Vitamin D: part I; from plankton and calcified skeletons (500 million years ago) to rickets

The vitamin D history started early in the evolution of life (billion years ago) as a photochemical reaction producing an inert molecule. During the early evolution of vertebrates, this molecule became essential for calcium and bone homeostasis of terrestrial animals and arrived to the status of hormone. Phytoplankton, zooplankton, and most plants and animals that are exposed to sunlight have the capacity to make vitamin D. Vitamin D is critically important for the development, growth, and maintenance of a healthy skeleton from birth until death. The major function of vitamin D is to maintain calcium homeostasis. It accomplishes this by increasing the efficiency of the intestine to absorb dietary calcium. When there is inadequate calcium in the diet to satisfy the body's calcium requirement, vitamin D communicates to the osteoblasts that signal osteoclast precursors to mature and dissolve the calcium stored in the bone. The typical "vitamin D-deficiency" disorder was observed for growing children in the west and south of England in the early 1600s. This disease was described by Glisson and named "rickets" (known also as "the English disease") and was observed with epidemic proportions in northern Europe and North America. The corrections of deformities of rickets were at the origin of the name "orthopedia" and of the technique of osteotomies.