title: Seasonal and age-related differences in serum 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D and parathyroid hormone in patients from Western Norway.
abstract: OBJECTIVE
  The aim of this study was to investigate the seasonal and age-related variation of vitamin D and PTH serum concentrations in a large general patient population in Western Norway.
  
  
  METHODS
  A retrospective study was conducted at the Hormone laboratory, Haukeland University Hospital, Bergen, Norway. All analyses of 25-hydroxyvitamin D (25(OH)D) (n = 8325), 1,25-dihydroxyvitamin D (1,25(OH)2D) (n = 4509) and PTH (n = 4203) requested from private practitioners from 2005 to 2008 were included. All three analytes were available in 1551 subjects. Subjects. Mean age of the study population was 49.8 years and 70.9% of the samples were from women.
  
  
  RESULTS
  The highest concentrations of 25(OH)D and 1,25(OH)2D were observed in July-September. In April 43% of the studied population had 25(OH)D concentrations below 50 nmol/L. There was a positive correlation between 25(OH)D and 1,25(OH)2D (p < 0.001). The levels of 25(OH)D and PTH were negatively correlated (p < 0.001) while 1,25(OH)2D and PTH showed a weak positive correlation (p = 0.015). We observed higher concentrations of 25(OH)D (p = 0.003) and lower 1,25(OH)2D levels (p < 0.001) in the older age groups. PTH increased throughout the whole age span (p < 0.001).
  
  
  CONCLUSIONS
  We observed a seasonal variation in 25(OH)D and 1,25(OH)2D with low serum concentrations during winter/early spring while PTH showed an inverse pattern. Higher levels of PTH in winter and the elderly may reflect an impaired vitamin D status that may affect calcium homeostasis and bone health.
authors.affiliation: The Hormone Laboratory, Haukeland University Hospital, 5021 Bergen, Norway. monika.christensen@med.uib.no
authors.forename: Monika H E
authors.initials: MH
authors.lastname: Christensen
authors.forename: Ernst A
authors.initials: EA
authors.lastname: Lien
authors.forename: Steinar
authors.initials: S
authors.lastname: Hustad
authors.forename: Bjørg
authors.initials: B
authors.lastname: Almås
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D010281:Parathyroid Hormone / Q000097:blood*; D012189:Retrospective Studies; D012621:Seasons; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood; D055815:Young Adult
chemical_list: D010281:Parathyroid Hormone; D014807:Vitamin D; C097949:1,25-dihydroxyvitamin D; C104450:25-hydroxyvitamin D