Mild Dehydration by 24-h Fluid Restriction Led to Difficulty Falling Sleeping and Increased Sleep Duration

Abstract Sleep influences health and is affected by dehydration. Therefore, our aim was to assess the effects of mild dehydration and subsequent rehydration on sleep time and sleep quality using subjective measures. On 4 consecutive mornings, 18 males (mean ± SD; age, 23 ± 4 years; height, 175.8 ± 5.7 cm; weight, 80.1 ± 9.7 kg) reported to the laboratory with different hydration states (day 1 baseline; day 2 euhydrated; day 3 dehydrated; day 4 following 24-h ad libitum drinking, AD). First-morning urine specific gravity, urine color, urine osmolality, and body mass loss were used to assess hydration status. Sleep was reported using the Karolinska sleep diary, which measures sleep duration, sleep quality, perceived ease of falling asleep, sleep calmness, number of dreams, and perceived ease of falling asleep measured by a 5-point Likert scale. The visual analog scale measured fatigue before sleeping with each hydration state. Repeated measure analysis of variance with Bonferroni post hoc comparisons was used determining effects of hydration status on sleep. Sleep duration was significantly greater when dehydrated (7.5 ± 1.3 h) compared to baseline (6.4 ± 1.4 h, p = 0.001), euhydrated (6.7 ± 1.4 h, p = 0.006), and AD (6.9 ± 1.0 h, p = 0.024). More difficulty sleeping was also reported when dehydration (3 ± 1) than AD (4 ± 1, p = 0.001). Other measures were not significantly different ( p > 0.05). Fatigue was significantly greater during dehydration before sleeping (21.93 ± 13.07) compared to euhydration before sleeping (30.23 ± 14.03, p = 0.049). Our results indicate mild dehydration increased sleep duration because of increased fatigue and decreased perceived ease of falling asleep. This suggests that maintaining euhydration may assist with perceived ease of falling asleep and feelings of fatigue.