title: Seasonal changes in vitamin D status and bone turnover in healthy Irish postmenopausal women.
abstract: OBJECTIVE
  To examine the effect of season on biochemical markers of bone turnover in 51-to 75-year-old Irish women and to investigate whether such changes are related to vitamin D status.
  
  
  METHODS
  Longitudinal observational study.
  
  
  METHODS
  Cork, Ireland (52 degrees N).
  
  
  METHODS
  76 apparently healthy, free-living postmenopausal women (aged 51-75 years), not taking any medication and free from any condition likely to affect vitamin D status or calcium/bone metabolism.
  
  
  RESULTS
  Serum 25-hydroxyvitamin D [S-25(OH)D] showed a clear seasonal variation with significantly higher (p < 0.001) values during late summer than late winter. Both urinary pyridinoline (Ur-Pyr) (p < 0.01) and deoxypyridinoline (Ur-Dpyr) (p < 0.001), but not serum parathyroid hormone or osteocalcin, showed a marked seasonal variation with lowest values during late-summer. Stratifying women into those with S-25(OH)D levels > or = or <50 nmol/L (vitamin D adequate and inadequate, respectively) during late-winter, showed that Ur-Pyr and Ur-Dpyr in both groups were significantly (p < 0.05) lower during late summer, and the magnitude of the reduction from winter to summer was similar in both groups.
  
  
  CONCLUSIONS
  Seasonal changes in bone resorption markers appeared to be linked to seasonal changes in vitamin D status. Further research is needed to investigate the impact of these changes on risk of bone loss and fracture.
authors.affiliation: Department of Food and Nutritional Sciences, University College, Cork, Ireland. t.hill@ucc.ie
authors.forename: Tom R
authors.initials: TR
authors.lastname: Hill
authors.forename: David
authors.initials: D
authors.lastname: McCarthy
authors.forename: Jette
authors.initials: J
authors.lastname: Jakobsen
authors.forename: Christel
authors.initials: C
authors.lastname: Lamberg-Allardt
authors.forename: Mairead
authors.initials: M
authors.lastname: Kiely
authors.forename: Kevin D
authors.initials: KD
authors.lastname: Cashman
mesh_terms: D000368:Aged; D000596:Amino Acids / Q000652:urine; D015415:Biomarkers / Q000097:blood / Q000652:urine; D001862:Bone Resorption / Q000453:epidemiology / Q000652:urine; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007494:Ireland / Q000453:epidemiology; D008137:Longitudinal Studies; D008875:Middle Aged; D009752:Nutritional Status; D015675:Osteocalcin / Q000097:blood; D015663:Osteoporosis, Postmenopausal / Q000097:blood / Q000453:epidemiology* / Q000652:urine; D017698:Postmenopause; D012016:Reference Values; D012621:Seasons; D014807:Vitamin D / Q000097:blood*; D014808:Vitamin D Deficiency / Q000097:blood / Q000453:epidemiology*
chemical_list: D000596:Amino Acids; D015415:Biomarkers; D015675:Osteocalcin; D014807:Vitamin D; C015484:pyridinoline; C036020:deoxypyridinoline