title: Acute calcium ingestion attenuates exercise-induced disruption of calcium homeostasis.
abstract: OBJECTIVE
  Exercise is associated with a decrease in bone mineral density under certain conditions. One potential mechanism is increased bone resorption due to an exercise-induced increase in parathyroid hormone (PTH), possibly triggered by dermal calcium loss. The purpose of this investigation was to determine whether calcium supplementation either before or during exercise attenuates exercise-induced increases in PTH and C-terminal telopeptide of Type I collagen (CTX; a marker of bone resorption).
  
  
  METHODS
  Male endurance athletes (n = 20) completed three 35-km cycling time trials under differing calcium supplementation conditions: 1) 1000 mg of calcium 20 min before exercise and placebo during, 2) placebo before and 250 mg of calcium every 15 min during exercise (1000 mg total), or 3) placebo before and during exercise. Calcium was delivered in a 1000-mg·L(-1) solution. Supplementation was double-blinded, and trials were performed in random order. PTH, CTX, bone-specific alkaline phosphatase (BAP; a marker of bone formation), and ionized calcium (iCa) were measured before and immediately after exercise.
  
  
  RESULTS
  CTX increased and iCa decreased similarly in response to exercise under all test conditions. When compared with placebo, calcium supplementation before exercise attenuated the increase in PTH (mean ± SE: 55.8 ± 15.0 vs 74.0 ± 14.2 pg·mL(-1), P = 0.04); there was a similar trend (58.0 ± 17.4, P = 0.07) for calcium supplementation during exercise. There were no effects of calcium on changes in CTX, BAP, and iCa.
  
  
  CONCLUSIONS
  Calcium supplementation before exercise attenuated the disruption of PTH. Further research is needed to determine the effects of repeated increases in PTH and CTX on bone (i.e., exercise training) and whether calcium supplementation can diminish any exercise-induced demineralization.
authors.affiliation: Department of Medicine, Division of General Internal Medicine, University of Colorado, Anschutz Medical Campus, Aurora, CO, USA. daniel.barry@ucdenver.edu
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Barry
authors.forename: Kent C
authors.initials: KC
authors.lastname: Hansen
authors.forename: Rachael E
authors.initials: RE
authors.lastname: van Pelt
authors.forename: Michael
authors.initials: M
authors.lastname: Witten
authors.forename: Pamela
authors.initials: P
authors.lastname: Wolfe
authors.forename: Wendy M
authors.initials: WM
authors.lastname: Kohrt
mesh_terms: D000328:Adult; D001642:Bicycling; D002136:Calcium, Dietary / Q000008:administration & dosage* / Q000494:pharmacology; D004311:Double-Blind Method; D015444:Exercise / Q000502:physiology*; D006706:Homeostasis / Q000187:drug effects*; D006801:Humans; D008297:Male; D010281:Parathyroid Hormone / Q000378:metabolism*; D013542:Sweat / Q000737:chemistry
chemical_list: D002136:Calcium, Dietary; D010281:Parathyroid Hormone
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