Sauna, sweat and science II – do we sweat what we drink?

ABSTRACT

Inspired by a previous ‘Sauna, sweat and science’ study [Zech et al. Isot Environ Health Stud. 2015;51(3):439–447] and out of curiosity and enthusiasm for stable isotope and sauna research we aimed at answering the question ‘do we sweat (isotopically) what we drink’? We, therefore, pulse-labelled five test persons in a sauna experiment with beverages that were ²H-enriched at about +25,600 ‰. Sweat samples were collected during six sauna rounds and the hydrogen isotope composition δ²H_sweat was determined using an isotope ratio mass spectrometer. Before pulse labelling, δ²H_sweat – reflecting by approximation body water – ranged from –32 to –22 ‰. This is ∼35 ‰ enriched compared to usual mid-European drinking water and can be explained with hydrogen-bearing food as well as with the respiratory loss of ²H-depleted vapour. The absence of a clearly detectable ²H pulse in sweat after pulse labelling and δ²H_sweat results of ≤+250 ‰ due to a fast ²H equilibration with body water are moreover a clearly negative answer to our research question also in a short-term consideration. Given that the recovery of the tracer based on an isotope mass balance calculation is clearly below 100 %, we finally answer the question ‘where did the rest of the tracer go?’

GRAPHICAL ABSTRACT

KEYWORDS:

• Body water
• hydrogen-2
• sauna
• stabile isotope tracer technique
• sweat
• urine

Acknowledgements

First of all, we cordially thank Andre Spengler, owner of the Heide Sauna in Dölau, Halle and his colleague Dirk for kindly hosting and assisting us with our sauna experiments during the last years. We furthermore greatly acknowledge the support provided by G. Gebauer, Head of the BayCEER-Laboratory of Isotope Biogeochemistry, University of Bayreuth, and his team, namely P. Eckert, with isotope analyses. We are also very grateful to K. Auerswald for valuable discussions concerning the isotopic composition of body water, and to G. Strauch and two anonymous reviewers for the kind editorial handling and the constructive and valuable suggestions and discussions helping to improve our manuscript. Last but not least, we thank L. Wüthrich and M. Jakob for their participation as test persons in our sauna experiment and all members of the Soil Science and Soil Biogeochemistry groups of the MLU Halle–Wittenberg for participating in the BIA analyses.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. Note that the underlying mass balance calculation uses in approximation a ‘closed system’ instead of an ‘open system’. This is justified because urine and sweat are isotopically equilibrated with total body water. Respective losses do hence not lead to erroneous recoveries, because the latter are calculated with initial total body water only. By contrast, respiratory losses are isotopically depleted. Respective effects are, however, considered negligible for our experiment and the calculated recoveries.