Odd question, I know. I seem to remember it calculating to roughly one pound of soil a day. I use the information as a response to vegans who, while meaning well, ignore the science of how B12 is created.
B12 is obtained from bacteria capable of its production, the only two having all the necessary enzymes are Propionibacterium freudenreichii (A genetically-engineered strain of this is used to make B12 commercially) and Lactobacillus reuteri (naturally found in human intestine, but in the large bowel, beyond the point of absorption). Other bacteria collaborate to produce B12. Further, these organisms are mostly anaerobic. B12 is not obtained not from the soil itself, but rather from these bacteria present in the soil by way of excreta. Since these bacteria are exposed to aerobic conditions when in the soil, their B12 production stops, so soil therefore is more likely to provide little to no B12.
In soil containing fresh excreta and a high load of these bacteria, about 100g of the earth provides 1mcg (0.02 to 10 mcg) of B12 (Mozafar, 1994), of which 5-10% would be of absorbable form, and of this, only about 50% is absorbed. This translates to 0.005 mcg of B12 for 100g of soil consumed. The RDA of B12 for adults is 2.5mcg, so the required amount of soil would be 5 kilograms per day.
Thanks for the data, Ashwath Ramji. 5kg is far higher than the estimate that I had done years ago. I think I was using conservative estimates.
You’re welcome. Its possible my calculations are incorrect though, Math has never been a strong suit! Also, there is a wide range of possible B12 content, perhaps you used the upper limit when you did your calculations - but even then, would still be more soil than anyone could swallow.
The world of micronutrients still has many gaps, and the specific case of vitamin b12 is particularly complex given the clinical importance of its levels, which are low, but also high. In this sense, in complement to the debate question, I want to share with you the following manuscript detailing the aspects associated with high levels of vitamin b12.
Article Hipervitaminosis B12 una mirada desde la atención primaria