Previtamin D3 is an intermediate in the synthesis of the calcitriol precursor vitamin D3 .1,2 It is formed from 7-dehydro cholesterol in the epidermis via photolytic conversion by UVB radiation and is isomerized to vitamin D3. The rate of previtamin D3 synthesis is dependent on the solar zenith angle, which is affected by the latitude, season, and time of day. It is also dependent on the level of skin pigmentation and age, among other factors, with a negative correlation to higher pigmentation and age.3,2,4
1.Rosen, C.J.Vitamin D insufficiencyN. Engl. J. Med.364(3)248-254(2011) 2.Chen, T.C., Chimeh, F., Lu, Z., et al.Factors that influence the cutaneous synthesis and dietary sources of vitamin DArch. Biochem. Biophys.460(2)213-217(2007) 3.Holick, M.F., Chen, T.C., Lu, Z., et al.Vitamin D and skin physiology: A D-lightful storyJ. Bone Miner. Res.22 Suppl 2.V28-33(2007) 4.Webb, A.R.Who, what, where and when-influences on cutaneous vitamin D synthesisProg. Biophys. Mol. Biol.92(1)17-25(2006)