The skin's exposure to UV rays from sunlight induces the photolytic cleavage of 7-dehydrocholesterol to previtamin D3. This is followed by thermal isomerization to form vitamin D3 (VD3, cholecalciferol) (Holick et al. 1977).
Holick, MF, Frommer, JE, McNeill, SC, Richtand, NM, Henley, JW, Potts JT, Jr
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