A novel dual radio- and stable-isotope method for measuring calcium absorption in humans: comparison with the whole-body radioisotope retention method

Am J Clin Nutr. 2003 Feb;77(2):399-405. doi: 10.1093/ajcn/77.2.399.


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.

Design: 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.

Conclusion: The dual-isotope method is a valid approach for measuring calcium absorption from a single meal.

Publication types

  • Comparative Study

MeSH terms

  • Administration, Oral
  • Adult
  • Calcium / analysis*
  • Calcium / urine
  • Calcium Isotopes / analysis
  • Calcium Radioisotopes / analysis
  • Calcium, Dietary / analysis
  • Calcium, Dietary / pharmacokinetics*
  • Feces / chemistry*
  • Female
  • Humans
  • Indicator Dilution Techniques / standards
  • Injections, Intravenous
  • Intestinal Absorption
  • Male
  • Mass Spectrometry
  • Radioisotope Dilution Technique / standards


  • Calcium Isotopes
  • Calcium Radioisotopes
  • Calcium, Dietary
  • Calcium