title: Calcium supplementation and parathyroid hormone response to vigorous walking in postmenopausal women.
abstract: BACKGROUND
  Disruptions in calcium (Ca) homeostasis during exercise may influence skeletal adaptations to exercise training. In young men, vigorous cycling causes increases in parathyroid hormone (PTH) and bone resorption (C-terminal telopeptides of type I collagen [CTX]); responses are attenuated by Ca supplementation. The study aimed to determine whether vigorous walking causes similar increases in PTH and CTX in older women and how the timing of Ca supplementation before and during exercise influences these responses.
  
  
  METHODS
  In experiment 1, 10 women (61 ± 4 yr) consumed 125 mL of either a Ca-fortified (1 g·L) or control beverage every 15 min during exercise starting 60 min before and continuing during 60 min of exercise. In experiment 2, 23 women (61 ± 4 yr) consumed 200 mL of a Ca-fortified (1 g·L) or control beverage every 15 min starting 15 min before and continuing during 60 min of exercise. The exercise was treadmill walking at 75%-80% V˙O2peak.
  
  
  RESULTS
  In experiment 1, serum ionized Ca decreased in the control condition (P < 0.001), but not with Ca supplementation. PTH increased after exercise on both days (Ca, P = 0.05; control, P = 0.009) but was attenuated by Ca supplementation (8.3 vs 26.1 pg·mL; P = 0.03). CTX increased only on the control day (P = 0.02). In experiment 2, serum ionized Ca decreased on Ca and control days (Ca and control, P < 0.001), but less so on the Ca day (P = 0.04). PTH (Ca and control, P < 0.001) and CTX (Ca, P = 0.02; control P = 0.007) increased on the Ca and control day, and there were no differences in the changes.
  
  
  CONCLUSIONS
  The timing of Ca supplementation may be a key mediator of Ca homeostasis during acute exercise. Further research is necessary to determine how this influences skeletal adaptations to training.
authors.affiliation: 1Division of Geriatric Medicine, School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO; 2Division of General Internal Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO; and 3Department of Preventative Medicine and Biostatistics, University of Colorado Anschutz Medical Campus, Aurora, CO.
authors.forename: Karen L
authors.initials: KL
authors.lastname: Shea
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Barry
authors.forename: Vanessa D
authors.initials: VD
authors.lastname: Sherk
authors.forename: Kent C
authors.initials: KC
authors.lastname: Hansen
authors.forename: Pamela
authors.initials: P
authors.lastname: Wolfe
authors.forename: Wendy M
authors.initials: WM
authors.lastname: Kohrt
mesh_terms: D000368:Aged; D001862:Bone Resorption; D002136:Calcium, Dietary / Q000008:administration & dosage / Q000494:pharmacology*; D024042:Collagen Type I / Q000097:blood; D018592:Cross-Over Studies; D019587:Dietary Supplements; D004311:Double-Blind Method; D005260:Female; D006706:Homeostasis; D006801:Humans; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood*; D010455:Peptides / Q000097:blood; D017698:Postmenopause / Q000097:blood*; D016138:Walking / Q000502:physiology*
chemical_list: D002136:Calcium, Dietary; D024042:Collagen Type I; D010281:Parathyroid Hormone; D010455:Peptides; C052929:collagen type I trimeric cross-linked peptide