Vitamin D is unique among essential nutrients in that it is a vitamin that has the ability to transform into a hormone. Once ingested, and in the liver, vitamin D is converted into a metabolite called 25-hydroxycholecalciferol [25-OH-D3], which is then converted into its active form in the kidneys, 1,25 dihydroxycholecalciferol [1,25-(OH)2-D3]. It is in this active form that vitamin D acts as a...