title: Comparison of stable-isotope-tracer methods for the determination of magnesium absorption in humans.
abstract: BACKGROUND
  The double-labeling (DL) method for determining magnesium absorption is less cumbersome than is the fecal monitoring method, which has been used most often, but it has not been validated.
  
  
  OBJECTIVE
  The aim of this study was to compare methods and several sampling protocols for determining magnesium absorption to establish a simple and reliable alternative to the fecal monitoring approach. Fecal monitoring was used as the standard against which the DL methods based on urine data (DLU), plasma data (DLP), and plasma kinetics with the use of a deconvolution analysis (DP) were compared.
  
  
  METHODS
  Six healthy adult men received 70 mg (26)Mg orally and 30 mg (25)Mg intravenously. Multiple blood samples and complete urine and fecal samples were collected over 12 d. Stable-isotope ratios were determined by inductively coupled plasma mass spectrometry.
  
  
  RESULTS
  Results from DLU were not significantly different from the fecal monitoring reference value (0.48 +/- 0.05; +/- SD) when based on 3-d urine pools from 72 to 144 h (0.54 +/- 0.04) and when based on the 24-h urine pools from 48 to 72 h (0.49 +/- 0.06), 72 to 96 h (0.51 +/- 0.11), and 96 to 120 h (0.50 +/- 0.06). Results with the DLP method 72 h after isotope administration also compared well with those with the fecal monitoring method (0.54 +/- 0.09). Magnesium absorption was 0.47 +/- 0.06 with the DP method, which also agreed with the fecal monitoring value.
  
  
  CONCLUSIONS
  The DL methods are an alternative to fecal monitoring when applied within the appropriate time intervals. Therefore, DLU-the simplest and least invasive approach-is recommended for determining magnesium absorption.
authors.affiliation: Nestlé Water Institute, Vittel, France.
authors.forename: Magalie
authors.initials: M
authors.lastname: Sabatier
authors.forename: William R
authors.initials: WR
authors.lastname: Keyes
authors.forename: Frédéric
authors.initials: F
authors.lastname: Pont
authors.forename: Maurice J
authors.initials: MJ
authors.lastname: Arnaud
authors.forename: Judith R
authors.initials: JR
authors.lastname: Turnlund
mesh_terms: D000284:Administration, Oral; D000328:Adult; D005243:Feces / Q000737:chemistry; D006801:Humans; D007201:Indicator Dilution Techniques / Q000592:standards*; D007262:Infusions, Intravenous; D007408:Intestinal Absorption; D007553:Isotope Labeling; D007554:Isotopes; D008274:Magnesium / Q000097:blood / Q000493:pharmacokinetics* / Q000652:urine; D008297:Male; D013058:Mass Spectrometry
chemical_list: D007554:Isotopes; D008274:Magnesium