We wanted to discuss vitamin B12 and dispel the wrong information we often see being repeated. First of all vitamin B12 does not come from animals at all. It is the only vitamin synthesized exclusively by microorganisms. It is found in soil, plants and others and can satisfy our daily requirements with 4 g of dried purple laver or 50 gram of dried shiitake mushroom (Watanabe, Yabuta, Bito, & Teng, 2014). In addition, we can also satisfy our daily requirements in a much less practical way by eating 143 gram of dirt per day, 3.44 kg of spinach, or like our rabbit friends our own feces (Mozafar, 1994).
Just like many other animals we also make our own vitamin B12 in our guts. However, the place where we make it in our intestine is after the place that is able to absorb it, hence why we need an external source.
Our latest update on vitamin B12 can be found here.
References:
Mozafar, A. (1994). Enrichment of some B-vitamins in plants with application of organic fertilizers. Plant and Soil, 167(2), 305-311. www.jstor.org/stable/42939740.
Watanabe, F., Yabuta, Y., Bito, T., & Teng, F. (2014). Vitamin B₁₂-containing plant food sources for vegetarians. Nutrients, 6(5), 1861–1873. doi:10.3390/nu6051861