title: Inter- and intraindividual correlations of background abundances of (2)H, (18)O and (17)O in human urine and implications for DLW measurements.
abstract: OBJECTIVE
  The method of choice for measuring total energy expenditure in free-living individuals is the doubly labeled water (DLW) method. This experiment examined the behavior of natural background isotope abundance fluctuations within and between individuals over time to assess possible methods of accounting for variations in the background isotope abundances to potentially improve the precision of the DLW measurement.
  
  
  METHODS
  In this work, we measured natural background variations in (2)H, (18)O and (17)O in water from urine samples collected from 40 human subjects who resided in the same geographical area. Each subject provided a urine sample for 30 consecutive days. Isotopic abundances in the samples were measured using Off-Axis Integrated Cavity Output Spectroscopy.
  
  
  RESULTS
  Autocorrelation analyses demonstrated that the background isotopes in a given individual were not temporally correlated over the time scales of typical DLW studies. Using samples obtained from different individuals on the same calendar day, cross-correlation analyses demonstrated that the background variations of different individuals were not correlated in time. However, the measured ratios of the three isotopes (2)H, (18)O and (17)O were highly correlated (R(2)=0.89-0.96).
  
  
  CONCLUSIONS
  Although neither specific timing of DLW water studies nor intraindividual comparisons were found to be avenues for reducing the impact of background isotope abundance fluctuations on DLW studies, strong inter-isotope correlations within an individual confirm that use of a dosing ratio of 8‰:1‰ (0.6 p.p.m.: p.p.m.) optimizes DLW precision. Theoretical implications for the possible use of (17)O measurements within a DLW study require further study.
authors: Los Gatos Research, Mountain View, CA, USA.
authors: E S F
authors: ES
authors: Berman
authors: Division of Endocrinology, Metabolism and Diabetes, University of Colorado Anschutz Medical Campus, Aurora, CO, USA.|Division of Geriatric Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, USA.
authors: E L
authors: EL
authors: Melanson
authors: Division of Geriatric Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, USA.
authors: T
authors: T
authors: Swibas
authors: Los Gatos Research, Mountain View, CA, USA.
authors: S P
authors: SP
authors: Snaith
authors: Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen, Scotland, UK.|State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China.
authors: J R
authors: JR
authors: Speakman
mesh_terms: D000328:Adult; D001834:Body Water / Q000378:metabolism*; D003903:Deuterium / Q000652:urine*; D004734:Energy Metabolism; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010103:Oxygen Isotopes / Q000652:urine*; D014867:Water / Q000378:metabolism*; D055815:Young Adult
chemical_list: D010103:Oxygen Isotopes; D014867:Water; D003903:Deuterium