title: Increased plasma concentrations of vitamin D metabolites and vitamin D binding protein in women using hormonal contraceptives: a cross-sectional study.
abstract: Use of hormonal contraceptives (HC) may influence total plasma concentrations of vitamin D metabolites. A likely cause is an increased synthesis of vitamin D binding protein (VDBP). Discrepant results are reported on whether the use of HC affects free concentrations of vitamin D metabolites.
  
  
  OBJECTIVE
  In a cross-sectional study, plasma concentrations of vitamin D metabolites, VDBP, and the calculated free vitamin D index in users and non-users of HC were compared and markers of calcium and bone metabolism investigated.
  
  
  RESULTS
  75 Caucasian women aged 25-35 years were included during winter season. Compared with non-users (n = 23), users of HC (n = 52) had significantly higher plasma concentrations of 25-hydroxyvitamin D (25OHD) (median 84 interquartile range: [67-111] vs. 70 [47-83] nmol/L, p = 0.01), 1,25-dihydroxyvitamin D (1,25(OH)2D) (198 [163-241] vs. 158 [123-183] pmol/L, p = 0.01) and VDBP (358 [260-432] vs. 271 [179-302] µg/mL, p < 0.001). However, the calculated free indices (FI-25OHD and FI-1,25(OH)2D) were not significantly different between groups (p > 0.10). There were no significant differences in indices of calcium homeostasis (plasma concentrations of calcium, parathyroid hormone, and calcitonin, p > 0.21) or bone metabolism (plasma bone specific alkaline phosphatase, osteocalcin, and urinary NTX/creatinine ratio) between groups.
  
  
  CONCLUSIONS
  Use of HC is associated with 13%-25% higher concentrations of total vitamin D metabolites and VDBP. This however is not reflected in indices of calcium or bone metabolism. Use of HC should be considered in the interpretation of plasma concentrations vitamin D metabolites.
authors.affiliation: Department of Endocrinology and Internal Medicine, THG, Aarhus University Hospital, Tage Hansens Gade 2, DK, Aarhus 8000, Denmark. kristine.moller@ki.au.dk.
authors.forename: Ulla K
authors.initials: UK
authors.lastname: Møller
authors.forename: Susanna við
authors.initials: Sv
authors.lastname: Streym
authors.forename: Lars T
authors.initials: LT
authors.lastname: Jensen
authors.forename: Leif
authors.initials: L
authors.lastname: Mosekilde
authors.forename: Inez
authors.initials: I
authors.lastname: Schoenmakers
authors.forename: Shailja
authors.initials: S
authors.lastname: Nigdikar
authors.forename: Lars
authors.initials: L
authors.lastname: Rejnmark
mesh_terms: D000328:Adult; D015519:Bone Density; D002116:Calcitonin / Q000097:blood; D002118:Calcium / Q000097:blood; D003271:Contraceptive Agents, Female / Q000008:administration & dosage*; D003278:Contraceptives, Oral, Hormonal / Q000008:administration & dosage; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D010281:Parathyroid Hormone / Q000097:blood; D012621:Seasons; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014809:Vitamin D-Binding Protein / Q000097:blood*; D044465:White People
chemical_list: D003271:Contraceptive Agents, Female; D003278:Contraceptives, Oral, Hormonal; D010281:Parathyroid Hormone; D014809:Vitamin D-Binding Protein; D014807:Vitamin D; C097949:1,25-dihydroxyvitamin D; D002116:Calcitonin; C104450:25-hydroxyvitamin D; D002118:Calcium