title: Effects of vitamin D binding protein phenotypes and vitamin D supplementation on serum total 25(OH)D and directly measured free 25(OH)D.
abstract: OBJECTIVE
  To determine the relationship between serum total 25-hydroxyvitamin D (25(OH)D), directly measured free 25(OH)D and calculated free 25(OH)D with regard to vitamin D-binding protein (DBP) phenotypes, sex, BMI, age and season, and their interrelationship to vitamin D supplementation.
  A randomized controlled trial with 20 000 IU of vitamin D3 per week or placebo for 12 months was designed. A total of 472 subjects, 236 in each of the intervention groups, were included in the analyses.
  
  
  METHODS
  Baseline serum concentrations and increases in serum total 25(OH)D, directly measured free 25(OH)D, calculated free 25(OH)D and DBP.
  
  
  RESULTS
  Serum total 25(OH)D and DBP concentrations were significantly lower in subjects with the phenotype Gc2/Gc2 compared to phenotypes with the Gc1S allele, and lower in males compared to females. When using directly measured free 25(OH)D, the differences related to DBP phenotypes and sexes were clearly diminished. All calculated free 25(OH)D concentrations were overestimated compared to the directly measured free 25(OH)D. Serum parathyroid hormone showed an inverse correlation with all vitamin D parameters analyzed. The increases after 12 months of vitamin D supplementation were not significantly different for any of the vitamin D parameters regardless of DBP phenotype, sex or age. Supplementation with vitamin D did not affect serum DBP.
  
  
  CONCLUSIONS
  Direct measurements of free 25(OH)D reduce the differences seen in total 25(OH)D between DBP phenotype groups and sexes, probably caused by differences in DBP concentrations. With conditions affecting serum DBP concentrations, direct measurements of free 25(OH)D should be considered.
authors.affiliation: Tromsø Endocrine Research GroupDepartment of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, NorwayDivision of Internal MedicineUniversity Hospital of North Norway, 9038 Tromsø, NorwayDivision of Head and MotionDepartment of Rheumatology, Nordland Hospital, Bodø, NorwayDivision of Diagnostic ServicesUniversity Hospital of North Norway, Tromsø, NorwayDepartment of Medical BiologyUiT The Arctic University of Norway, Tromsø, NorwayHormone LaboratoryDepartment of Medical Biochemistry, Oslo University Hospital, Oslo, Norway Tromsø Endocrine Research GroupDepartment of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, NorwayDivision of Internal MedicineUniversity Hospital of North Norway, 9038 Tromsø, NorwayDivision of Head and MotionDepartment of Rheumatology, Nordland Hospital, Bodø, NorwayDivision of Diagnostic ServicesUniversity Hospital of North Norway, Tromsø, NorwayDepartment of Medical BiologyUiT The Arctic University of Norway, Tromsø, NorwayHormone LaboratoryDepartment of Medical Biochemistry, Oslo University Hospital, Oslo, Norway stina.therese.sollid@unn.no.
authors.forename: Stina T
authors.initials: ST
authors.lastname: Sollid
authors.affiliation: Tromsø Endocrine Research GroupDepartment of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, NorwayDivision of Internal MedicineUniversity Hospital of North Norway, 9038 Tromsø, NorwayDivision of Head and MotionDepartment of Rheumatology, Nordland Hospital, Bodø, NorwayDivision of Diagnostic ServicesUniversity Hospital of North Norway, Tromsø, NorwayDepartment of Medical BiologyUiT The Arctic University of Norway, Tromsø, NorwayHormone LaboratoryDepartment of Medical Biochemistry, Oslo University Hospital, Oslo, Norway Tromsø Endocrine Research GroupDepartment of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, NorwayDivision of Internal MedicineUniversity Hospital of North Norway, 9038 Tromsø, NorwayDivision of Head and MotionDepartment of Rheumatology, Nordland Hospital, Bodø, NorwayDivision of Diagnostic ServicesUniversity Hospital of North Norway, Tromsø, NorwayDepartment of Medical BiologyUiT The Arctic University of Norway, Tromsø, NorwayHormone LaboratoryDepartment of Medical Biochemistry, Oslo University Hospital, Oslo, Norway.
authors.forename: Moira Y S
authors.initials: MY
authors.lastname: Hutchinson
authors.affiliation: Tromsø Endocrine Research GroupDepartment of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, NorwayDivision of Internal MedicineUniversity Hospital of North Norway, 9038 Tromsø, NorwayDivision of Head and MotionDepartment of Rheumatology, Nordland Hospital, Bodø, NorwayDivision of Diagnostic ServicesUniversity Hospital of North Norway, Tromsø, NorwayDepartment of Medical BiologyUiT The Arctic University of Norway, Tromsø, NorwayHormone LaboratoryDepartment of Medical Biochemistry, Oslo University Hospital, Oslo, Norway.
authors.forename: Vivian
authors.initials: V
authors.lastname: Berg
authors.affiliation: Tromsø Endocrine Research GroupDepartment of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, NorwayDivision of Internal MedicineUniversity Hospital of North Norway, 9038 Tromsø, NorwayDivision of Head and MotionDepartment of Rheumatology, Nordland Hospital, Bodø, NorwayDivision of Diagnostic ServicesUniversity Hospital of North Norway, Tromsø, NorwayDepartment of Medical BiologyUiT The Arctic University of Norway, Tromsø, NorwayHormone LaboratoryDepartment of Medical Biochemistry, Oslo University Hospital, Oslo, Norway.
authors.forename: Ole M
authors.initials: OM
authors.lastname: Fuskevåg
authors.affiliation: Tromsø Endocrine Research GroupDepartment of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, NorwayDivision of Internal MedicineUniversity Hospital of North Norway, 9038 Tromsø, NorwayDivision of Head and MotionDepartment of Rheumatology, Nordland Hospital, Bodø, NorwayDivision of Diagnostic ServicesUniversity Hospital of North Norway, Tromsø, NorwayDepartment of Medical BiologyUiT The Arctic University of Norway, Tromsø, NorwayHormone LaboratoryDepartment of Medical Biochemistry, Oslo University Hospital, Oslo, Norway Tromsø Endocrine Research GroupDepartment of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, NorwayDivision of Internal MedicineUniversity Hospital of North Norway, 9038 Tromsø, NorwayDivision of Head and MotionDepartment of Rheumatology, Nordland Hospital, Bodø, NorwayDivision of Diagnostic ServicesUniversity Hospital of North Norway, Tromsø, NorwayDepartment of Medical BiologyUiT The Arctic University of Norway, Tromsø, NorwayHormone LaboratoryDepartment of Medical Biochemistry, Oslo University Hospital, Oslo, Norway.
authors.forename: Yngve
authors.initials: Y
authors.lastname: Figenschau
authors.affiliation: Tromsø Endocrine Research GroupDepartment of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, NorwayDivision of Internal MedicineUniversity Hospital of North Norway, 9038 Tromsø, NorwayDivision of Head and MotionDepartment of Rheumatology, Nordland Hospital, Bodø, NorwayDivision of Diagnostic ServicesUniversity Hospital of North Norway, Tromsø, NorwayDepartment of Medical BiologyUiT The Arctic University of Norway, Tromsø, NorwayHormone LaboratoryDepartment of Medical Biochemistry, Oslo University Hospital, Oslo, Norway.
authors.forename: Per M
authors.initials: PM
authors.lastname: Thorsby
authors.affiliation: Tromsø Endocrine Research GroupDepartment of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, NorwayDivision of Internal MedicineUniversity Hospital of North Norway, 9038 Tromsø, NorwayDivision of Head and MotionDepartment of Rheumatology, Nordland Hospital, Bodø, NorwayDivision of Diagnostic ServicesUniversity Hospital of North Norway, Tromsø, NorwayDepartment of Medical BiologyUiT The Arctic University of Norway, Tromsø, NorwayHormone LaboratoryDepartment of Medical Biochemistry, Oslo University Hospital, Oslo, Norway Tromsø Endocrine Research GroupDepartment of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, NorwayDivision of Internal MedicineUniversity Hospital of North Norway, 9038 Tromsø, NorwayDivision of Head and MotionDepartment of Rheumatology, Nordland Hospital, Bodø, NorwayDivision of Diagnostic ServicesUniversity Hospital of North Norway, Tromsø, NorwayDepartment of Medical BiologyUiT The Arctic University of Norway, Tromsø, NorwayHormone LaboratoryDepartment of Medical Biochemistry, Oslo University Hospital, Oslo, Norway.
authors.forename: Rolf
authors.initials: R
authors.lastname: Jorde
mesh_terms: D000368:Aged; D019587:Dietary Supplements; D005260:Female; D056726:Genetic Association Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide; D011236:Prediabetic State / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding / Q000235:genetics; D014807:Vitamin D / Q000008:administration & dosage* / Q000031:analogs & derivatives* / Q000032:analysis / Q000097:blood / Q000378:metabolism; D014808:Vitamin D Deficiency / Q000235:genetics / Q000378:metabolism; D014809:Vitamin D-Binding Protein / Q000097:blood / Q000235:genetics* / Q000378:metabolism*
chemical_list: D014809:Vitamin D-Binding Protein; D014807:Vitamin D; C104450:25-hydroxyvitamin D