title: Acute fasting diminishes the circadian rhythm of biochemical markers of bone resorption.
abstract: OBJECTIVE
  Biochemical markers of bone turnover exhibit circadian rhythms with the peak during the night/early morning and the nadir in the late afternoon. The nocturnal increase in bone resorption could theoretically be caused by the absence of food consumption which brings about a decrease in net calcium absorption and an increase in parathyroid hormone (PTH), followed by increased bone resorption in response to the body's demand for calcium. The aim of the present study was to assess the influence of a 33-h fast on the circadian variation in biochemical markers of bone turnover.
  
  
  METHODS
  Eleven healthy premenopausal women (age: 24+/-5 years) participated in a randomised, cross-over study consisting of two periods: either 33h of fasting (fasting) followed 1 week later by a 33-h period with regular meals eaten at 0800-0830h, 1130-1230h and 1800-1900h (control) or vice versa.
  
  
  METHODS
  Urinary CrossLaps (U-CL/Cr) corrected with creatinine, as a marker of bone resorption; serum osteocalcin (sOC) as a marker of bone formation; serum intact PTH (iPTH); serum phosphate; and serum calcium corrected with albumin.
  
  
  RESULTS
  Both the fasting and the control periods showed a significant circadian rhythm in U-CL/Cr (P<0.001), but the decrease was significantly less pronounced in the morning hours during the fasting period. Fasting resulted in a significant decrease in serum iPTH (throughout the study period) as compared with the control period (P<0.05-0.001). No change was observed in sOC by fasting.
  
  
  CONCLUSIONS
  Food consumption has a small influence on the circadian variation in bone resorption, independent of PTH. The fall in iPTH during fasting may be secondary to an increased bone resorption produced by fasting.
authors: Center for Clinical and Basic Research, Ballerup Byvej 222, DK-2750 Ballerup, Denmark.
authors: A
authors: A
authors: Schlemmer
authors: C
authors: C
authors: Hassager
mesh_terms: D000328:Adult; D015415:Biomarkers; D001862:Bone Resorption / Q000378:metabolism*; D002118:Calcium / Q000097:blood; D002940:Circadian Rhythm; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004797:Enzyme-Linked Immunosorbent Assay; D005215:Fasting / Q000378:metabolism*; D005260:Female; D006801:Humans; D015675:Osteocalcin / Q000097:blood / Q000652:urine; D010281:Parathyroid Hormone / Q000097:blood / Q000652:urine; D010710:Phosphates / Q000097:blood / Q000652:urine
chemical_list: D015415:Biomarkers; D010281:Parathyroid Hormone; D010710:Phosphates; D015675:Osteocalcin; D002118:Calcium