Do we excrete what we eat? Analysis of stable nitrogen isotope ratios of human urinary urea

• Published in: Rapid communications in mass spectrometry Vol. 31; no. 14; pp. 1221 - 1227
• Main Authors: Hülsemann, Frank, Koehler, Karsten, Flenker, Ulrich, Schänzer, Wilhelm
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 30.07.2017
• Subjects: Adult; Hair; Human subjects; Humans; Isotope ratios; Male; Mass Spectrometry - methods; Metabolism; Middle Aged; Nitrogen; Nitrogen Isotopes - metabolism; Nitrogen Isotopes - urine; Reproducibility of Results; Urine; Variance; Xanthenes - chemistry; Young Adult; Germany
• ISSN: 0951-4198; 1097-0231; 1097-0231
• DOI: 10.1002/rcm.7891

Rationale Natural stable nitrogen isotope ratios (δ15N) are frequently used for the determination of provenance and dietary assessment of recent and ancient humans. Although individual δ15N values typically correspond to the dietary δ15N composition, they are also affected by metabolic conditions. Preferred matrices for the measurement of human δ15N values have been hair, nail or blood. The goal of this study was to validate a novel approach for the assessment of the δ15N 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 δ15N values of urinary urea was determined from samples obtained from multiple human subjects. Results Precipitation with xanthydrol did not alter the δ15N values of urea. The mean δ15N 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 δ15N 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 δ15N 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 15N compared with human tissue but within the range of the δ15N composition of the diet. Copyright © 2017 John Wiley & Sons, Ltd.