title: Vitamin D levels, bone turnover and bone mineral density show seasonal variation in patients with chronic kidney disease stage 5.
abstract: OBJECTIVE
  Many patients with chronic kidney disease (CKD) have reduced levels of 25-hydroxyvitamin D (25(OH)D). Although renal conversion of 25(OH)D to calcitriol is reduced or absent in CKD stage 5 (GFR < 15 mL/min per 1.73 m(2) or on dialysis), 25(OH)D may have direct skeletal and non-skeletal paracrine actions. The aim of this study was to assess seasonal variation in levels of 25(OH)D, bone turnover markers and bone mineral density, which would support a direct physiological role for 25(OH)D.
  
  
  METHODS
  Vitamin D levels, bone turnover markers and bone mineral density were measured and assessed for seasonal variation in 257 patients about to undergo kidney or kidney pancreas transplantation.
  
  
  RESULTS
  The mean age was 43 +/- 11 years; 62% were on haemodialysis, 24% on peritoneal dialysis and 34% had type 1 diabetes. Serum 25(OH)D was less than 50 nmol/L in 39% and lower levels were associated with female sex, diabetes and peritoneal dialysis (P < 0.0001 for each). Levels of 25(OH)D varied by season (P = 0.018; anova) peaking in autumn with a nadir in spring and calcitriol levels followed a similar seasonal trend. Bone mineral denisty Z-scores differed between summer and winter at the lumbar spine (P = 0.009) with a similar trend at the hip. Osteocalcin levels also showed seasonal periodicity (P = 0.0142) and together with alkaline phosphatase were higher in summer than winter.
  
  
  CONCLUSIONS
  In summary, these data suggest direct effects of 25(OH)D on bone parameters in CKD stage 5 and support the need for prospective studies to establish the effect of treatments that increase 25(OH)D levels in all stages of CKD.
authors.affiliation: Centre for Transplant and Renal Research, Westmead Millennium Institute, Sydney, New South Wales, Australia. g.elder@garvan.unsw.edu.au
authors.forename: Grahame J
authors.initials: GJ
authors.lastname: Elder
mesh_terms: D000328:Adult; D015519:Bone Density; D001842:Bone and Bones / Q000378:metabolism*; D005260:Female; D006801:Humans; D007676:Kidney Failure, Chronic / Q000378:metabolism* / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D012621:Seasons; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000032:analysis
chemical_list: D014807:Vitamin D; C104450:25-hydroxyvitamin D