ABSTRACT
Vitamin D is a hormone, with a chemical structure closely related to that of cortisol. It is o«en called the “sunshine vitamin” as it is synthesized in the skin following exposure to the ultraviolet B (UVB) in solar radiation. §ere are two forms of vitamin D, with only vitamin D3 (cholecalciferol) being photochemically produced in the skin, while vitamin D2 (ergocalciferol) is formed from ergosterol in plants, through a similar process. Both require metabolism to produce the active hormone. Humans can obtain both vitamin D3 and D2 through diet, although several recent surveys con©rm that the average diet contains low amounts. §ere is currently considerable controversy regarding the amounts of vitamin D required for human health and how these may best be obtained. While it is well known that vitamin D is essential for calcium metabolism and that de©ciency causes the severe bone disorders of rickets and osteomalacia, there are also associations with systemic and malignant disorders where cause and e¨ect are not ©rmly established.
