Ingredient name: Cyanocobalamin (B12)
Chemical Formula: C63H88CoN14O14P
Amount included in 1 pouch of Soylent: 6 ug
National Institute of Health Daily Recommended Intake: 2.4 ug for males and females 14-years-old and up.
When Vitamin B12 is ingested, salivary glands secrete haptocorrin (also known as transcobalamin-1), which bonds to cyanocobalamin in order 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 can not be absorbed in the small intestine.
Reason this form chosen
Among the several forms of vitamin B12 in existence, cyanocobalamin is the most cost-effective. At this time, research has not shown significant differences in the bioavailability of the various forms of vitamin B12. When taken solely as a supplement (in pill form, for example), there is concern that low quantities of cyanocobalamin are bonded to the Intrinsic Factor (the transport protein which enables cyanocobalamin to be absorbed in the small intestine). However, when consumed as part of a meal (as it is in Soylent), the stomach naturally releases sufficient quantities of the Intrinsic Factor to bind to 2 to 4 ug of cyanocobalamin.
The cyanocobalamin in the vitamin blend is produced by DSM Fortitech.
Some users have expressed concern about the relation between cyanocobalamin and cyanide (which is merely a carbon atom triple bonded to a nitrogen atom). While cyanocobalamin does contain several carbon atoms with triple bonds to nitrogen atoms, the greater molecular structure in no way poses the same toxic threats as a cyanide ion. Cyanocobalamin is a GRAS- (Generally Recognized As Safe) approved substance by the FDA.
 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.
 See footnote 3, "Biochemical, Physiological, and Molecular Aspects of Human Nutrition."