.6 mcg/day during pregnancy.

2.8 mcg/day during lactation.

There is no set upper level of intake, with no evidence to suggest adverse effects associated with excess B12 intake from food or supplements in healthy individuals [4].


The term ‘vitamin B12’ actually refers to a group of compounds with a central cobalt atom (known as “corrinoids”). Of the five forms, cyanocobalamin is the synthetic form you may be familiar with, as it is formulated in supplements. Hydroxycobalamin, aquacobalamin, methylcobalamin (methyl-B12) and 5-deoxyadenosylcobalamin are all natural sources, methyl-B12 being a highly active form [5].

What does vitamin B12 do? 

  • B2, B5, B6, B12 and folate (B9) all have a role in blood cell production. B12 is needed to produce red blood cells in the bone marrow, and activates folacin coenzymes to further enhance production. Healthy red blood cells are important in order to deliver oxygen and nutrients to the body’s tissues
  • Required for the metabolism of carbohydrates, lipids and proteins
  • Required for cellular energy
  • Required for DNA synthesis
  • It plays a role in reducing homocysteine – a marker for cardiovascular disease. High homocysteine with low B12 and folate is commonly seen in those with depression
  • B12 maintains the sheath surrounding and protecting nerve fibres
  • It has direct antioxidant action

[5, 6, 7].

B12 Deficiency

Major signs of deficiency include megaloblastic anaemia and neurological manifestations [14]. Deficiency can cause an erosion of the protective sheath around nerve fibres in the periphery, spinal cord, optic and cranial nerves, and brain.

The neurological symptoms experienced may include;

  • Numbness and tingling of the hands and feet
  • Decreased sensation
  • Dementia
  • Depression
  • Poor memory
  • Mood swings
  • Psychosis

Damage caused may be irreversible if not detected early [1, 8].

Other signs and symptoms include;

  • Fatigue
  • Weakness
  • Loss of appetite
  • Loss of bladder or bowel control
  • Sore mouth and tongue

[8, 9].

What causes a B12 deficiency?

  • Inadequate dietary intake (common in vegetarian/vegans)
  • Lack of intrinsic factor
  • Low stomach acid
  • Malabsorption conditions (inflammatory bowel, coeliac)
  • Some medications
  • Older age (the elderly are more at risk)
  • Increased requirements (pregnancy, lactation)
  • Alcoholism
  • Gut infections or parasites
  • Surgery to remove part of the stomach or bowel

In actuality, of the known cases of B12 deficiency in the wider population, 95% are due to inadequate absorption or impaired utilisation. Inadequate dietary intake, increased requirements (such as pregnancy and lactation), and increased excretion due to alcoholism make up the remainder. However, in regards to vegetarian and vegan populations, inadequate dietary intake does account for the major cause [1].

Gut health matters: Digestion and absorption of B12

The digestion and absorption of B12 is a little bit like ‘pass the parcel’ – with numerous protein transporters taking turns at escorting it along the digestive tract.

When vitamin B12 is consumed from dietary sources, it is bound to protein and must be released in order to be absorbed. Once it reaches the stomach, gastric acid – also known as hydrochloric acid (HCl), with the help of enzymes, detaches the B12 from the protein. From here, another protein (R-factor) attaches to the B12 and transports it to the small intestine [1].

Meanwhile, intrinsic factor (a glycoprotein) is being produced by parietal cells within glands located in the fundus and body of the stomach [10]. Its secretion is stimulated by pathways that also stimulate gastric acid secretion [11]. It travels from the stomach to the small intestine and forms a complex with B12 after the R-factor has delivered it and been enzymatically degraded. The new B12-intrinsic factor complex protects the B12 from the environment in the gut, and transports it to the terminal ileum (the very end section of the small intestine) where it is finally absorbed by intestinal cells with the help of yet another protein transporter [1, 8].

A B12 deficiency may be caused by a lack of production or function of intrinsic factor, leading to malabsorption. This is known as pernicious anaemia. Deficiency may also occur due to genetic defects resulting in malabsorption despite adequate, functioning intrinsic factor [12]. It is worth noting that medications that reduce gastric acidity (such as those taken for stomach ulcers) will consequently impact B12 absorption. Any resection (removal) of the ileum will decrease absorption, as will conditions such as irritable bowel syndrome, ulcerative colitis and Crohn’s disease. Finally, bacteria and intestinal parasites may compete for B12 [5].

Naturopathically speaking, it’s important to maintain stomach acid (hydrochloric acid – HCl), given its role in liberating the vitamin from food. Things that may adversely affect stomach acid are infections such as H. pylori, chronic overeating, chronic stress, excess intake of processed foods and carbohydrates, caffeine and alcohol (sorry!) [10]. A microbial imbalance in the small intestine, also known as intestinal dysbiosis or Small Intestinal Bacterial Overgrowth (SIBO), often occurring after antibiotics, may also contribute to a decrease in HCl [13].

A whole foods diet that includes plenty of bitter foods is a great way to keep gastric acid stimulated. Anecdotal evidence suggests apple cider vinegar before a meal is also helpful, and, in some cases, a Naturopath or Herbalist may see it appropriate to prescribe digestive bitters such as gentian, dandelion and wormwood.

Vegetarian / Vegan Needs

Vegans have a greater risk of developing a B12 deficiency, relative to non-vegetarians [14]. However – it may take years to notice deficiency symptoms as the body can store B12 for a very long time.

Food sources

As mentioned, Vitamin B12 is synthesized by certain types of bacteria, and concentrated in the bodies of predators higher in the food chain [15]. Sources include;

  • Meat
  • Milk
  • Eggs
  • Fish
  • Shellfish

Of the above, the bioavailability (the amount of B12 that is absorbed into systemic circulation and hence available for use) of fish, lamb and chicken ranges from 42%-66%. Less than 9% of vitamin B12 from eggs is absorbed [14], and furthermore, up to 10% is lost in cooking [5]. 

Plant based sources

Generally speaking, B12 is not readily available on a plant based diet. However, there are a few foods in which it is found, in varying amounts. This is an incredibly grey area however, and while it is true that a few isolated studies have found good amounts of B12 in plant foods (such as nori), they need to be repeated on a larger scale, in humans, before anyone can safely recommend them as a truly reliable source without the need for supplementation.

Additionally, a common trap many fall in to, is thinking a food has appreciable amounts of B12, when in actual fact, the amount per serving of that food is just not significant.


Tempeh, fermented soy bean, was shown in one study to be a great source of B12, however, the amount of B12 per 100g can vary so widely that it is simply not a reliable source [14]. 

Nori ­– the research on B12 content in nori (purple laver) – the dried and toasted seaweed you make sushi with, is probably the most promising. Animal studies have shown it to be in a bioavailable form, with a 4g serving meeting the RDI for adults [14, 16]. Again, it is risky to bet all your B12 just on nori – there could well be huge variations in B12 content within regions, and human studies are needed to validate findings.

Chlorella, a microalgae that is often sold as a supplemental powder or tablets, contains biologically active B12. A recent study found that that B12 content however widely varied – from zero to several micrograms per 100g dry weight [15]. It would be a good idea to check the nutritional panel on chlorella products to see what it is you are really getting.

Shiitake mushrooms have been shown to contain high levels of B12 in a bioavailable form. About 50g of dried shiitake mushroom would meet the RDI for adults, however this just doesn’t seem practical on a day to day basis [15].

Nutritional yeast is another source of B12. I have not come across any studies yet that determine whether this is in the bioavailable or analogue form. Some brands fortify their nutritional yeast with B vitamins. I believe the Braggs brand however contains B12 due to a natural fermentation. 

In addition to the few plant based sources, many cereals, soy products and vegetarian ‘meats’ are fortified with B12. 

Myth busting

Spirulina and edible algae other than those mentioned do not provide active B12. They contain an analogue that is not bioavailable to humans. There is a blue-green algae (Aphanizomenon flos-aquae) on the market advertised as having one of the highest percentages of B12 on the planet – however, in actual fact, it contains only pseudovitamin B12 – which is biologically inactive in humans [14].

B12 myth busting: spirulina and blue-green algae are NOT sources of B12 for humans! Click To Tweet

B12 On A Plant Based Diet

Spirulina and blue-green algae are not sources of B12! They contain analogues that are biologically inactive.

Folate can ‘mask’ a B12 deficiency

A B12 or folate deficiency can result in megaloblastic anaemia – a term used to describe large, immature red blood cells that can’t divide, or carry oxygen efficiently. It is important to discern which nutrient is deficient, as giving folate to someone who is in fact B12 deficient will correct the anaemia but not the neurologic damage, which may become irreversible [9].  

This is how folate can ‘mask’ a B12 deficiency, and, as vegetarians/vegans typically have (or should have!) a diet rich in leafy greens (folate), it is a good idea to be proactive and get blood tests to discern B12 status.

Testing for B12

Typically, a blood test is taken to assess serum B12 status. However, there are some controversies around this. It is thought that this method is inaccurate as it does not discern whether the B12 in the blood is the active or biologically inactive form [17]. This means analogues in foods such as sea vegetables and green powders (spirulina, blue green algae, barley grass) could give a person a falsely high reading.

There are other blood tests that can be helpful in detecting both B12 and folate deficiencies. These include homocysteine and methylmelonic acid (MMA). In a B12 deficiency, Homocysteine and MMA will be elevated, while only homocysteine (not MMA) will be elevated with a folate deficiency [18]. Raised plasma homocysteine levels are associated with long-term cardiovascular risk, and risk of neurodegenerative diseases such as Alzheimer’s [19].

Holotranscobalamin II (TC2) is another way to assess B12. It is a protein that transports B12 in the blood, falling with a deficiency [1]. It is thought to be a far more sensitive test than the standard serum B12 blood test [20].


Vegetarians consuming dairy and eggs will still be receiving B12 in the diet, however vegans need to rely on supplement or conscious consumption of fortified foods, as natural plant based sources do not provide significant or reliable amounts [1]. The body can only absorb a little B12 at a time. Studies suggest small and frequent doses are advantageous [21].

This is part of a series on plant based nutrition. If you enjoyed the article and learnt something new, please feel free to share. Sign up to my newsletter below to get the series in your inbox as they come. My plan is to post these fortnightly.


In the series:

Iron on a Plant Based DietProtein on a Plant Based DietCalcium on a Plant Based DietZinc On A Plant Based Diet

  1. Zeuschner, C.L., Hokin, B.D., Marsh, K.A., Saunders, A.V., Reid, M.A., & Ramsay, M.R. (2012). Vitamin B12 and vegetarian diets. MJA Open, 1(2), 27-32. Doi: 10.5694/mjao11.11509
  2. Kau, A.L., Ahern, P.P., Griffin, N.W., Goodman, A.L., & Gordon, J.I. (2011). Human nutrition, the gut microbiome, and immune system: envisioning the future. Nature, 474(7351), 327-336. Doi: 10.1038/nature10213
  3. Allen, R.H., & Stabler, S.P. (2008). Identification and quantitation of cobalamin and cobalamin analogues in human feces 1’2’3. American Society for Clinical Nutrition, 87(5), 1324-1335. Retrieved from http://ajcn.nutrition.org/content/87/5/1324.long
  4. Nutrient Reference Values for Australia and New Zealand. (2014). Vitamin B12. Retrieved from https://www.nrv.gov.au/nutrients/vitamin-b12
  5. Braun, L, & Cohen, M. (2015). Herbs & natural supplements. An evidence-based guide (4th ed., Vol. 2). Sydney, Australia: Churchill Livingstone
  6. Harvard Medical School. (2009). Retrieved from: http://www.health.harvard.edu/staying-healthy/listing_of_vitamins
  7. Coppen, A., & Bolander-Gouaille, C. (2005). Treatment of depression: Time to consider folic acid and vitamin B12. Journal of Psychopharmacology, 19(1), 59-65
  8. Osiecki, H. (2014). The nutrient bible (9th). Australia: Bioconcepts
  9. Whitney, E., Rolfes, S., Crowe, T., Cameron-Smith, D., Walsh, A. (2014). Understanding nutrition. Australia and New Zealand edition (2nd ed.). Melbourne, Victoria: Cengage Learning
  10. Seier, T., & Vayali, T. (2015). The hype of hypochlorhydia: A brief review of gastric acid analysis. Naturopathic Doctor News & Review. Retrieved from http://ndnr.com/gastrointestinal/the-hype-of-hypochlorhydria-a-brief-review-of-gastric-acid-analysis/
  11. Festen, H.P. (1991). Intrinsic factor secretion and cobalamin absorption. Physiology and pathophysiology in the gastrointestinal tract. Scandinavian Journal of Gastroenterology, 188, 1-7.
  12. Fyfe, J.C., Madsen, M., Hojrup, P., Christiensen, E.I., Tanner, S.M., de la Chapelle, A., … & Moestrup, S.K. (2004). The functional cobalamin (vitamin B12)–intrinsic factor receptor is a novel complex of cubilin and amnionless. Blood, 103, 1573-1579. Doi: 10.1182/blood-2003-08-2852
  13. James, M. (2013). Bacterial overgrowth of the small intestine breath test. In J.E. Pizzorno & M.T. Murray (Eds). Textbook of Natural Medicine (4th pp. 108-113). St Louis, MO: Elsevier Churchill Livingstone
  14. Watanabe, F. (2007). Vitamin B12 sources and bioavailability. Experimental Biology and Medicine, 232, 1266-1274. Doi: 10.3181/0703-MR-67
  15. Watanabe, F., Yabuta, Y., Bito, T., & Teng, F. (2014). Vitamin B12-Containing plant food sources for vegetarians. Nutrients, 6(5), 1861-1873. Doi: 10.3390/nu6051861
  16. Takenaka, S., Sugiyama, S., Ebara, S., Miyamoto, E., Abe, K., Tamura, Y., … & Nakano, Y. (2001). Feeding dried purple laver (nori) to vitamin B12-deficient rats significantly improves vitamin B12 status. British Journal of Nutrition, 20(5), 769-78. Doi: 10.1016/j.cmet.2014.10.002
  17. Biolab Medical Unit. (2012). Vitamin B12 – “active” B12 and plasma MMA. Retrieved from http://www.biolab.co.uk/docs/vitaminB12.pdf
  18. American Association for Clinical Chemistry. (2001-2016). Vitamin B12 and folate. Retrieved from https://labtestsonline.org/understanding/analytes/vitamin-b12/tab/test/
  19. BpacNZ. (2014). The New Zealand laboratory schedule and test guidelines: Biochemistry tests. Retrieved from http://www.bpac.org.nz/BT/2014/February/biochemistry.aspx
  20. Nexo, E., & Hoffman-Lucke, E. (2011). Holotranscobalamin, a marker of vitamin B-12 status: Analytical aspects and clinical utility1,2,3,4,5. The American Journal of Clinical Nutrition, 94(1), 359S-365S. Doi: 10.3945/ajcn.111.013458
  21. Herbert, V. (1987). Recommended dietary intakes (RDI) of vitamin B-12 in humans1-3. The American Journal of Clinical Nutrition, 45(4), 671-678.


Hi I’m Lauren, practising Naturopath, Medical Herbalist, Nutritionist, and essential oils educator in Auckland, New Zealand. I’m incredibly passionate about food as medicine, and helping people connect with the healing power of Nature. I’ve been sharing my recipes and health articles here since 2012.

BNatMed, AdDip NutMed, BCS, Certified FitGenes Practitioner.