Criterion values for urine-specific gravity and urine color representing adequate water intake in healthy adults.

Growing evidence suggests a distinction between water intake necessary for maintaining a euhydrated state, and water intake considered to be adequate from a perspective of long-term health. Previously, we have proposed that maintaining a 24-h urine osmolality (UOsm) of ⩽500 mOsm/kg is a desirable target for urine concentration to ensure sufficient urinary output to reduce renal health risk and circulating vasopressin. In clinical practice and field monitoring, the measurement of UOsm is not practical. In this analysis, we calculate criterion values for urine-specific gravity (USG) and urine color (UCol), two measures which have broad applicability in clinical and field settings. A receiver operating characteristic curve analysis performed on 817 urine samples demonstrates that a USG ⩾1.013 detects UOsm>500 mOsm/kg with very high accuracy (AUC 0.984), whereas a subject-assessed UCol⩾4 offers high sensitivity and moderate specificity (AUC 0.831) for detecting UOsm >500 m Osm/kg.

Equivalence of afternoon spot and 24-h urinary hydration biomarkers in free-living healthy adults.

BACKGROUND/OBJECTIVES: Urinary biomarkers of hydration (urine osmolality, UOsm; urine specific gravity, USG) follow circadian variations. For individuals, researchers and health-care professionals, there is value in identifying time frames during which spot values of UOsm and USG are representative of 24-h values in healthy young adults. SUBJECTS/METHODS: Eighty-two free-living adults (22.3±2.9 years, 22.2±1.5 kg/m(2)) collected individual urine voids over a 24-h period. UOsm and USG were measured on each void and on the pooled 24-h sample. To determine the time of day when a spot sample was likely to be equivalent to the 24-h value, daytime voids were binned by time and equivalence was tested for each 2-h window. Equivalence was a priori defined as being within 100 mOsm/kg (UOsm) and within 0.003 units (USG) of 24-h values. RESULTS: For both UOsm and USG, voids between 1400 and 2000 hours produced values that were equivalent to the 24-h sample, whereas earlier voids tended to overestimate 24-h UOsm and USG. For windows 1401-1600 hours, 1601-1800 hours and 1801-2000 hours, the mean difference (95% confidence interval) between spot and 24-h UOsm (mOsm/kg) was -25 (-72; 22), 28 (-35; 92) and 12 (-41; 66), respectively, whereas for USG the difference was 0.0014 (-0.0028; -0.0001), 0.0001 (-0.0017; 0.0019) and 0.0005 (-0.0018; 0.0009), respectively. CONCLUSIONS: In free-living healthy French adults, 24-h urine concentration can be approximated from a mid- to late-afternoon spot urine sample. This finding suggests that an afternoon sample may be an accurate and practical tool for hydration monitoring, useful to individuals and health-care practitioners.

Intake of water and beverages of children and adolescents in 13 countries.

PURPOSE: To describe the intake of water and all other beverages in children and adolescents in 13 countries of three continents. METHODS: Data of 3611 children (4-9 years) and 8109 adolescents (10-17 years) were retrieved from 13 cross-sectional surveys (47 % males). In three countries, stratified cluster sampling design was applied to randomly recruit schools classes. A quota method was applied in the other countries to randomly recruit participants. Details on the intake of all fluid types were obtained with a fluid-specific record over 7 consecutive days. RESULTS: In the total sample, the highest mean intakes were observed for water (738 ± 567 mL/day), followed by milk (212 ± 209 mL/day), regular soft beverages (RSB) (168 ± 290 mL/day) and juices (128 ± 228 mL/day). Patterns characterized by a high contribution of water, RSB or hot beverages to total fluid intake were identified among the countries with close geographical location. Adolescents had a significantly lower milk intake and higher intake of RSB and hot beverages than children in most countries. The most consistent gender difference observed was that in both age groups males reported a significantly higher RSB consumption than females. CONCLUSION: On average, water was the fluid consumed in the largest volume by children and adolescents, but the intake of the different fluid types varied substantially between countries. Since the RSB intake was as large, or even larger, than water intake in some countries, undertaking actions to improve fluid intake habits of children and adolescents are warranted.