Vitamin B12 supports a variety of critical systems in the body, including red blood cell production, DNA synthesis and neurological function.  The version of vitamin B12 we use in Soylent is Cyanocobalamin, a synthetic form of vitamin B12.
How it works in the body
When Vitamin B12 is ingested, salivary glands secrete haptocorrin (also known as transcobalamin-1), which bonds to cyanocobalamin to protect it and prevent it from being broken down before it can be absorbed in the ileum (part of the small intestine).
After passing through the stomach, the haptocorrin-B12 complex reaches the duodenum, the first part of the small intestine. In the duodenum, haptocorrin is separated from cyanocobalamin and a transport protein called the Intrinsic Factor attaches to cyanocobalamin. The compound then continues its journey through the small intestine, eventually reaching the ileum, where it is absorbed. Without the attached intrinsic factor, B12 cannot be absorbed in the small intestine.
 Silverthorn, Dee Unglaub. "The Digestive System." In Human Physiology An Integrated Approach, 714. Sixth Edition ed. Pearson Education, 2013.
 Stipanuk, Martha H., and Marie A. Caudill. "Folate, Choline, Vitamin B12, and Vitamin B6." In Biochemical, Physiological, and Molecular Aspects of Human Nutrition, 590. Third Edition ed. St. Louis: Elsevier, 2013.