title: Plasma 1,25(OH)2D levels decrease in postmenopausal women with hypovitaminosis D.
abstract: OBJECTIVE
  Although calcitriol (1,25(OH)2D) is considered the biologically active vitamin D metabolite, several studies have shown that calcidiol (25OHD) is the vitamin D metabolite that is most closely linked to parathyroid function and indices of calcium homeostasis. Moreover, low levels of 25OHD have been associated with increased risk of different diseases including cancer, diabetes, and myopathy.
  
  
  METHODS
  Cross-sectional study.
  
  
  METHODS
  We studied relations between plasma concentrations of 25OHD, 1,25(OH)2D, and parathyroid hormone (PTH) in fasting plasma samples from 315 healthy postmenopausal women randomly selected from the local background population.
  
  
  RESULTS
  P-1,25(OH)2D levels varied in a concentration-dependent manner with P-25OHD levels (P<0.001). Thus, P-1,25(OH)2D levels were the lowest in women with vitamin D insufficiency, i.e., P-1,25(OH)2D levels were reduced by approximately one-third in subjects with P-25OHD levels below 25 nmol/l compared with levels above 80 nmol/l (P<0.01). The association was most pronounced at P-25OHD concentrations below 80 nmol/l, whereas no major increase in P-1,25(OH)2D was observed at P-25OHD concentrations above 80 nmol/l. In multiple regression analysis, PTH was a minor although significant predictor of P-1,25(OH)2D levels.
  
  
  CONCLUSIONS
  In normal postmenopausal women, the conversion of 25OHD to active vitamin D depends on the substrate concentration. Our data support that vitamin D insufficiency should be considered at P-25OHD levels below 80 nmol/l.
authors: Department of Endocrinology, Aarhus University Hospital, Aarhus Sygehus, Tage-Hansens Gade 2, DK-8000 Aarhus, Denmark. rejnmark@post6.tele.dk
authors: Lars
authors: L
authors: Rejnmark
authors: Peter
authors: P
authors: Vestergaard
authors: Lene
authors: L
authors: Heickendorff
authors: Leif
authors: L
authors: Mosekilde
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002117:Calcitriol / Q000097:blood*; D002118:Calcium / Q000097:blood; D003404:Creatinine / Q000097:blood; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008875:Middle Aged; D009994:Osmolar Concentration; D010281:Parathyroid Hormone / Q000097:blood; D010710:Phosphates / Q000097:blood; D017698:Postmenopause / Q000097:blood*; D014808:Vitamin D Deficiency / Q000097:blood* / Q000145:classification
chemical_list: D010281:Parathyroid Hormone; D010710:Phosphates; D003404:Creatinine; D002117:Calcitriol; D002118:Calcium