title: Short-term high dietary calcium intake during bedrest has no effect on markers of bone turnover in healthy men.
abstract: OBJECTIVE
  Immobilization and space flight are causes of disuse osteoporosis. Increasing calcium intake may counteract this disuse-induced bone loss.
  
  
  METHODS
  We conducted two bedrest experiments (crossover design: bedrest versus ambulatory control) in a metabolic ward, studying the effect of 1000 mg/d of calcium intake (study A, length of intervention 14 d) compared with that of a high calcium intake of 2000 mg/d (study B, 6 d) on markers of bone turnover. Both studies were randomized, controlled studies with the subjects staying under well-controlled environmental conditions (study A, 9 male subjects, age 23.6+/-3.0 y; study B, 8 male subjects, age 25.5+/-2.9 y). Blood was drawn to analyze serum calcium, parathyroid hormone, procollagen type I C-terminal propeptide, and bone alkaline phosphatase. Urine (24-h) was collected for analysis of calcium, C-terminal telopeptide of collagen type I, and N-terminal telopeptide of collagen type I.
  
  
  RESULTS
  In both studies, serum calcium levels remained unchanged. Procollagen type I C-terminal propeptide was lower (P=0.03) in the bedrest phase than in the ambulatory phase in study A and tended to be lower (P=0.08) in bedrest in study B, whereas bone alkaline phosphatase was not affected in either study. Urinary calcium excretion was greater during bedrest than during the ambulatory phase (study A, P=0.005; study B, P=0.002). C-terminal telopeptide of collagen type I excretion was also greater during bedrest in both studies (study A, P<0.001; study B, P<0.001).
  
  
  CONCLUSIONS
  Doubling calcium intake to 2000 mg/d does not prevent increased bone resorption induced by bedrest.
authors.affiliation: Deutsches Zentrum fuer Luft und Raumfahrt, Institute of Aerospace Medicine, Linder Hoehe, Cologne, Germany. natalie.baecker@dlr.de
authors.forename: Natalie
authors.initials: N
authors.lastname: Baecker
authors.forename: Petra
authors.initials: P
authors.lastname: Frings-Meuthen
authors.forename: Scott M
authors.initials: SM
authors.lastname: Smith
authors.forename: Martina
authors.initials: M
authors.lastname: Heer
mesh_terms: D000328:Adult; D000469:Alkaline Phosphatase / Q000097:blood; D001510:Bed Rest; D016723:Bone Remodeling / Q000187:drug effects*; D001842:Bone and Bones / Q000201:enzymology; D002118:Calcium / Q000097:blood / Q000652:urine; D002136:Calcium, Dietary / Q000008:administration & dosage*; D024042:Collagen Type I / Q000652:urine; D018592:Cross-Over Studies; D006801:Humans; D008297:Male; D010281:Parathyroid Hormone / Q000097:blood; D010446:Peptide Fragments / Q000097:blood / Q000652:urine; D010455:Peptides / Q000652:urine; D011347:Procollagen / Q000097:blood / Q000652:urine
chemical_list: D002136:Calcium, Dietary; D024042:Collagen Type I; D010281:Parathyroid Hormone; D010446:Peptide Fragments; D010455:Peptides; D011347:Procollagen; C052929:collagen type I trimeric cross-linked peptide; C042813:procollagen type I carboxy terminal peptide; D000469:Alkaline Phosphatase; D002118:Calcium