Vitamin B12, also called cobalamin, helps maintain healthy nerve cells and red blood cells, and is also needed to make DNA. Vitamin B12 is bound to the protein in food and is released by hydrochloric acid (HCl) in the stomach during digestion.
Once released, B12 combines with a substance called intrinsic factor (IF) before it is absorbed into the bloodstream. Vitamin B12 is needed for normal nerve activity, is necessary for DNA replication, and important for the formation of red blood cells.
Vitamin B12 is found primarily in red meat (grass fed beef, lamb, buffalo). It is also found in seafood including mussels, salmon, clams, crab, and shrimp, lobster, halibut and scallops as well as ostrich and yogurt.
National Institutes of Health, Office of Dietary Supplements