We investigated whether 41 candidate single nucleotide polymorphisms ( SNPs ) in vitamin D and calcium pathway genes ( GC , DHCR7 , CYP2R1 , CYP27B1 , CYP24A1 , VDR , and CASR ) are associated with [ 25 ( OH ) D ] or modify the increase in [ 25 ( OH ) D ] from vitamin D3 supplementation .