title: Effects of elevated carbon dioxide environment on calcium metabolism in humans.
abstract: BACKGROUND
  Chronic respiratory acidosis induced by an elevated carbon dioxide (CO2) environment should provoke hypercalciuria with related total body and subsequent bone calcium losses. We examined this hypothesis in four healthy male volunteers, who were exposed during a 25-d period to an 0.7% CO2 environment within a deep diving isolation chamber. Three months later the same subjects were reexamined during a second campaign being exposed to a 1.2% CO2 atmosphere.
  
  
  METHODS
  The subjects received a constant calcium intake (1.4 g.d-1) and vitamin D supplement (1000 IU.d-1) during both campaigns. Calcium balance (oral calcium intake minus urinary and fecal calcium output) was evaluated. Serum calcium concentrations and biomarkers of bone metabolism were measured, in order to evaluate bone turnover. Additionally, the response to an acute oral calcium load was examined as a sensitive measure of changes in calcium metabolism.
  
  
  RESULTS
  Both, urinary calcium excretion (from 245 +/- 38 to 199 +/- 31 mg.d-1; mean +/- SE, 0.7% and 1.2%, respectively) and fecal calcium losses (from 1229 +/- 128 to 996 +/- 62 mg.d-1) were significantly reduced in the higher (1.2%) CO2 atmosphere. Although more calcium was retained in the body during the 1.2% than during the 0.7% CO2 campaign, serum calcium concentrations and biomarkers of bone formation were significantly lower in the higher CO2 campaign. Furthermore, bone resorption was slightly increased in the 1.2% experiment.
  
  
  CONCLUSIONS
  Elevated CO2 atmosphere may dose-dependently preserve body calcium without a parallel improvement of bone substance.
authors.affiliation: Institut für Luft- und Raumfahrtmedizin der Deutschen Forschungsanstalt für Luft- und Raumfahrt (DLR), Cologne, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Drummer
authors.forename: V
authors.initials: V
authors.lastname: Friedel
authors.forename: A
authors.initials: A
authors.lastname: Börger
authors.forename: I
authors.initials: I
authors.lastname: Störmer
authors.forename: S
authors.initials: S
authors.lastname: Wolter
authors.forename: A
authors.initials: A
authors.lastname: Zittermann
authors.forename: G
authors.initials: G
authors.lastname: Wolfram
authors.forename: M
authors.initials: M
authors.lastname: Heer
mesh_terms: D000142:Acidosis, Respiratory / Q000139:chemically induced / Q000150:complications*; D000328:Adult; D016902:Air Pollution, Indoor / Q000009:adverse effects*; D016723:Bone Remodeling / Q000187:drug effects / Q000502:physiology*; D002245:Carbon Dioxide / Q000009:adverse effects*; D002908:Chronic Disease; D018504:Ecological Systems, Closed; D006801:Humans; D006935:Hypercapnia / Q000139:chemically induced / Q000150:complications*; D006996:Hypocalcemia / Q000097:blood* / Q000139:chemically induced / Q000652:urine*; D008297:Male; D018561:Space Simulation
chemical_list: D002245:Carbon Dioxide