Habitual Fluid Intake Does Not Affect Sleep Parameters In Young Women

Sleep is essential for optimal physical performance, cognitive function, recovery, and overall health. Similarly, hydration status has been shown to influence physical and cognitive functions. Dehydration can lead to impaired cognition and possibly impaired sleep. However, the effect of habitual total fluid intake (TFI) on sleep and recovery measures have not been examined. PURPOSE: To examine the effect of TFI on sleep and recovery measures in young women. METHODS: Twenty-two young women (22.8 ± 4.6 yrs; 60.0 ± 9.5 kg; 164.6 ± 6.1 cm) collected habitual dietary data across a 1-wk period. Based on the hydration habits, TFI was calculated, and participants were categorized in either High Drinker (HD; ≥2.5 L/day; n = 13; age: 23.0 ± 3.6 yrs) or Low Drinker (LD; ≤ 1.6 L/day; n = 9; age: 23 ± 3 yrs). Sleep and recovery measures were collected using a wearable sleep-tracking device that participants wore for 5 consecutive days. Sleep and recovery measures were compared between HD and LD, using a two-tailed independent t-test and effect sizes (ES). ES were identified as either small (0.2-0.49), medium (0.5-0.79), and large (>0.8). RESULTS: No significant differences were found in resting heart rate (HD: 63.7 ± 4.6 bpm; LD: 61.9 ± 5.2 bpm, p = 0.40), heart rate variability (HD: 58.2 ± 14.1 ms; 69.6 ± 40.9 ms, p = 0.44), slow wave sleep (HD: 1.5 ± 0.4 hrs, LD: 1.4 ± 0.3 hrs; p = 0.55), sleep consistency (HD: 65.2 ± 15.6%, LD: 63.3 ± 7.3%; p = 0.71), and sleep efficiency (HD: 90.5 ± 3.1%, LD: 90.4 ± 2.0%; p = 0.91). Rapid eye movement (REM) sleep (HD: 2.0 ± 0.4 hrs, LD: 1.6 ± 0.7 hrs; p = 0.17) and REM percentage (HD: 26.1 ± 3.8%, LD: 21.5 ± 7.8%; p = 0.13) displayed the largest differences, with REM percentage having a large effect size (d = 0.80). CONCLUSION: Habitual fluid intake might not have any role in sleep measurement in this study. However, based on ES, REM sleep and REM percentage potentially display a trend. Still, more research is necessary to further determine any correlations.