Vitamin B12 and Human Nutritional Evolution

I once believed and argued that the fact that humans require vitamin B-12 provided substantial support for the idea that humans have a biological requirement for dietary meat.  My reasoning went thus:

Humans require vitamin B-12, and only animal products reliably provide natural bioactive vitamin B-12, therefore we must be adapted to and dependent upon meat-eating.

I have since realized that I made a few mistakes here.  Although we definitely require B-12, animal products are not the only reliable sources of natural bioactive B12, and human B-12 metabolism provides evidence that our ancestors adapted to an environment/diet that had a low availability of B-12 compared to currently recommended daily reference intakes.

Human B-12 Metabolism

Humans have enterohepatic circulation of vitamin B-12.[1 ] As noted by Herbert [2 ], this can allow an initially B-12 replete adult go 20-30 years without vitamin B-12 intake:

“The enterohepatic circulation of vitamin B-12 is very important in vitamin B-12 economy and homeostasis (27). Nonvegetarians normally eat 2-6 mcg of vitamin B-12/d and excrete from their liver into the intestine via their bile 5-10 mcg of vitamin B-12/d. If they have no gastric, pancreatic, or small bowel dysfunction interfering with reabsorption, their bodies reabsorb ~3-5 mcg of bile vitamin B-12/d. Because of this, an efficient enterohepatic circulation keeps the adult vegan, who eats very little vitamin B-12, from developing vitamin B-12 deficiency disease for 20-30 y (27) because even as body stores fall and daily bile vitamin B-12 output falls with body stores to as low as 1 mcg, the percentage of bile vitamin B-12 reabsorbed rises to close to 100%, so that the whole microgram is reabsorbed.”

What kind of environment/diet would naturally favor the survival of humans having such efficient recycling of vitamin B-12 but not of other B-complex vitamins? 

As a general principle, if an organism subsists on a diet with a low availability of a certain essential nutrient, it needs mechanisms for increasing absorption and retention of that nutrient, to prevent deficiency.  On the other hand, if an organism subsists on a diet with a very high availability of a certain essential nutrient, then it needs mechanisms for reducing absorption, detoxifying, and eliminating that nutrient.

Put in natural selection terms, only an ancient environment/diet with a low B-12 availability would have favored the survival and reproduction of humans who could recycle B-12 very efficiently.  An ancient environment/diet with a high B-12 availability would have made such a capacity unnecessary; on the contrary, an environment with a high availability of vitamin B-12 would have favored those who were less efficient at using B-12, or those who deliberately excreted excessive B-12 (in order to prevent B-12 accumulation and toxicity).

Thus, modern human B-12 metabolism suggests that modern humans are adapted to a diet that provides B-12 in less than required amounts on a daily basis, while occasionally providing larger doses in excess of requirements.  

Currently the National Academy of Sciences recommends that adults consume 2.4 mcg of B12 daily.  They calculated that this covers the needs of 98 percent of individuals, but most of us require less than this.  The following table shows the B12 contents of commonly consumed animal products:

Three ounces of beef or salmon provides the recommended intake, and three ounces of shellfish substantially exceeds the recommended 2.4 mcg.  In contrast, one would have to consume 24 ounces of chicken or turkey daily to ingest 2.4 mcg of B12. 

Non-animal B-12 Sources

As I said above, I previously accepted that only animal products reliably provide natural vitamin B-12.  Although this is a common belief, and probably a good general rule in modern industrialized nations, I think we have significant evidence that pre-industrial humans had other significant sources of vitamin B-12.

First, although animal products provide the most common vector for delivery of B-12 in modern industrialized nations, only microbes produce vitamin B-12. [3] Many microbes have the ability to produce B-12, among them the following genera: Aerobacter, Agrobacterium, Alcaligenes, Azotobacter, Bacillus, Clostridium, Corynebacterium, Flavobacterium, Micromonospora, Mycobacterium, Norcardia, Propionibacterium, Protaminobacter, Proteus, Pseudomonas, Rhizobium, Salmonella, Serratia, Streptomyces, Streptococcus and Xanthomonas. 

Bacillus megaterium is a common soil bacteria, not pathogenic to humans, and a producer of vitamin B-12.[4]  According to Patricia Vany of the Department of Biological Sciences at NIU, B. megaterium occurs in human breast milk.[15, third slide] 

Lactobacillus reuturi, a member of the gastrointestinal ecosystems of humans, poultry, swine, and other animals, and present in sourdough culture, produces vitamin B-12. [5]

Albert et al reported “the human small intestine also often harbours a considerable microflora and this is even more extensive in apparently healthy southern Indian subjects. We now show that at least two groups of organisms in the small bowel, Pseudomonas and Klebsiella sp., may synthesize significant amounts of the vitamin.”[6]

In 1995 Suzuki reported that the marine algae, nori, prevented all signs of B12 deficiency symptoms in 6 vegan children he studied:

“A nutritional analysis was conducted on the dietary intake of a group of 6 vegan children aged 7 to 14 who had been living on a vegan diet including brown rice for from 4 to 10
years, and on that of an age-matched control group. In addition, their serum vitamin B12 levels and other data (red blood cell count, hematocrit, hemoglobin, etc.) were determined in the laboratory. In vegans' diets, 2-4 g of nori (dried laver), which contained B12, were consumed daily. Not a single case of symptoms due to B12 deficiency was found. There were no statistically significant differences between the two groups with respect to any of the examination data, including B12 levels (p < 0.05). Therefore, consumption of nori may keep vegans from suffering B12 deficiency.” [7] 

[In 2005 Croft et al reported that algae acquire vitamin B12 through a symbiotic relationship with bacteria. (14) ]

In 2009 Koyyalamudi et al [8] reported that the common white button mushroom can provide vitamin B12 of value equivalent to that found in beef, beef liver, salmon, egg, and milk (not analogues).  Koyyalamudi et al determined that the mushrooms probably absorbed the B12 from bacteria inhabiting their growth medium:

“High concentrations of vitamin B12 were also detected in the flush mushrooms including cups and flats.  HPLC and mass spectrometry showed vitamin B12 retention time and mass spectra identical to those of the standard vitamin B12 and those of food products
including beef, beef liver, salmon, egg, and milk but not of the pseudovitamin B12, an inactive corrinoid in humans. The results suggest that the consumer may benefit from the consumption of mushroom to increase intake of this vitamin in the diet.” [8]

In 1994, Mozafar reported that spinach leaves and barley seeds grown on soil fertilized with organic matter or isolated B12 take up vitamin B12 into their tissues from the soil.  The spinach leaves and barley kernels were thoroughly washed with distilled water before being tested for B12 content, so this was not a case of finding B12 on soiled plants.  Their testing confirmed that these plants contained active B12, not inactive analogues.[9]

In summary, it appears that non-pathogenic soil microbes, human small intestinal bacteria, lactobacilli from fermented foods, some sea algae, common mushrooms, and plants grown on soil fertilized with animal manure can all can provide biologically active B12.   Any of these could have served as ongoing sources of B12 for prehistoric human ancestors, but modern circumstances may make these non-animal sources of B12 unreliable for modern humans.

I think it safe to assume that our prehistoric ancestors had more contact with soil than we do, sitting on it, sleeping on it, digging in it, and drawing water from sources in contact with the soil.  Humans like other primates are apt to touch their own lips from time to time, providing a vector by which soil microbes could enter the human gut.

Humans living in modern industrialized nations typically ingest multiple courses of oral antibiotics over a lifetime, reducing or eliminating the population of B12-producing bacteria residing in the small intestine.   All of our prehistoric ancestors would have been breast fed and probably kissed often, which transmits flora from one generation to another, and this transmission would not have been interrupted by antibiotic treatments.

Fermentation of plant foods, particularly fruits, occurs spontaneously in nature,  providing another route by which our ancestors may have ingested B12-producing lactobacilli.  Our ancestors almost certainly consumed any edible wild mushrooms and all of the plants they ate grew in soils teaming with bacteria and fertilized by fermented organic wastes, providing another B12 source.

All of this information suggests that modern hygiene, indoor lifestyles, antibiotics, and use of chemical rather than biomass fertilizers in farming have reduced the amount of B12 available to humans in modern urban environments from non-animal sources. 

Thus, the low availability of B12 from non-animal sources in modern urban environments is an artifact not reflective of preindustrial environments, and it appears probable that our prehistoric ancestors had more non-animal sources present in their environment, like the southern Indians studied by Albert et al.[6] 

My Fallacious Appeal to 'Nature'

When I previously argued that meat-eating is the 'natural' way to get B12, I committed the fallacy of appeal to nature. 


The problem here lies in these underlying assumptions:  1) all 'natural' behaviors are 'health-promoting' behaviors for modern urban humans,  and 2)  all 'unnatural' behaviors are unhealthful.

Consider these questions:

 

Is it natural for humans to wear clothing?  Does wearing clothing promote better health in some circumstances?  (Imagine people living in Minnesota rejecting clothing because their African ancestors didn't wear any.)

 

Is it natural for humans to live in igloos in the arctic circle?  Does living in igloos in the arctic circle promote the best of health?

 

Is it natural for humans to live in natural caves?  Do humans have the best possible health when living in natural caves?  Is a natural cave the best possible human shelter?

 

Is it natural for humans to commit homicide, engage in war, or eat human flesh?  Do any of these promote health? 

 

If all you mean by 'natural' is 'spontaneously occurring,' then all human behaviors are 'natural.' 

But is the 'natural' choice of our ancestors the best possible choice for modern humans of the present day?

Simply put, the fact that our ancestors did something then does not tell us that it is the best thing for us to do now.

The fact that our ancestors obtained B12 by a 'natural' route (eating meat) does not tell me that this is the optimal way for me to get B12 in our modern circumstances. 

The Nature of B12 Supplements

Artificial synthesis of B12 requires about 70 synthesis steps, making it impractical as a method for commercial production of B12.  “Therefore, today vitamin B12 is exclusively produced by biosynthetic fermentation processes, using selected and genetically optimized micro-organisms.” [10]

In other words, we cultivate, feed and breed living microbes so that they will produce the nutrient we want.  This practice seems similar to cultivating cattle to produce protein or B12.  If the former is ‘artificial,’ so is the latter.

Tablets of microbially synthesized B12, burgers of ground beef, capsules of vitamin D extracted from sheep’s hair, and tortillas made from corn are all end products of humans processing a raw material into a form that humans can conveniently consume.   If you reject B12 tablets as ‘unnatural,’ you should similarly reject ground beef burgers and vitamin D capsules.

The information above indicates that modern antibiotics and hygiene have reduced or eliminated intestinal flora that would otherwise produce B12 for us, and modern agricultural practices have reduced the B12 content of plant foods.  Similarly, modern indoor lifestyles have reduced our endogenous production of vitamin D.  We can reasonably use supplements to correct for these technology-induced deficiencies.

In short,  B12 supplements are the most reliable source of natural B12 in the modern environment.

Microbial B12 Supplements Recommended To People Past 50 Years Of Age

The Linus Pauling Institute at Oregon State University recommends that all people (including omnivores) over the age of 50 take a B12 supplement:

“Also, individuals over the age of 50 should obtain their vitamin B12 in supplements or fortified foods like fortified cereal because of the increased likelihood of food-bound vitamin B12 malabsorption.”[11]

In the publication Dietary Reference Intakes [12 ], the National Academy of Science Food and Nutrition Board concurs:

So these sources do not consider animal foods to be reliable sources of B12 for those of us more than 50 years of age.

Do we reject this advice because it is not 'natural' to take supplements?

Some B12 Options


Modern humans typically use their minds to identify their requirements for health and comfort, then develop and use appropriate technology to provide those requirements in the most efficient, safest possible way.  

Thanks to microbe-ranching, each modern urban human now has the opportunity to decide which of at least 3 courses s/he would prefer to take to ensure achievement of a healthy B12 status.

Course 1:  Obtain B12 directly from a cultivated microbial source, the production of which requires relatively little land and water and produces no urine or feces.  This source is free of saturated fats, cholesterol, heterocyclic amines, lipid peroxides, pathogenic organisms, or antigenic Neu 5Gc sialic acid (a suspect in human cancers and autoimmunity, found only in mammal’s products, 13 ).

Course 2: Obtain B12  from animal products, the production of which requires enormous amounts of land and water and produces tremendous amounts of urine and feces requiring safe disposal.  This source also supplies saturated fats and cholesterol,  heterocyclic amines (cooked meat), and lipid peroxides (cooked fat),  and is frequently contaminated with various potential pathogens (E. coli 0157:H7, MAR bacteria, salmonella, vibrio, etc.).  Red meats and mammalian milks also provide antigenic Neu5Gc sialic acid. [13]

As noted above, current science indicates that Course 2 is probably not reliable for people more than 50 years of age.

Course 3:  Use both B12 supplements and animal products.

Take your pick, or perhaps you will discover another way.

Thanks to the author/producer of the Primitive Nutrition video series for alerting me to the article on the B12 content mushrooms used in this post.