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. 2013 Aug;113(8):2143-51.
doi: 10.1007/s00421-013-2649-0. Epub 2013 Apr 23.

Circadian variation and responsiveness of hydration biomarkers to changes in daily water intake

Erica Perrier  1 , Agnès Demazières, Nicolas Girard, Nathalie Pross, Dominique Osbild, Deborah Metzger, Isabelle Guelinckx, Alexis Klein
Affiliations

Circadian variation and responsiveness of hydration biomarkers to changes in daily water intake

Erica Perrier et al. Eur J Appl Physiol. 2013 Aug.

Abstract

Biomarkers of hydration change in response to acute dehydration; however, their responsiveness to changes in fluid intake volume, without exercise or heat exposure, has not been adequately described. Moreover, patterns of circadian variation in hydration biomarkers have not been established. The study aims were to (1) assess the response of hydration biomarkers to changes in daily water intake; and (2) evaluate circadian variation in urinary and salivary biomarkers. Fifty-two adults (24.8 ± 3.1 years; 22.3 ± 1.6 kg/m(2); 79 % female), grouped based on habitual fluid intake (low drinkers, n = 30, <1.2 L/day; high drinkers, n = 22, >2.0 L/day), completed a 5-day inpatient crossover trial. On days 1 and 2, low drinkers received 1.0 L/day of water while high drinkers received 2.5 L/day. On days 3 through 5, intake was reversed between groups. Plasma and saliva osmolality were assessed daily at predetermined times, and all urine produced over 24 h was collected in timed intervals. ANOVA with intake (1.0 vs. 2.5 L/day), day, and time revealed that (1) urine concentration (osmolality, specific gravity, color) and volume, but not plasma nor saliva osmolality, responded to changes in water intake; (2) urinary hydration biomarkers and saliva osmolality vary as a function of the time of day; and (3) urine osmolality measured in samples collected during the afternoon most closely reflects the corresponding 24 h value. Overall, urinary hydration biomarkers are responsive to changes in water intake, and stabilize within 24 h of modifying intake volume. Moreover, short afternoon urine collections may be able to replace 24 h collections for more convenience in hydration assessment.

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Figures

Fig. 1
Fig. 1
Daily schedule of water intake and hydration biomarker collections. Standardized meals were provided at 0800, 1200, and 2000 hours, with a snack at 1600 hours. Spot collections for blood (2 samples) and saliva (13 samples) were performed at predetermined times. All urine produced during the 24 h period was collected in five ‘short collection’ intervals, corresponding to morning (AM), early afternoon (PM-1); late afternoon (PM-2); evening (EVE); and overnight (ON)
Fig. 2
Fig. 2
Urine osmolality (a), specific gravity (b), and color (c) measured from short urine collections during baseline (D1–D2) and intervention (D3–D5). Significant main effects of time were present for all three measures (p < 0.001 in both groups). Urinary hydration biomarkers were significantly higher during the overnight and morning collection intervals, compared with early and late afternoon. LOW low drinkers, HIGH high drinkers, AM morning, PM-1 early afternoon, PM-2 late afternoon, EVE evening, ON overnight
Fig. 3
Fig. 3
Urine production (mL/h) and volume of water (mL) ingested during the five daily urine collection intervals. LOW low drinkers, HIGH high drinkers, AM morning, PM-1 early afternoon, PM-2 late afternoon, EVE evening, ON overnight. *Significantly different from AM (p < 0.05), #significantly different from EVE (p < 0.05)
Fig. 4
Fig. 4
Daily fluctuations in SOsm. In both groups and under both intake conditions, SOsm was highest at 0700 hours, with significant drops in SOsm in both groups after breakfast and lunch. LOW low drinkers, HIGH high drinkers. *Higher (p < 0.05) compared to all other measured timepoints, with the exception of 1200 hours (low drinkers). #Lower (p < 0.05) than 0800 hours (both groups) and 1000 hours (low drinkers). **Lower (p < 0.05) than 1200 and 1400 hours
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