Inter- and intraindividual correlations of background abundances of?²H,?¹⁸O and?¹⁷O in human urine and implications for DLW measurements

科學家應用LGR同位素分析儀測定人體尿液中的²H,¹⁸O和¹⁷O豐度間的相互作用對DLW測量方法的影響

E S F Berman, E L Melanson, T Swibas, S P Snaith and J R Speakman

Background/Objectives:

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.

Subjects/Methods:

In this work, we measured natural background variations in 2H, 18O and 17O 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 2H, 18O and 17O were highly correlated (R2=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.:1?p.p.m.) optimizes DLW precision. Theoretical implications for the possible use of 17O measurements within a DLW study require further study.?

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