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Clinical nutrition, enteral and parenteral nutrition

Assessment of hydration biomarkers including salivary osmolality during passive and active dehydration



Hydration state can be assessed via body mass change (BMΔ), serum and urine osmolality (Sosm, Uosm), urine-specific gravity (Usg) and urine volume (Uvol). As no hydration index has been shown to be valid in all circumstances, value exists in exploring novel biomarkers such as salivary osmolality (Vosm). Utilizing acute BMΔ as the reference standard, this research examined the efficacy of Sosm, Vosm, Uosm, Uvol and Usg, during passive (PAS) and active (ACT) heat exposure.


Twenty-three healthy men (age, 22±3 years; mass, 77.3±12.8 kg; height, 179.9±8.8cm; body fat, 10.6±4.5%) completed two randomized 5-h dehydration trials (36±1 °C). During PAS, subjects sat quietly, and during ACT, participants cycled at 68±6% maximal heart rate. Investigators measured all biomarkers at each 1% BMΔ.


Average mass loss during PAS was 1.4±0.3%, and 4.1±0.7% during ACT. Significant between-treatment differences at −1% BMΔ were observed for Sosm (PAS, 296±4; ACT, 301±4 mOsm/kg) and Uosm (PAS, 895±207; ACT, 661±192 mOsm/kg). During PAS, only Uosm, Uvol and Usg increased significantly (−1 and −2% BMΔ versus baseline). During ACT, Vosm most effectively diagnosed dehydration 2% (sensitivity=86%; specificity=91%), followed by Sosm (sensitivity=83%; specificity=83%). Reference change values were validated for Sosm, Usg and BMΔ.


The efficacy of indices to detect dehydration 2% differed across treatments. At rest (PAS), only urinary indices increased in concert with body water loss. During exercise (ACT), Sosm and Vosm exhibited the highest sensitivity and specificity. Sosm, Usg and BMΔ exhibited validity in serial measurements. These findings indicate hydration biomarkers should be selected by considering daily activities.

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We are grateful to the test participants for their perseverance during these difficult experiments. We acknowledge the technical assistance of Colin Shaughnessy, Corey Dwyer, Ethan Talbot, Dylan Rausch and Ted Pert during data collection. Professor Craig Denegar provided valuable statistical guidance. This research was funded by the US Government, Technical Support Working Group via a grant awarded to Cantimer, Inc., Menlo Park, CA, USA and the University of Connecticut, Office of Sponsored Programs, Storrs, CT, USA.

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Correspondence to C X Muñoz.

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Muñoz, C., Johnson, E., DeMartini, J. et al. Assessment of hydration biomarkers including salivary osmolality during passive and active dehydration. Eur J Clin Nutr 67, 1257–1263 (2013).

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  • hydration indices
  • dehydration
  • osmolality
  • saliva

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