Use of urine markers to assess hydration status in healthy children
The primary purpose of this study was to characterize the 24-hour urinary output in healthy children and compare these findings to existing standards for hydration assessment. A secondary purpose of the study was to document one day of total water intake at the time of the urine collection. This is the first documentation of 24-hour urinary output with a focus on hydration status in healthy U.S. children.
Sixty-one healthy children ages 4.9 to 11.7 years volunteered to provide 24-hour urine specimens on two days (C1 and C2) and to record dietary intake including all water sources for one day. Urine volume (Uvol), specific gravity (Usg) and osmolality (Uosm) were compared to existing Dietary Reference Intakes (DRI) recommendations to determine hydration status. Food records were analyzed to determine total water intake compared to DRIs.
Mean ± SD 24-hr Uvol, Usg, and Uosm were 614 ± 204 mL, 1.020 ± 0.005, and 782 ± 207 mOsm/kg (C1) and 626 ± 235 mL, 1.019 ± 0.005 and 758 ± 204 mOsm/kg (C2), respectively. Based on Usg >1.030, only one child was hypohydrated during C1, and none during C2. In C1 44% of the children and in C2 42% of the children exhibited Usg >1.020 and ≤1.030. Mean total water intake was 1535 ± 406 mL with 28% from food and 72% from beverages. Eighty two percent of the children ages eight and younger, 78% of the girls ages nine to eleven, and 89% of the boys ages nine to eleven consumed less than the Adequate Intake for water.
Chronically concentrated urine may increase risk of certain conditions such as urolithiasis in predisposed children, and low water intake may pose increased risk of dehydration in physically active youth. The current study suggests that these children did not exhibit a high incidence of hypohydration, but did exhibit a relatively high prevalence of concentrated urine. It appears that a portion of children may benefit from consuming more fluid to meet the AI.