title: A novel dual radio- and stable-isotope method for measuring calcium absorption in humans: comparison with the whole-body radioisotope retention method.
abstract: BACKGROUND
  Dietary calcium absorption can be determined only with the use of isotope techniques. Currently used isotope techniques require exclusive equipment or are not true tracer approaches.
  
  
  OBJECTIVE
  The objective was to compare a dual-isotope method combining radioisotopes and stable isotopes with a whole-body radioisotope retention method for measuring calcium absorption.
  
  
  METHODS
  Seven healthy adults aged 21-27 y consumed a test meal containing 63 +/- 14 (macro x +/- SD) mg Ca together with a water solution of (47)Ca (0.11 MBq). One hour after ingestion, 18 mg (44)Ca was administered intravenously. All feces and urine were collected for 5 and 6 d, respectively. Calcium absorption was estimated from whole-body retention of the radioisotope 12 times over 3 wk after ingestion and from the excretion of (47)Ca and (44)Ca in a 24-h urine sample collected on day 2. (44)Ca in urine was determined by inductively coupled plasma mass spectrometry.
  
  
  RESULTS
  Mean (+/- SD) calcium absorption was 75 +/- 9% with the dual-isotope method and was 74 +/- 8% with the whole-body radioisotope retention method. There was a high degree of agreement between the methods.
  
  
  CONCLUSIONS
  The dual-isotope method is a valid approach for measuring calcium absorption from a single meal.
authors.affiliation: Research Department of Human Nutrition, The Royal Veterinary and Agricultural University, Frederiksberg, Denmark.
authors.forename: Anne B
authors.initials: AB
authors.lastname: Beck
authors.forename: Susanne
authors.initials: S
authors.lastname: Bügel
authors.forename: Stefan
authors.initials: S
authors.lastname: Stürup
authors.forename: Mikael
authors.initials: M
authors.lastname: Jensen
authors.forename: Christian
authors.initials: C
authors.lastname: Mølgaard
authors.forename: Marianne
authors.initials: M
authors.lastname: Hansen
authors.forename: Ole Worm
authors.initials: OW
authors.lastname: Krogsgaard
authors.forename: Brittmarie
authors.initials: B
authors.lastname: Sandström
mesh_terms: D000284:Administration, Oral; D000328:Adult; D002118:Calcium / Q000032:analysis* / Q000652:urine; D002127:Calcium Isotopes / Q000032:analysis; D002132:Calcium Radioisotopes / Q000032:analysis; D002136:Calcium, Dietary / Q000032:analysis / Q000493:pharmacokinetics*; D005243:Feces / Q000737:chemistry*; D005260:Female; D006801:Humans; D007201:Indicator Dilution Techniques / Q000592:standards; D007275:Injections, Intravenous; D007408:Intestinal Absorption; D008297:Male; D013058:Mass Spectrometry; D011865:Radioisotope Dilution Technique / Q000592:standards
chemical_list: D002127:Calcium Isotopes; D002132:Calcium Radioisotopes; D002136:Calcium, Dietary; D002118:Calcium