Sunscreen and vitamin D: Part I.

It is so ubiquitous in our medicine drawers, as a supplement and as a therapy, that we hardly give a thought to the process of its discovery. It feels as if we have always had vitamin D. Our early ancestors were thought to have had darkly pigmented skin and to have migrated out of Africa some 70,000 to 60,000 years ago. With their migration, they evolved to have lighter skin, thereby losing some of their sun protection. The rickets epidemic in early industrial Europe prompted the search for its cure, leading to the subsequent discovery of vitamin D and its connection to sunlight. Its discovery (vitamin D is better viewed as a steroid hormone) is a storied one and illustrates the often arduous trial-and-error work that scientists usually undertake to establish a new concept.