Influence of progressive fluid restriction on mood and physiological markers of dehydration in women

Abstract

The present study evaluated, using a well-controlled dehydration protocol, the effects of 24 h fluid deprivation (FD) on selected mood and physiological parameters. In the present cross-over study, twenty healthy women (age 25 (SE 0.78) years) participated in two randomised sessions: FD-induced dehydration v. a fully hydrated control condition. In the FD period, the last water intake was between 18.00 and 19.00 hours and no beverages were allowed until 18.00 hours on the next day (23-24 h). Water intake was only permitted at fixed periods during the control condition. Physiological parameters in the urine, blood and saliva (osmolality) as well as mood and sensations (headache and thirst) were compared across the experimental conditions. Safety was monitored throughout the study. The FD protocol was effective as indicated by a significant reduction in urine output. No clinical abnormalities of biological parameters or vital signs were observed, although heart rate was increased by FD. Increased urine specific gravity, darker urine colour and increased thirst were early markers of dehydration. Interestingly, dehydration also induced a significant increase in saliva osmolality at the end of the 24 h FD period but plasma osmolality remained unchanged. The significant effects of FD on mood included decreased alertness and increased sleepiness, fatigue and confusion. The most consistent effects of mild dehydration on mood are on sleep/wake parameters. Urine specific gravity appears to be the best physiological measure of hydration status in subjects with a normal level of activity; saliva osmolality is another reliable and non-invasive method for assessing hydration status.

Fig. 1

Study design. Note: water intake was only allowed during the control period. Mealtimes were as follows: 07·00 hours for breakfast, 09·45 hours and 15·45 hours for snacks and 12·00–13·30 hours for lunch. RAVLT, Rey Auditory Verbal Learning Test; PVT, Psychomotor Vigilance Test; VAS, visual analogue scales; B&L VAS, Bond and Lader VAS; sVAS: sensation VAS; eVAS: emotional VAS; POMS: Profile of Mood States; KSS, Karolinska sleepiness scale; VS, vital signs.

Fig. 2

Effects of the progressive acute water restriction on urinary parameters: (a) urine specific gravity (USG) and (b) urine colour (U_col). Values are means for each experimental condition and for differences between the two conditions, with standard errors represented by vertical bars. *** Mean values were significantly different between the two experimental conditions at the corresponding time point (P< 0·001; ANCOVA). □, Control; , fluid deprivation; ▲, fluid deprivation minus control.

Fig. 3

Effects of the progressive acute water restriction on subjective thirst sensation (visual analogue scale). Values are means for each experimental condition and for differences between the two conditions, with standard errors represented by vertical bars. The time point 18.00 hours corresponds to ad libitum water intake in both conditions. *** Mean values were significantly different between the two experimental conditions at the corresponding time point (P< 0·001; ANCOVA). , Control condition; , fluid deprivation; , fluid deprivation minus control.