Vitamin B-12, Vegans & Cancer

Given that many mainstream vegans develop B12 deficiency when not supplementing their diets with B12, intestinal bacteria cannot be relied upon to prevent B12 deficiency in vegans. However, holistic vegans will know how to fix this  problem.

Bacteria in the Large Intestine

It has long been assumed that B12 is produced by bacteria in the large intestine (aka the colon), but since B12 is produced below the ileum (where B12 is absorbed),it is not available for absorption. This theory is reinforced by the fact that many species of totally or primarily vegetarian animals eat their feces. Eating feces allows them to obtain B12 on their diets of plant foods.

The best evidence I have found for this theory is reported by Herbert (1). He reports a study in the 1950s in England where vegan volunteers with B12 deficiency (as shown by megaloblastic anemia) were fed B12 extractions made from their own stools and it cured their deficiency. He said it proves that the colon bacteria of vegans produce enough B12 to cure a deficiency, but that the B12 produced by the bacteria in the colon is excreted rather than absorbed. This appears to be convincing evidence.

However, the study Herbert cites as the source, “Callender ST, Spray GH. Latent pernicious anemia. Br J Haematol. 1962;8:230-40,” does not mention this experiment.

There is another study by Callender and Spray that sounds like it could be the one Herbert is describing, “Preparation of hematopoietically active extracts from faeces. Lancet 1951(June 30):1391-2.” This study was not performed on vegans, but rather on people with pernicious anemia who cannot properly absorb B12. The B12 was isolated from the stool samples and given to the subjects intravenously. Because these people were ingesting B12, the B12 in their stool could have been from the B12 they were eating.

On the other hand, according to Lactobacillus lactis Dorner and Lactobacillus leichmannii assays, there were substantial amounts of B12 analogue found in the feces(e.g., 5 µg per 10 ml (2 teaspoons)). This seems like too much to have been provided by only the diet and enterohepatic circulation. Apparently, some of this B12 analogue was active, and there was enough to counteract any inactive B12 analogue in their stools. Thus, this study provides good evidence that there is active B12 produced by bacteria in the colon of at least some humans.

A variable to consider is that there are over 400-500 species of bacteria in the average human’s colon and these bacteria have not all been delineated. It is plausible that some humans have B12-producing bacteria in significant amounts while other humans do not. Some bacteria in the digestive tract absorb B12 for their own use, further complicating this situation.

Allen and Stabler found that more than 98% of B12 analogue in the human stool is inactive (2). This was in people who had a consistent intake of vitamin B12. They determined that 81% of nonabsorbed, ingested B12 was destroyed or degraded into inactive analogue. This may or may not be the case in people with much lower, or no, vitamin B12 intakes.

Bacteria in the Small Intestine

B12 deficiency has been found with relatively high frequency among vegetarian Indian immigrants in England, while at one time it was thought to be uncommon among native Indians with identical dietary patterns, possibly because healthy Indian subjects have a more extensive amount of bacteria in their small intestine than people in the West (3).

Albert et al. (3) (1980) measured B12 production of bacteria in the small intestines of people in India using a Euglena gracilis Z assay. Results were confirmed by an Ochromonas malhamensis assay, which is thought to be specific for active B12. They determined that some active B12 was produced by members of the bacteria genera Klebsiella and Pseudomonas. Further confirmation using chromatography and bioautography showed a molecule with similar properties to cyanocobalamin. Albert et al. speculated that when Indians migrate to the West, their digestive tracts become like those characteristic of people in Western countries: with little or no bacteria in their upper small intestines. An article in Nutrition Reviews (5) (1980) suggested some alternative causes of Indian immigrants to Britain having more B12 deficiency than Indian natives:

  • In India, water is contaminated with various bacteria, including those from human and animal feces.
  • The practice of defecating in open fields and lack of proper sewage.
  • The mode of toilet hygiene where water is used instead of toilet paper.

It should also be noted that B12 deficiency is fairly common in India (see the table below), especially in lower income, lacto-ovo vegetarians (6).

Iranian Villagers

Halstead et al. (8) reported that some Iranian villagers with very little animal product intake (dairy once a week, meat once a month) had normal B12 levels. None had megaloblastic anemia. Their average B12 level was 411 pg/ml which was quite high considering their diet.The authors speculated this could be because their diets, which were very low in protein,allowed for B12-producing bacteria to ascend into the ileum where the B12 could be absorbed.They also speculated that because they lived among their farm animals and their living areas were littered with feces, they picked up enough B12 through contamination.

Halstead et al.’s 1960 report was in contrast to Wokes et al.’s 1955 report (9) in which numerous British vegans were found to have neurological symptoms of B12 deficiency.

Holistic Vegans

Holistic vegans can be successful in avoiding Vit B 12 problems by eating in a more holistic way, eating some organic soil from their garden, using lots of bacteria rich compost and manure in garden helps also as does many mountain spring water sources specific foods that most maisntream vegans don’t eat, in particular mushrooms seaweed and fermented foods

A survey of naturally occurring and high Vitamin B12-containing plant-derived food sources showed that nori, which is formed into a sheet and dried, is the most suitable Vitamin B12 source for vegetarians presently available. Consumption of approximately 4 g of dried purple laver (Vitamin B12 content: 77.6 μg /100 g dry weight) supplies the RDA of 2.4 μg/day. In Japan, several sheets of nori (9 × 3 cm2; approximately 0.3 g each) are often served for breakfast. A large amount of nori can be consumed as certain forms of sushi (vinegared rice rolled in nori). In particular, hand-rolled sushi made by wrapping rice and fillings with nori is easy to prepare and facilitates the consumption of a large amount of nori. When dried purple laver was treated by toasting until the laver’s color changed from purple to green, the toasting treatment did not affect the Vitamin B12 contents. [10].

Dried purple lavers could also be a suitable food item for integration in Italian, French, and other forms of western cuisine. Dried purple laver is also a rich source of iron and n-3 polyunsaturated fatty acids. Dried purple laver is a natural plant product; therefore, it is suitable for most vegetarian groups.

Among edible mushrooms, relatively high levels of Vitamin B12 were detected in the commercially available shiitake mushroom fruiting bodies, but the Vitamin B12 content significantly varies (1.3–12.7 μg/100 g dry weight), which is significantly lower than that found in dried purple laver. However, the dried shiitake mushroom fruiting bodies (per 100 g) contain 18.9 mg of Vitamin D2 (ergocalciferol) and 2.0 mg of iron [11], which are also nutrients that vegetarian diets tend to lack. Thus, the use of these plant-based food sources can significantly improve the nutrient imbalance in vegetarian diets to reduce the incidence of Vitamin B12 deficiency in vegetarians.

For fermented foods


The bodies requirement for vitamin B12 is actually very low. Non-animal sources include Red Star Vegetarian Support Formula or T-6635+ nutritional yeast (a little less than 1 Tablespoon supplies the adult RDA), and vitamin B12 fortified soymilk. It is especially important for pregnant and lactating women, infants, and children to have reliable sources of vitamin B12 in their diets.

The Need for Vitamin B12

Vitamin B12 is needed for cell division and blood formation. Plant foods do not contain vitamin B12 except when they are contaminated by microorganisms. Thus, vegans need to look to other sources to get vitamin B12 in their diet. Although the minimum requirement for vitamin B12 is quite small, 1/1,000,000 of a gram (1 microgram) a day for adults [1], a vitamin B12 deficiency is a very serious problem leading ultimately to irreversible nerve damage. Prudent vegans will include sources of vitamin B12 in their diets. However, vitamin B12 deficiency is actually quite rare even among long-term vegans.

Normally, vitamin B12 is secreted into the small intestine along with bile and other secretions and is reabsorbed, but this does not add to the body’s vitamin B12 stores. Since small amounts of vitamin B12 are not reabsorbed, it is possible that eventually vitamin B12 stores will be used up. However, we may be quite efficient at re-using vitamin B12 so that deficiency is rare.

Bacteria in the human intestinal tract do make vitamin B12. The majority of these bacteria are found in the large intestine. Vitamin B12 does not appear to be absorbed from the large intestine [1].

Possible Vitamin B12 Sources

Some bacteria in the small intestine do produce vitamin B12 [2]. The amount of vitamin B12 which is produced does not appear adequate to prevent vitamin B12 deficiency [3].

Although some vegans may get vitamin B12 from inadequate hand washing, this is not a reliable vitamin B12 source. Vegans who previously ate animal-based foods may have vitamin B12 stores that will not be depleted for 20 to 30 years [1] or more. However, long-term vegans, infants, children, and pregnant and lactating women (due to increased needs) should be especially careful to get enough vitamin B12.

Reliable Vegan Sources of Vitamin B12

A number of reliable vegan food sources for vitamin B12 are known. One brand of nutritional yeast, Red Star T-6635+, has been tested and shown to contain active vitamin B12. This brand of yeast is often labeled as Vegetarian Support Formula with or without T-6635+ in parentheses following this new name. It is a reliable source of vitamin B12. Nutritional yeast, Saccharomyces cerevisiae, is a food yeast, grown on a molasses solution, which comes as yellow flakes or powder. It has a cheesy taste. Nutritional yeast is different from brewer’s yeast or torula yeast. It can often be used by those sensitive to other yeasts.

The RDA (which includes a safety factor) for adults for vitamin B12 is 2.4 micrograms daily [4]. 2.4 micrograms of vitamin B12 are provided by a little less than 1 Tablespoon of Vegetarian Support Formula (Red Star T-6635+) nutritional yeast. A number of the recipes in this book contain nutritional yeast.

1. Herbert V. Vitamin B12: Plant sources, requirements, and assay. Am J Clin Nutr1988; 48: 852-858.

2. Albert MJ, Mathan VI, Baker SJ. Vitamin B12 synthesis by human small intestinal bacteria. Nature1980; 283: 781-782.

3. Callender ST, Spray GH. Latent pernicious anemia. Br J Haematol1962; 8: 230-240.

4. Institute of Medicine, Food and Nutrition Board: Dietary Reference Intakes for Thiamin, Riboflavin, Niacin, Vitamin B-6, Folate, Vitamin B-12, Pantothenic Acid, Biotin, and Choline. Washington, DC: National Academy Press, 1998.


It is possible that some vegans can ward of overt vitamin B12 deficiency, and even mild B12 deficiency, through B12 production by bacteria in the small intestine. However, this is an unusual condition, especially among mainstream vegans in Western countries, and should not be relied upon. On the other hand, by adopting a holistic lifestyle, all should be good. But to be on the safe side, one should get tested for B 12 and also to see if homocystein is not high.

Ch. J.


1. Herbert V. Vitamin B-12: plant sources, requirements, and assay. Am J Clin Nutr 1988;48:852-8.

2. Allen RH, Stabler SP. Identification and quantitation of cobalamin and cobalamin analogues in human feces. Am J Clin Nutr. 2008 May;87(5):1324-35.

3. Albert MJ, Mathan VI, Baker SJ. Vitamin B12 synthesis by human small intestinal bacteria. Nature. 1980;283(Feb 21):781-2.

4. Refsum H, Yajnik CS, Gadkari M, Schneede J, Vollset SE, Orning L, Guttormsen AB, Joglekar A, Sayyad MG, Ulvik A, Ueland PM. Hyperhomocysteinemia and elevated methylmalonic acid indicate a high prevalence of cobalamin deficiency in Asian Indians. Am J Clin Nutr. 2001 Aug;74(2):233-41.

5. No author. Contribution of the microflora of the small intestine to the vitamin B12 nutriture of man. Nutrition Reviews. 1980 Aug;38(8):274-5.

6. Sarode R, Garewal G, Marwaha N, Marwaha RK, Varma S, Ghosh K, Mohanty D, Das KC. Pancytopenia in nutritional megaloblastic anaemia. A study from north-west India. Trop Geogr Med. 1989 Oct;41(4):331-6.

7. Antony AC. Prevalence of cobalamin (vitamin B-12) and folate deficiency in India–audi alteram partem. Am J Clin Nutr. 2001 Aug;74(2):157-9.

8. Halsted JA, Carroll J, Dehghani A, Loghmani M, Prasad A. Serum vitamin B12 concentration in dietary deficiency. Am J Clin Nutr. 1960 May-Jun;8:374-6.

9. Wokes F, Badenoch J, Sinclair HM. Human dietary deficiency of vitamin B12. Am J Clin Nutr. 1955 Sep-Oct;3(5):375-82.

10. Miyamoto E., Yabuta Y., Kwak C.S., Enomoto T., Watanabe F. Characterization of vitamin B12 compounds from Korean purple laver (Porphyra sp.) products. J. Agric. Food Chem. 2009;57:2793–2796. [PubMed

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