Thirst perception tracks well with acute dehydration even after a cold shower

Abstract

Purpose: to determine if Engell’s 9-point subjective scale of thirst perception (TP) is able to detect varying levels of hypohydration after exercise in the heat. In addition, we wished to evaluate the susceptibility of TP measures to changing due to time or a cold shower. Methods: in a repeated-measures design, eight physically active college students (24.5±3.6 years, mean±standard deviation), reported to the laboratory after an overnight fast (10 hours or longer), on four non-consecutive days. They exercised intermittently in a controlled climate chamber (mean temperature and relative humidity: 32±3 °C and 65±6%) to a randomly assigned dehydration equivalent to 0, 1, 2 and 3% of body mass (BM). Following exercise, subjects ingested a fixed volume of water equivalent to 1.20% BM in 30 minutes and TP was evaluated every 30 minutes over 3 hours. Results: Baseline characteristics were not different among conditions (p>0.05). Differences were found for TP (in arbitrary units) among conditions (p=0.012): TP at 0% BM (2.6±1.4) was lower than TP at 2 (6.3±2.3) and 3% BM (8.6±0.5) after exercise (p=0.018 and p<0.0005, respectively). TP at 0 (1.0±0.0) and 1% BM (1.4±0.5) was different from TP at 3% BM (5.1±2.8) after water intake (p=0.025 and p=0.032, respectively). TP was already the same for all conditions 30 min after drinking, (1.1±0.3, 1.1±0.3, 2.6±1.4, and 3.3±2.3 for 0, 1, 2 and 3% BM, respectively, p>0.05); it remained so for 3h. There was no significant difference in TP between two consecutive measures separated by a 30-minute period with a cold shower, but without drinking (t=0.89, 0.00, 1.87, and 1.00 for 0, 1, 2, and 3% BM, respectively, p>0.05). Conclusion: This subjective scale of thirst perception is able to detect levels of hypohydration equivalent to 2% BM or greater. TP is robust but it decreases quickly after drinking (and remains low for 3h) even in the absence of euhydration.