Chapter 057. Photosensitivity and Other Reactions to Light (Part 3)
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Vitamin D Photochemistry Cutaneous exposure to UV-B causes photolysis of epidermal 7dehydrocholesterol converting it to pre-vitamin D3, which then undergoes a temperature-dependent isomerization to form the stable hormone vitamin D3. This compound then diffuses to the dermal vasculature and circulates systemically where it is converted to the functional hormone 1,25-dihydroxyvitamin D3[1,25(OH)2D3]. Vitamin D metabolites from the circulation or those produced in the skin itself can augment epidermal differentiation signaling. Controversy exists regarding the importance of sun exposure in vitamin D homeostasis. At present, it is important to emphasize that the use of sunscreens does not substantially diminish vitamin D...
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