3. Vitamin D

Short Description
Vitamin D is required to maintain normal blood levels of calcium and phos- … Vitamin D achieves this after its conversion to the active form 1,25- …

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3. Vitamin D
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3.1 Role of vitamin D in human metabolic processes
Vitamin D is required to maintain normal blood levels of calcium and phosphate,
which are in turn needed for the normal mineralization of bone, muscle
contraction, nerve conduction, and general cellular function in all cells of the
body. Vitamin D achieves this after its conversion to the active form 1,25-
dihydroxyvitamin D [1,25-(OH)2D], or calcitriol. This active form regulates
the transcription of a number of vitamin D-dependent genes which code for
calcium-transporting proteins and bone matrix proteins.
Vitamin D also modulates the transcription of cell cycle proteins, which
decrease cell proliferation and increase cell differentiation of a number of specialized
cells of the body (e.g. osteoclastic precursors, enterocytes, keratinocytes).
This property may explain the actions of vitamin D in bone
resorption, intestinal calcium transport, and skin. Vitamin D also possesses
immunomodulatory properties that may alter responses to infections in vivo.
These cell differentiating and immunomodulatory properties underlie the
reason why vitamin D derivatives are now used successfully in the treatment
of psoriasis and other skin disorders.
3.1.1 Overview of vitamin D metabolism
Vitamin D, a seco-steroid, can either be…