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BACKGROUND	Little is known about how the genetic variation in vitamin D modulating genes influences ultraviolet ( UV ) B-induced 25-hydroxyvitamin D [ 25 ( OH ) D ] concentrations .
BACKGROUND	In the Food with vitamin D ( VitmaD ) study , we showed that common genetic variants rs10741657 and rs10766197 in 25-hydroxylase ( CYP2R1 ) and rs842999 and rs4588 in vitamin D binding protein ( GC ) predict 25 ( OH ) D concentrations at late summer and after 6-mo consumption of cholecalciferol ( vitamin D ) - fortified bread and milk .
OBJECTIVE	In the current study , called the Vitamin D in genes ( VitDgen ) study , we analyzed associations between the increase in 25 ( OH ) D concentrations after a given dose of artificial UVB irradiation and 25 single nucleotide polymorphisms located in or near genes involved in vitamin D synthesis , transport , activation , or degradation as previously described for the VitmaD study .
OBJECTIVE	Second , we aimed to determine whether the genetic variations in CYP2R1 and GC have similar effects on 25 ( OH ) D concentrations after artificial UVB irradiation and supplementation by vitamin D-fortified bread and milk .
METHODS	The VitDgen study includes 92 healthy Danes who received 4 whole-body UVB treatments with a total dose of 6 or 7.5 standard erythema doses during a 10-d period in winter .
METHODS	The VitmaD study included 201 healthy Danish families who were given vitamin D-fortified bread and milk or placebo for 6 mo during the winter .
RESULTS	After UVB treatments , rs10741657 in CYP2R1 and rs4588 in GC predicted UVB-induced 25 ( OH ) D concentrations as previously shown in the VitmaD study .
RESULTS	Compared with noncarriers , carriers of 4 risk alleles of rs10741657 and rs4588 had lowest concentrations and smallest increases in 25 ( OH ) D concentrations after 4 UVB treatments and largest decreases in 25 ( OH ) D concentrations after 6-mo consumption of vitamin D-fortified bread and milk .
CONCLUSIONS	Common genetic variants in the CYP2R1 and GC genes modify 25 ( OH ) D concentrations in the same manner after artificial UVB-induced vitamin D and consumption of vitamin D-fortified bread and milk .

