The vitamin D deficiency pandemic and consequences for nonskeletal health: Mechanisms of action

Vitamin D, the sunshine vitamin, is important for childhood bone health. Over the past two decades, it is now recognized that vitamin D not only is important for calcium metabolism and maintenance of bone health throughout life, but also plays an important role in reducing risk of many chronic diseases including type I diabetes, multiple sclerosis, rheumatoid arthritis, deadly cancers, heart disease and infectious diseases. How vitamin D is able to play such an important role in health is based on observation that all tissues and cells in the body have a vitamin D receptor, and, thus, respond to its active form 1,25-dihydroxyvitamin D. However, this did not explain how living at higher latitudes and being at risk of vitamin D deficiency increased risk of these deadly diseases since it was also known that the 1,25-dihydroxyvitamin D levels are normal or even elevated when a person is vitamin D insufficient. Moreover, increased intake of vitamin D or exposure to more sunlight will not induce the kidneys to produce more 1,25-dihydroxyvitamin D. The revelation that the colon, breast, prostate, macrophages and skin among other organs have the enzymatic machinery to produce 1,25-dihydroxyvitamin D provides further insight as to how vitamin D plays such an essential role for overall health and well being. This review will put into perspective many of the new biologic actions of vitamin D and on how 1,25-dihydroxyvitamin D is able to regulate directly or indirectly more than 200 different genes that are responsible for a wide variety of biologic processes.