title: Assessment of hydration biomarkers including salivary osmolality during passive and active dehydration.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, CT, USA.
authors.forename: C X
authors.initials: CX
authors.lastname: Muñoz
authors.forename: E C
authors.initials: EC
authors.lastname: Johnson
authors.forename: J K
authors.initials: JK
authors.lastname: Demartini
authors.forename: R A
authors.initials: RA
authors.lastname: Huggins
authors.forename: A L
authors.initials: AL
authors.lastname: McKenzie
authors.forename: D J
authors.initials: DJ
authors.lastname: Casa
authors.forename: C M
authors.initials: CM
authors.lastname: Maresh
authors.forename: L E
authors.initials: LE
authors.lastname: Armstrong
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000737:chemistry*; D001834:Body Water / Q000502:physiology*; D003681:Dehydration / Q000175:diagnosis* / Q000503:physiopathology; D015444:Exercise; D006339:Heart Rate; D006358:Hot Temperature; D006801:Humans; D008297:Male; D009994:Osmolar Concentration; D012463:Saliva / Q000737:chemistry*; D012680:Sensitivity and Specificity; D044967:Serum / Q000737:chemistry; D014556:Urine / Q000737:chemistry; D014882:Water-Electrolyte Balance; D055815:Young Adult
chemical_list: D015415:Biomarkers