Vitamin B12 (Part Deux)

This complex and confusing mass of chemical scribble to the right is B12. Most publications regarding vitamin B12 will neglect to reflect on a few fascinating facts regarding the molecule. Complex as it looks, the molecule itself is speculated to have been around for 3 to 4 billion years. That’s billion years.

The next fascinating factoid regarding B12 is it’s made by some our bacterial arch enemies, including Klebsiella pneumoniae, Salmonella typhimurium and E-coli (if offered a precursor, cobinamide). Not arch enemies in a strict sense, as many of the colonic bacteria indeed reside happily in our colons coexisting in harmony with us and making loads of vitamin B12 (only to have us excrete it), but arch enemies in the sense that if given the opportunity, in a weakened host, will kill us.

Is this beginning to seem like a good bacteria/bad bacteria story? If they coexist in our colons, performing innocent fermentation functions, living happy healthy lives, but have the capacity to cause disease and death in their human hosts, all the while producing a molecule critical to our survival, what would you call that? That’s more than symbiosis, that’s co-dependence.

Absorption and Disposition of B12
When again considering the sources of B12 many would point to those sources as evidence of animal consumption for many millions of years. Although geophagy and coprophagy are possible sources of the vitamin, there’s minimal evidence of either from anthropological data. And while strict vegans might argue the point, that leaves meat eating as the only consistent source of B12 over the history of man.

The absorption of vitamin B12 from dietary sources requires a chorus of activities and proteins to effect the separation and transport through the intestinal wall and into vital tissues, organs and cells. After chewing a B12 containing food a molecule called Haptocorrin binds B12 to shuttle it through the upper stomach and small intestine to keep it safe from either acid damage or bacterial consumption. In the small intestine a protein call Intrinsic Factor (IF)—which is secreted by the stomach—binds B12 and shuttles it to a receptor in the ileum. From the receptor, the IF-B12 complex is absorbed by endocytosis and the B12 is transferred to another shuttle protein called transcobalamin-II. The transcobolomin-II B12 complex is taken to tissues and taken up by an as yet unknown mechanism into cells.

B12 body stores are adequate enough to last for 3-5 years without any intake before a deficiency state sets in. Those as greatest risk of a B12 deficiency are individuals with minimal animal food sources, such as vegans and strict vegetarians, and the elderly consuming a series of “tea and toast” style meals as well as those with missing IF or short guts due to surgery.

A deficiency of B12 leads to a host of problems the least of which is a severe anemia. The anemia can take two forms:

1. Pernicious Anemia: Lack of IF

2. Megaloblastic Anemia: Lack of dietary B12

Deficiency of B12 can lead to devastating and permanent central nervous system degeneration with ataxia, numbness and spinal cord degeneration.

Note: I'll be traveling for a week or so.