Description
A biologically inactive precursor to calcitriol converted to active metabolites in vivo; obtained from dietary sources, including fish, or formed in the epidermis via photolytic conversion of 7-dehydro cholesterol to previtamin D3 by UVB radiation, followed by isomerization to vitamin D3; can be converted to 25-hydroxy vitamin D3 in the liver by CYP2R1 before being converted to calcitriol by CYP27B1 in the kidney