Are Intestinal Bacteria a Reliable Source of B12?

Summary: Given that many otherwise healthy vegans develop B12 deficiency when not supplementing their diets with B12, intestinal bacteria cannot be relied upon to prevent B12 deficiency in vegans.

Are raw foodists or people who eat fermented foods exceptions? No. See the section B12 Status: Raw Foodist Vegans.

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. It is surmised that eating feces allows them to obtain B12 on their diets of plant foods. Although I believe this to be true, it has not been verified beyond a reasonable doubt.

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. 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.

Bacteria in the Small Intestine

B12 deficiency has been found with relatively high frequency among vegetarian Indian immigrants in England, while it is supposedly uncommon among native Indians with identical dietary patterns.^1,2 Healthy Indian subjects have a more extensive amount of bacteria in their small intestine than people in the West.¹

Albert et al.¹ (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 Reviews³ (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 there are few vegans in India and there is also evidence that B12 deficiency is not so uncommon there (see Table below),² especially in lower economic, lacto-ovo vegetarians.⁴