Supplementation, Optimal Status, and Analytical Determination of Vitamin D: Where are we Standing in 2012?
There is a growing interest for vitamin D in the medical and scientific community as well as in the public medias as illustrated
by a huge number of publications. Most experts claim that vitamin D deficiency/insufficiency is widespread with potential important
public health consequences. It may seem surprising for many persons that a deficiency in a vitamin may be so frequent in countries where
food is so diversified and easily available. In fact, vitamin D is not a vitamin stricto sensu as it is mainly synthesized in the skin under the
action of UVB rays, while its food sources are scarce. Furthermore, UVB rays are absent during a marked part of the year at latitudes
greater than 35-40°, while pollution and cloud cover reduce the number of UVB reaching the earth, and many factors such as age, skin
pigmentation, covering clothes, sun creams reduce the capacity of the skin to synthesize vitamin D3. Vitamin D must be hydroxylated to
form 1,25dihydroxyvitamin D (1,25OH2D), the active metabolite. As 1,25OH2D is released into the bloodstream and binds to a receptor
present in several distant tissues, it may be considered as a hormone, vitamin D being thus a pre-prohormone. In the present article, we
review briefly the metabolism and various effects of vitamin D as well as the vitamin D assays and vitamin D treatments. We define
vitamin D deficiency/insufficiency considering separately the population and the patient level and propose our opinion about which
patients may benefit from vitamin D testing.
Keywords: Vitamin D, 25-hydroxyvitamin D, Calcitriol, Parathyroid hormone, Immunoassay, Mass spectrometry, Reference values, METABOLISM, Calcitriol, fortified food
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