Variability In Daily Fluid Intake And Inadequate Hydration Influence Objective Sleep

PURPOSE: Previous data suggests that shorter total sleep time is associated with greater odds of inadequate hydration, but it is unclear how variability in daily fluid intake is associated with sleep metrics. Thus, the purpose of this study was to examine the relationships between 3-day variability in individual daily fluid intake, hydration status, and objective sleep metrics. METHODS: Twenty-seven healthy males (mean ± SD; age, 23 ± 4y; height, 176 ± 6 cm; weight, 78.7 ± 12.9 kg; body fat, 16.6 ± 8.7%) collected 24 hr urine samples to assess hydration status (Urinary Osmolality [UOSMO]) and self-reported habitual fluid intake using a validated fluid intake log. Sleep was captured over the same period using a wrist-worn actigraph. Separate random-intercept linear mixed fixed-effects models assessed the impact of within-subject variability and between-subject differences in daily fluid intake (L) and UOSMO on objective sleep metrics (total sleep time, efficiency, latency, average awakening length). RESULTS: Every additional 1 L increase in daily fluid intake above grand mean (2.9 ± 1.7 L) was associated with a 3-min increase in sleep latency (β = 3.35, [95%CI; 0.7, 4.7], p = 0.009). On days when a person’s UOSMO was higher than their typical UOSMO, they experienced a longer awakening length (β = 0.005, [0.003, 0.009], p = 0.031). There were no significant associations between within-subject variability in daily fluid intake with total sleep time (β = -0.03, [-0.58, 0.04], p = 0.679), sleep efficiency (β = -0.01, [-0.05, 0.02], p = 0.454), or wake after sleep onset (β = 0.03, [-0.17, 0.25], p = 0.714). Further, there were no significant associations between hydration status and total sleep time (β = -0.23, [-0.52, 0.06], p = 0.130), sleep efficiency (β = -0.01, [-0.04, 0.01], p = 0.242), or wake after sleep onset (β = 0.05, [-0.08, 0.20], p = 0.466). CONCLUSIONS: Participants with greater than average daily fluid intake had greater sleep latency, but not total sleep time, sleep efficiency, nor wake after sleep onset. Inadequate hydration compared to one’s usual hydration status may negatively influence awakening length after sleep onset. Day-to-day variability in fluid intake should be considered in longitudinal research to help contextualize biological and behavioral modifiers of hydration status on sleep quality and quantity. This study was supported by Adams Sports Medicine Consulting LLC and Emerja Corporation, Inc.