title: Predictors of vitamin D status in predialysis chronic kidney disease patients: a cross-sectional analysis in a high ultraviolet climate.
abstract: OBJECTIVE
  To determine vitamin D status in a subtropical climate among an unselected, referred predialysis chronic kidney disease (CKD) population; assess risks and correlates; and review whether higher 25-hydroxyvitamin D (25-OHD) concentration can mitigate the decrement in circulating 1,25-dihydroxyvitamin D (1,25-OHD) normally encountered with advancing CKD.
  
  
  METHODS
  Prospective cross-sectional cohort study.
  
  
  METHODS
  Renal unit in Brisbane, Australia (27°28' S).
  
  
  METHODS
  Five hundred ninety-three consecutive CKD patients (stage 1 to 5).
  
  
  METHODS
  25-OHD insufficiency (concentrations: 15 to 30 ng/mL) and deficiency (<15 ng/mL), bone-mineral parameters, including 1,25-OHD, calcium, and phosphate.
  
  
  RESULTS
  Despite potentially higher environmental ultraviolet (UV) exposure, only 48% of patients with CKD were 25-OHD sufficient. Traditional risks for hypovitaminosis D were maintained, and sufficiency was independently predicted by testing in the summer/autumn period (odds ratio [OR]: 2.77, 95% confidence interval [CI]: 1.88 to 4.08, P < .001), male gender (OR: 2.18, 95%CI: 1.46 to 3.24, P < .001), Caucasian race (OR: 2.28, 95%CI: 1.37 to 3.78, P = .001), hypoalbuminemia (OR: 0.47, 95%CI: 0.25 to 0.85, P = .01), macroalbuminuria (OR: 0.60, 95%CI: 0.39 to 0.92, P = .02), and normal body mass index (OR: 1.94, 95%CI: 1.22 to 3.07, P = .005). Vitamin D sufficiency was also associated with higher corrected calcium (0.4 mg/dL increments; OR: 1.29, 95%CI: 1.08 to 1.55, P = .005). Although circulating 25-OHD concentrations were relatively maintained across the range of renal function observed, 1,25-OHD concentrations decreased with advancing CKD.
  
  
  CONCLUSIONS
  25-OHD insufficiency is mitigated but still highly prevalent in patients with CKD in a high ambient UV environment. Despite the maintenance of relatively higher 25-OHD concentrations with advancing CKD, substrate availability does not appear to be a major determinant of circulating 1,25-OHD.
authors.affiliation: Department of Nephrology, Princess Alexandra Hospital, Brisbane, Australia. william_petchey@health.qld.gov.au
authors.forename: William G
authors.initials: WG
authors.lastname: Petchey
authors.forename: David W
authors.initials: DW
authors.lastname: Johnson
authors.forename: Carmel M
authors.initials: CM
authors.lastname: Hawley
authors.forename: Nicole M
authors.initials: NM
authors.lastname: Isbel
mesh_terms: D000328:Adult; D000368:Aged; D015519:Bone Density; D002118:Calcium / Q000097:blood; D002980:Climate; D003430:Cross-Sectional Studies; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D007668:Kidney / Q000187:drug effects / Q000503:physiopathology; D007676:Kidney Failure, Chronic / Q000503:physiopathology; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009752:Nutritional Status; D010281:Parathyroid Hormone / Q000097:blood; D010710:Phosphates / Q000097:blood; D015995:Prevalence; D011446:Prospective Studies; D012621:Seasons; D011795:Surveys and Questionnaires; D014807:Vitamin D / Q000008:administration & dosage* / Q000097:blood*; D014808:Vitamin D Deficiency / Q000453:epidemiology* / Q000503:physiopathology; D014815:Vitamins / Q000008:administration & dosage* / Q000097:blood*
chemical_list: D010281:Parathyroid Hormone; D010710:Phosphates; D014815:Vitamins; D014807:Vitamin D; D002118:Calcium