Urinary markers of hydration during 3-day water restriction and graded rehydration.
Level 2 - randomized trial
Randomized controlled trial
PubMed 31428854 · doi:10.1007/s00394-019-02065-7
What was done
115 adult males and females were observed during 1 week of habitual fluid intake, 3 days of fluid restriction (1000 mL/day), and a fourth day randomized into five graded rehydration groups: no additional water (CON), +500 mL (G+0.50), +1000 mL (G+1.00), +1500 mL (G+1.50), or +2250 mL (G+2.25). Urine was collected across 1 baseline day, the final 2 days of fluid restriction, and the rehydration day, and measured for urine osmolality, urine color (Ucol), and urine specific gravity.
What was found
Only the G+1.50 and G+2.25 groups achieved significant differences from CON across all urinary markers. Participants whose Ucol shifted from > 4 to < 4 had a significantly greater mean fluid increase (+1435 ± 812 mL) compared to those who remained at Ucol ≥ 4 (+667 ± 722 mL, p < 0.001). An additional 500 mL was insufficient, whereas approximately 1500 mL of additional fluid (total intake 2990 to 3515 mL/day) was required to restore urine color indicative of euhydration.
Why it matters
This study provides experimental dose-response data on the fluid volume necessary to reverse multi-day mild dehydration, demonstrating that modest increases like 500 mL/day do not reliably restore hydration biomarkers.
Limits
The abstract does not provide exact baseline participant characteristics, sex-specific responses, or numerical values for urine osmolality and specific gravity across groups. Dietary solute intake and environmental factors were not detailed in the abstract.
Cited by
- supports Urine does not need to be completely clear to indicate adequate hydration.