Vitamin B12, or cobalamin, is an essential nutrient many normal and healthy body functions. In particular, it is critical in the production of methionine, an essential amino acid of all proteins. Cells that undergo constant and rapid production are better produced in the presence of B12 (and methionine): Red blood cells Skin and hair Muscle cells (athletes) Cancer cells, included. As we look toward maintaining healthy skin, B vitamins are very important. Hyaluronic acid (B5)