title: Bioavailability of vitamin D(2) and D(3) in healthy volunteers, a randomized placebo-controlled trial.
abstract: BACKGROUND
  The bioequivalence of the different forms of vitamin D, ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3), has been questioned. Earlier studies have suggested that vitamin D2 is less biologically active than vitamin D3.
  
  
  OBJECTIVE
  In a parallel study, we tested the effects of supplementation with 50-μg/d doses of vitamin D2 or D3 or a placebo over a period of 8 weeks on 25(OH)D2, 25(OH)D3, their sum 25(OH)D (primary outcome variables), and PTH in healthy volunteers applying a double-blind, randomized study design. The study was conducted during the winter of 2012 in Halle (Saale), Germany, at latitude 51°47N, when UVB irradiation is virtually absent. Blood samples for the determinations of vitamin D status and PTH were collected at baseline and after 4 and 8 weeks of supplementation.
  
  
  RESULTS
  In the placebo group (n = 19), 25(OH)D3 decreased from 39.4 ± 14.2 to 31.1 ± 12.4 nmol/L after 8 weeks (P < .01). In the vitamin D3 group (n = 42), the concentrations of 25(OH)D3 increased from 41.5 ± 22.8 nmol/L at baseline to 88.0 ± 22.1 nmol/L after 8 weeks (P < .01). In the group receiving vitamin D2 (n = 46), the 25(OH)D2 concentrations increased significantly, whereas the 25(OH)D3 concentration fell from 36.4 ± 13.3 nmol/L at baseline to 16.6 ± 6.3 nmol/L after 8 weeks (P < .01). The total 25(OH)D was not different between the groups at baseline but differed significantly between the groups after 4 and 8 weeks (P < .001).
  
  
  CONCLUSIONS
  Vitamin D3 increases the total 25(OH)D concentration more than vitamin D2. Vitamin D2 supplementation was associated with a decrease in 25(OH)D3, which can explain the different effect on total 25(OH)D.
authors.affiliation: PhD, Department of Clinical Medicine, P.O. Box 7804, N-5020 Bergen, Norway. jutta.dierkes@med.uib.no.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Lehmann
authors.forename: Frank
authors.initials: F
authors.lastname: Hirche
authors.forename: Gabriele I
authors.initials: GI
authors.lastname: Stangl
authors.forename: Katja
authors.initials: K
authors.lastname: Hinz
authors.forename: Sabine
authors.initials: S
authors.lastname: Westphal
authors.forename: Jutta
authors.initials: J
authors.lastname: Dierkes
mesh_terms: D015652:25-Hydroxyvitamin D 2 / Q000097:blood; D000328:Adult; D000368:Aged; D001682:Biological Availability; D002112:Calcifediol / Q000097:blood; D002762:Cholecalciferol / Q000008:administration & dosage / Q000097:blood* / Q000493:pharmacokinetics*; D004872:Ergocalciferols / Q000008:administration & dosage / Q000097:blood* / Q000493:pharmacokinetics*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008875:Middle Aged; D010919:Placebos; D014815:Vitamins / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics; D055815:Young Adult
chemical_list: D004872:Ergocalciferols; D010919:Placebos; D014815:Vitamins; D002762:Cholecalciferol; D015652:25-Hydroxyvitamin D 2; D002112:Calcifediol