Introduction for the Symposia Entitled: Newly Discovered Actions of 1,25-Dihydroxyvitamin D 3 and Osteoporosis: Basis and Treatment

Vitamin D was originally discovered because the bone disease rickets was found in epidemic proportions in Northern Europe, North America, and Northern Asia at about the time the concept of the vitamins made its appearance (about 1900–1920). Sir Edward Mellanby, in reacting to the discovery of the fat-soluble vitamin A and water-soluble vitamin B by McCollum and co-workers at Wisconsin (1, 2) and Mendel and Osborne at the Connecticut Experiment Station (3), conceived that rickets might also be a nutritional disorder. By feeding dogs a diet of oatmeal and maintaining them indoors, he produced the same disease rickets prevalent in the human population (4). Because he was able to cure the disease with cod liver oil that was shown to contain fat-soluble vitamin A, Sir Edward Mellanby considered this curing of the bony disease rickets as another property of fat-soluble vitamin A. However, McCollum and co-workers then at Johns Hopkins demonstrated clearly the existence of the new antirachitic factor which he termed Vitamin D (5). In concomitant discoveries, Huldshinsky (6) found that rickets could also be cured by ultraviolet irradiation, and Steenbock (7) demonstrated that ultraviolet irradiation of not only skin but also food produced the antirachitic vitamin D. Vitamin D, therefore, produced by the irradiation of skin or by consuming vitamin D-rich oil such as cod liver oil then became known as a substance required for the mineralization of the skeleton. Over the next several decades the structure of the vitamin D compounds became known and the general physiology of vitamin D action was established (8). Thus, vitamin D stimulates the intestine to absorb calcium and secondarily phosphorus. It was also found to be responsible for the mobilization of calcium from bone (9), and more recently was found to stimulate renal reabsorption of calcium (10).