Premium
Do we excrete what we eat? Analysis of stable nitrogen isotope ratios of human urinary urea
Author(s) -
Hülsemann Frank,
Koehler Karsten,
Flenker Ulrich,
Schänzer Wilhelm
Publication year - 2017
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.7891
Subject(s) - urea , chemistry , urine , urinary system , isotopes of nitrogen , nitrogen , zoology , stable isotope ratio , composition (language) , human blood , endocrinology , biochemistry , physiology , biology , organic chemistry , physics , linguistics , philosophy , quantum mechanics
Rationale Natural stable nitrogen isotope ratios ( δ 15 N) are frequently used for the determination of provenance and dietary assessment of recent and ancient humans. Although individual δ 15 N values typically correspond to the dietary δ 15 N composition, they are also affected by metabolic conditions. Preferred matrices for the measurement of human δ 15 N values have been hair, nail or blood. The goal of this study was to validate a novel approach for the assessment of the δ 15 N values from urinary urea, the principal end‐product of human N metabolism. Methods The method, which involves the precipitation of urea from urine using xanthydrol, was validated using fortified urea solutions. Intra‐ and inter‐individual variance of the δ 15 N values of urinary urea was determined from samples obtained from multiple human subjects. Results Precipitation with xanthydrol did not alter the δ 15 N values of urea. The mean δ 15 N value in urinary urea from human subjects from Germany was +4.4 ± 0.6 ‰, which corresponds to the estimated dietary composition. It falls below previously reported δ 15 N values for human tissue and blood samples. Longitudinal analyses over 7 days illustrate short‐time changes linked to varying protein intake. Conclusions Our results indicate that δ 15 N values can be measured reliably from human urine and that the method is suitable to monitor rapid dietary and metabolic changes of an individual. Our findings further confirm that urinary urea is depleted in 15 N compared with human tissue but within the range of the δ 15 N composition of the diet. Copyright © 2017 John Wiley & Sons, Ltd.