Vitamin B12. Molecular model of vitamin B12, also called cyanocobalamin. This vitamin has the formula C63.H90.Co.N14.O14.P. The skeleton of the molecule is shown by the wire-frame lines, with atoms at the angles and the ends. Their size is represented by the spheres. Vitamin B12 is only produced in humans and animals, and is essential for healthy reproduction of cells and tissues. Deficiency causes anaemia, a lack of healthy red blood cells, leading to weakness, vertigo and heart complications.