title: Interpreting common hydration biomarkers on the basis of solute and water excretion.
abstract: OBJECTIVE
  This investigation evaluated 12 hydration biomarkers, to determine which represent 24-h whole-body water balance (that is, measured as water retention or clearance (WR-C) by the kidneys).
  
  
  METHODS
  Healthy males (n=59; body mass, 75.1±7.9 kg; height, 178±6 cm; age, 22±3 years; body mass index, 23.9±2.4 kg/m(2)) met with a registered dietitian each morning (days 1-11) to optimize completeness and accuracy of food and fluid records, then went about ordinary daily activities. These men visited the laboratory for blood samples and collected all urine produced on days 1, 3, 6, 9 and 12. The reference standard (WR-C) was calculated using 24-h urine volume, 24-h urine osmolality, and serum osmolality (single morning venous sample).
  
  
  RESULTS
  Statistical regression analyses indicated that, among the 12 hydration biomarkers, only 24-h urine osmolality (r(2)=0.60, P<0.0001) and 24-h urine specific gravity (r(2)=0.52, P<0.0001) strongly predicted WR-C. The 24-h fluid intake, 24-h body mass change, 24-h urine color and 24-h urine volume were weak (P>0.05) predictors of WR-C, similar to serum osmolality and other single measurements (range of r(2) values, 0.19-0.0001).
  
  
  CONCLUSIONS
  These observations of healthy, active young men demonstrate that WR-C is strongly related to the 24-h concentration of urine, which in turn reflects the excretion of total solids in the diet. Although morning urine assessments provided information about a single time point, 24-h urine osmolality and 24-h urine specific gravity were the best predictors of 24-h body water balance.
authors: Department of Kinesiology, Human Performance Laboratory, University of Connecticut, Storrs, CT 06269-1110, USA. lawrence.armstrong@uconn.edu
authors: L E
authors: LE
authors: Armstrong
authors: E C
authors: EC
authors: Johnson
authors: A L
authors: AL
authors: McKenzie
authors: C X
authors: CX
authors: Muñoz
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000652:urine*; D001823:Body Composition; D015992:Body Mass Index; D001834:Body Water; D003681:Dehydration / Q000652:urine*; D006801:Humans; D008297:Male; D009994:Osmolar Concentration; D013046:Specific Gravity; D011795:Surveys and Questionnaires; D016482:Urinalysis; D014556:Urine / Q000737:chemistry; D014867:Water / Q000378:metabolism; D055815:Young Adult
chemical_list: D015415:Biomarkers; D014867:Water