title: Effects of High-Dose Vitamin D2 Versus D3 on Total and Free 25-Hydroxyvitamin D and Markers of Calcium Balance.
abstract: Controversy persists over: 1) how best to restore low serum 25-hydroxyvitamin D (25D) levels (vitamin D2 [D2] vs vitamin D3 [D3]); 2) how best to define vitamin D status (total [protein-bound + free] vs free 25D); and 3) how best to assess the bioactivity of free 25D.
  
  
  
  To assess: 1) the effects of D2 vs D3 on serum total and free 25D; and 2) whether change in intact PTH (iPTH) is more strongly associated with change in total vs free 25D.
  
  
  
  Participants previously enrolled in a D2 vs D3 trial were matched for age, body mass index, and race/ethnicity. Participants received 50 000 IU of D2 or D3 twice weekly for 5 weeks, followed by a 5-week equilibration period. Biochemical assessment was performed at baseline and at 10 weeks.
  
  
  
  Thirty-eight adults (19 D2 and 19 D3) ≥18 years of age with baseline 25D levels <30 ng/mL were recruited from an academic ambulatory osteoporosis clinic.
  
  
  
  Serum measures were total 25D, free 25D (directly measured), 1,25-dihydroxyvitamin D, calcium, and iPTH. Urine measure was fasting calcium:creatinine ratio.
  
  
  
  Baseline total (22.2 ± 3.3 vs 23.3 ± 7.2 ng/mL; P = .5) and free (5.4 ± 0.8 vs 5.3 ± 1.7 pg/mL; P = .8) 25D levels were similar between D2 and D3 groups. Increases in total (+27.6 vs +12.2 ng/mL; P = .001) and free (+3.6 vs +6.2 pg/mL; P = .02) 25D levels were greater with D3 vs D2. Percentage change in iPTH was significantly associated with change in free (but not total) 25D, without and with adjustment for supplementation regimen, change in 1,25-dihydroxyvitamin D, and change in calcium.
  
  
  
  D3 increased total and free 25D levels to a greater extent than D2. Free 25D may be superior to total 25D as a marker of vitamin D bioactivity.
authors.affiliation: Department of Medicine, Division of Geriatrics (A.S.), and Department of Orthopaedic Surgery (R.F.C., S.W., B.M., B.R., J.S.A.), University of California, Los Angeles, Los Angeles, California 90095; David Geffen School of Medicine (C.M.), Los Angeles, California 90095; Future Diagnostics (L.S., T.H.), 6603 BN Wijchen, The Netherlands; Esoterix, Inc. (S.P., B.H.), Austin, Texas 78744; and Institute of Metabolism and Systems Research (M.H.), The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: Albert
authors.initials: A
authors.lastname: Shieh
authors.affiliation: Department of Medicine, Division of Geriatrics (A.S.), and Department of Orthopaedic Surgery (R.F.C., S.W., B.M., B.R., J.S.A.), University of California, Los Angeles, Los Angeles, California 90095; David Geffen School of Medicine (C.M.), Los Angeles, California 90095; Future Diagnostics (L.S., T.H.), 6603 BN Wijchen, The Netherlands; Esoterix, Inc. (S.P., B.H.), Austin, Texas 78744; and Institute of Metabolism and Systems Research (M.H.), The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: Rene F
authors.initials: RF
authors.lastname: Chun
authors.affiliation: Department of Medicine, Division of Geriatrics (A.S.), and Department of Orthopaedic Surgery (R.F.C., S.W., B.M., B.R., J.S.A.), University of California, Los Angeles, Los Angeles, California 90095; David Geffen School of Medicine (C.M.), Los Angeles, California 90095; Future Diagnostics (L.S., T.H.), 6603 BN Wijchen, The Netherlands; Esoterix, Inc. (S.P., B.H.), Austin, Texas 78744; and Institute of Metabolism and Systems Research (M.H.), The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: Christina
authors.initials: C
authors.lastname: Ma
authors.affiliation: Department of Medicine, Division of Geriatrics (A.S.), and Department of Orthopaedic Surgery (R.F.C., S.W., B.M., B.R., J.S.A.), University of California, Los Angeles, Los Angeles, California 90095; David Geffen School of Medicine (C.M.), Los Angeles, California 90095; Future Diagnostics (L.S., T.H.), 6603 BN Wijchen, The Netherlands; Esoterix, Inc. (S.P., B.H.), Austin, Texas 78744; and Institute of Metabolism and Systems Research (M.H.), The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: Sten
authors.initials: S
authors.lastname: Witzel
authors.affiliation: Department of Medicine, Division of Geriatrics (A.S.), and Department of Orthopaedic Surgery (R.F.C., S.W., B.M., B.R., J.S.A.), University of California, Los Angeles, Los Angeles, California 90095; David Geffen School of Medicine (C.M.), Los Angeles, California 90095; Future Diagnostics (L.S., T.H.), 6603 BN Wijchen, The Netherlands; Esoterix, Inc. (S.P., B.H.), Austin, Texas 78744; and Institute of Metabolism and Systems Research (M.H.), The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: Briana
authors.initials: B
authors.lastname: Meyer
authors.affiliation: Department of Medicine, Division of Geriatrics (A.S.), and Department of Orthopaedic Surgery (R.F.C., S.W., B.M., B.R., J.S.A.), University of California, Los Angeles, Los Angeles, California 90095; David Geffen School of Medicine (C.M.), Los Angeles, California 90095; Future Diagnostics (L.S., T.H.), 6603 BN Wijchen, The Netherlands; Esoterix, Inc. (S.P., B.H.), Austin, Texas 78744; and Institute of Metabolism and Systems Research (M.H.), The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: Brandon
authors.initials: B
authors.lastname: Rafison
authors.affiliation: Department of Medicine, Division of Geriatrics (A.S.), and Department of Orthopaedic Surgery (R.F.C., S.W., B.M., B.R., J.S.A.), University of California, Los Angeles, Los Angeles, California 90095; David Geffen School of Medicine (C.M.), Los Angeles, California 90095; Future Diagnostics (L.S., T.H.), 6603 BN Wijchen, The Netherlands; Esoterix, Inc. (S.P., B.H.), Austin, Texas 78744; and Institute of Metabolism and Systems Research (M.H.), The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: Leon
authors.initials: L
authors.lastname: Swinkels
authors.affiliation: Department of Medicine, Division of Geriatrics (A.S.), and Department of Orthopaedic Surgery (R.F.C., S.W., B.M., B.R., J.S.A.), University of California, Los Angeles, Los Angeles, California 90095; David Geffen School of Medicine (C.M.), Los Angeles, California 90095; Future Diagnostics (L.S., T.H.), 6603 BN Wijchen, The Netherlands; Esoterix, Inc. (S.P., B.H.), Austin, Texas 78744; and Institute of Metabolism and Systems Research (M.H.), The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: Tonnie
authors.initials: T
authors.lastname: Huijs
authors.affiliation: Department of Medicine, Division of Geriatrics (A.S.), and Department of Orthopaedic Surgery (R.F.C., S.W., B.M., B.R., J.S.A.), University of California, Los Angeles, Los Angeles, California 90095; David Geffen School of Medicine (C.M.), Los Angeles, California 90095; Future Diagnostics (L.S., T.H.), 6603 BN Wijchen, The Netherlands; Esoterix, Inc. (S.P., B.H.), Austin, Texas 78744; and Institute of Metabolism and Systems Research (M.H.), The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: Sam
authors.initials: S
authors.lastname: Pepkowitz
authors.affiliation: Department of Medicine, Division of Geriatrics (A.S.), and Department of Orthopaedic Surgery (R.F.C., S.W., B.M., B.R., J.S.A.), University of California, Los Angeles, Los Angeles, California 90095; David Geffen School of Medicine (C.M.), Los Angeles, California 90095; Future Diagnostics (L.S., T.H.), 6603 BN Wijchen, The Netherlands; Esoterix, Inc. (S.P., B.H.), Austin, Texas 78744; and Institute of Metabolism and Systems Research (M.H.), The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: Brett
authors.initials: B
authors.lastname: Holmquist
authors.affiliation: Department of Medicine, Division of Geriatrics (A.S.), and Department of Orthopaedic Surgery (R.F.C., S.W., B.M., B.R., J.S.A.), University of California, Los Angeles, Los Angeles, California 90095; David Geffen School of Medicine (C.M.), Los Angeles, California 90095; Future Diagnostics (L.S., T.H.), 6603 BN Wijchen, The Netherlands; Esoterix, Inc. (S.P., B.H.), Austin, Texas 78744; and Institute of Metabolism and Systems Research (M.H.), The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: Martin
authors.initials: M
authors.lastname: Hewison
authors.affiliation: Department of Medicine, Division of Geriatrics (A.S.), and Department of Orthopaedic Surgery (R.F.C., S.W., B.M., B.R., J.S.A.), University of California, Los Angeles, Los Angeles, California 90095; David Geffen School of Medicine (C.M.), Los Angeles, California 90095; Future Diagnostics (L.S., T.H.), 6603 BN Wijchen, The Netherlands; Esoterix, Inc. (S.P., B.H.), Austin, Texas 78744; and Institute of Metabolism and Systems Research (M.H.), The University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
authors.forename: John S
authors.initials: JS
authors.lastname: Adams
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood; D002118:Calcium / Q000097:blood*; D016022:Case-Control Studies; D002762:Cholecalciferol / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D004872:Ergocalciferols / Q000008:administration & dosage*; D006706:Homeostasis / Q000187:drug effects; D020249:Hormone Replacement Therapy; D006801:Humans; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D014808:Vitamin D Deficiency / Q000097:blood* / Q000188:drug therapy*
chemical_list: D015415:Biomarkers; D004872:Ergocalciferols; D010281:Parathyroid Hormone; D014807:Vitamin D; D002762:Cholecalciferol; C104450:25-hydroxyvitamin D; D002118:Calcium