Calciol is a hydroxy seco-steroid that is (5Z,7E)-9,10-secocholesta-5,7,10(19)-triene in which the pro-S hydrogen at position 3 has been replaced by a hydroxy group. It is the inactive form of vitamin D3, being hydroxylated in the liver to calcidiol (25-hydroxyvitamin D3), which is then further hydroxylated in the kidney to give calcitriol (1,25-dihydroxyvitamin D3), the active hormone. It has a role as a geroprotector and a human metabolite. It is a steroid hormone, a secondary alcohol, a seco-cholestane, a hydroxy seco-steroid and a member of D3 vitamins.