Over the last two decades the sun has become our enemy. News reports caution against any unprotected exposure to this menace and health experts plead with us to get off the beach and under some sort of cover. SPF (originally short for Sun Protection Factor) has become a noun and skin care products (and even clothing) are chock full of it. Skin cancer is predicted to become an epidemic, and exposure to the sun is to blame.

While there is certainly ample evidence that excessive ultraviolet exposure is a risk factor for the development of melanoma (and may cause premature aging of the skin), there is another side to that coin. When our skin is exposed to ultraviolet light, it produces a crucial chemical compound erroneously called Vitamin D. Without sufficient ultraviolet exposure (and a lack of adequate dietary Vitamin D to make up for the lost endogenous production), a host of systems in the human body cease to function properly, if at all.

As the Industrial Revolution took hold in Europe and the previously agrarian population began to move to growing, smoggy cities in order to find industrial jobs, a mysterious affliction began to strike the children of industrial workers in epidemic proportions. Called ‘rickets', it was characterized by skeletal bones that did not harden but remained cartilaginous. Children stricken with rickets were slow to crawl and walk and had telltale deformities in their leg bones. Rachitic children also often suffered from painful spasms in their hands and feet, difficulty breathing and persistent nausea. In severe cases, rickets was fatal.

In 1822 a Polish physician named Jedrzej Sniadecki noted an odd geographic distribution of rickets cases in and around Warsaw . Children living in the city itself were much more likely to develop rickets than those living in the outskirts or in the rural areas outside of the city. He concluded (correctly) that rickets was related to lack of exposure to sunshine. 1 He published his findings in Polish, however, and they were not widely read. Rickets continued to plague the industrial cities of Europe and the United States for another century. The only other cure that proved effective (but was not widely promoted by the physicians of the day) was the folk tradition of giving cod liver oil to children upon weaning, to provide additional fats. What was not known is that cod liver oil is an excellent source of Vitamin D.

By the end of the 19 th century, rickets had become a real problem (in Britain and Scotland especially), and there was great interest in finding a cure. In 1892, British scientist T.A. Palm rediscovered the geographic distribution of rickets that Sniadecki had noted seventy years earlier and in 1919, German scientists showed that rickets could be cured by exposure to artificially produced ultraviolet light. In 1922 Elmer McCollum, working at Johns Hopkins University in Baltimore identified a fat-soluble constituent in cod liver oil that could cure rickets. Following the alphabetical designation of vitamins A, B and C all isolated earlier, McCollum dubbed this new substance Vitamin D. 2