title: Vitamin D status and bone and connective tissue turnover in brown bears (Ursus arctos) during hibernation and the active state.
abstract: BACKGROUND
  Extended physical inactivity causes disuse osteoporosis in humans. In contrast, brown bears (Ursus arctos) are highly immobilised for half of the year during hibernation without signs of bone loss and therefore may serve as a model for prevention of osteoporosis.
  
  
  OBJECTIVE
  To study 25-hydroxy-vitamin D (25OHD) levels and bone turnover markers in brown bears during the hibernating state in winter and during the active state in summer. We measured vitamin D subtypes (D₂ and D₃), calcitropic hormones (parathyroid hormone [PTH], 1,25-dihydroxy-vitamin D [1,25(OH)₂D]) and bone turnover parameters (osteocalcin, ICTP, CTX-I), PTH, serum calcium and PIIINP.
  
  
  METHODS
  We drew blood from seven immobilised wild brown bears during hibernation in February and in the same bears while active in June.
  
  
  RESULTS
  Serum 25-hydroxy-cholecalciferol (25OHD₃) was significantly higher in the summer than in the winter (22.8±4.6 vs. 8.8±2.1 nmol/l, two tailed p-2p = 0.02), whereas 25-hydroxy-ergocalciferol (25OHD₂) was higher in winter (54.2±8.3 vs. 18.7±1.7 nmol/l, 2p<0.01). Total serum calcium and PTH levels did not differ between winter and summer. Activated 1,25(OH)₂D demonstrated a statistically insignificant trend towards higher summer levels. Osteocalcin levels were higher in summer than winter, whereas other markers of bone turnover (ICTP and CTX-I) were unchanged. Serum PIIINP, which is a marker of connective tissue and to some degree muscle turnover, was significantly higher during summer than during winter.
  
  
  CONCLUSIONS
  Dramatic changes were documented in the vitamin D₃/D₂ ratio and in markers of bone and connective tissue turnover in brown bears between hibernation and the active state. Because hibernating brown bears do not develop disuse osteoporosis, despite extensive physical inactivity we suggest that they may serve as a model for the prevention of this disease.
authors: The Osteoporosis Clinic, Aarhus University Hospital, Aarhus, Denmark. p-vest@post4 tele.dk
authors: Peter
authors: P
authors: Vestergaard
authors: Ole-Gunnar
authors: OG
authors: Støen
authors: Jon E
authors: JE
authors: Swenson
authors: Leif
authors: L
authors: Mosekilde
authors: Lene
authors: L
authors: Heickendorff
authors: Ole
authors: O
authors: Fröbert
mesh_terms: D000818:Animals; D016723:Bone Remodeling / Q000502:physiology*; D001842:Bone and Bones / Q000378:metabolism*; D003238:Connective Tissue / Q000378:metabolism; D005260:Female; D006605:Hibernation / Q000502:physiology*; D008297:Male; D012621:Seasons; D013548:Sweden; D001503:Ursidae / Q000097:blood* / Q000502:physiology*; D014807:Vitamin D / Q000097:blood*
chemical_list: D014807:Vitamin D