1. The vitamin D questions: How much do you need and how should you get it? 
Deon Wolpowitz, MD, PhD, Barbara A. Gilchrest, MD 
Journal of the American Academy of Dermatology 
Volume 54, Issue 2, Pages (February 2006)
DOI: /j.jaad
Copyright © 2006 American Academy of Dermatology, Inc. Terms and Conditions

2. Fig 1
Sources, sites, and processing of vitamin (vit) D metabolites. In skin (step 1), 7-dehydrocholesterol (DHC) is converted by UVB into previt D3, that further UVB exposure converts into biologically inactive products tachysterol and lumisterol. In this way, tachysterol and lumisterol formation acts as biologic safety valve to prevent UVB-induced vit D toxicity. Thermal isomerization converts previt D3 into vit D3, which then enters into circulation. Vit D3/D2 also enters circulation by absorption through gastrointestinal (GI) tract (step 2). Vit D3/D2, bound to vit D–binding protein, are transported to liver (step 3) where CYP27A1 converts them to the biologically inactive 25-OH vit D. 25-OH vit D is carried to kidney (step 4) where it is converted to 1,25-(OH)2 vit D, the biologically active metabolite of vit D metabolism. Finally, both 25-OH vit D and 1,25-(OH)2 vit D are metabolized to biologically inactive products by ubiquitous enzyme, CYP24.
Journal of the American Academy of Dermatology  , DOI: ( /j.jaad )
Copyright © 2006 American Academy of Dermatology, Inc. Terms and Conditions

3. Fig 2
Cutaneous vitamin (vit) D synthesis cannot be dissociated from harmful effects of UV radiation. Dashed and dotted line (blue) shows spectrum of previt D3 formation obtained from plotting reciprocal of photoenergy (1/w cm−2) (adapted122 by converting from a linear to power-of-10 scale). Dashed line (green) represents both action spectrum of induction of squamous cell carcinoma in human beings mathematically derived from experimental data obtained from murine skin, and wavelength dependence of induction of DNA damage, in this case cyclobutane pyrimidine dimers, in human skin (adapted121). Solid line (red) shows erythema action spectrum from human skin (m2/J) (adapted26). Note that peaks of these 3 curves all occur within UVB spectrum ( nm) (dashed gray lines).
Journal of the American Academy of Dermatology  , DOI: ( /j.jaad )
Copyright © 2006 American Academy of Dermatology, Inc. Terms and Conditions