title: Human hydration indices: acute and longitudinal reference values.
abstract: It is difficult to describe hydration status and hydration extremes because fluid intakes and excretion patterns of free-living individuals are poorly documented and regulation of human water balance is complex and dynamic. This investigation provided reference values for euhydration (i.e., body mass, daily fluid intake, serum osmolality; M +/- SD); it also compared urinary indices in initial morning samples and 24-hr collections. Five observations of 59 healthy, active men (age 22 +/- 3 yr, body mass 75.1 +/- 7.9 kg) occurred during a 12-d period. Participants maintained detailed records of daily food and fluid intake and exercise. Results indicated that the mean total fluid intake in beverages, pure water, and solid foods was >2.1 L/24 hr (range 1.382-3.261, 95% confidence interval 0.970-3.778 L/24 hr); mean urine volume was >1.3 L/24 hr (0.875-2.250 and 0.675-3.000 L/24 hr); mean urine specific gravity was >1.018 (1.011-1.027 and 1.009-1.030); and mean urine color was > or = 4 (4-6 and 2-7). However, these men rarely (0-2% of measurements) achieved a urine specific gravity below 1.010 or color of 1. The first morning urine sample was more concentrated than the 24-h urine collection, likely because fluids were not consumed overnight. Furthermore, urine specific gravity and osmolality were strongly correlated (r2 = .81-.91, p < .001) in both morning and 24-hr collections. These findings provide euhydration reference values and hydration extremes for 7 commonly used indices in free-living, healthy, active men who were not exercising in a hot environment or training strenuously.
authors.affiliation: Human Performance Laboratory, University of Connecticut, Storrs, CT, USA.
authors.forename: Lawrence E
authors.initials: LE
authors.lastname: Armstrong
authors.forename: Amy C
authors.initials: AC
authors.lastname: Pumerantz
authors.forename: Kelly A
authors.initials: KA
authors.lastname: Fiala
authors.forename: Melissa W
authors.initials: MW
authors.lastname: Roti
authors.forename: Stavros A
authors.initials: SA
authors.lastname: Kavouras
authors.forename: Douglas J
authors.initials: DJ
authors.lastname: Casa
authors.forename: Carl M
authors.initials: CM
authors.lastname: Maresh
mesh_terms: D001834:Body Water / Q000737:chemistry / Q000378:metabolism*; D002940:Circadian Rhythm / Q000502:physiology*; D003116:Color; D003681:Dehydration / Q000175:diagnosis / Q000652:urine; D004326:Drinking; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008297:Male; D009994:Osmolar Concentration; D012016:Reference Values; D013046:Specific Gravity; D016482:Urinalysis; D014556:Urine / Q000737:chemistry*; D014563:Urodynamics / Q000502:physiology; D014882:Water-Electrolyte Balance / Q000502:physiology*; D055815:Young Adult