Impact of hydration habits before bedtime on sleep quality

Evening hydration habits may influence sleep quality through nocturnal awakenings and nocturia, yet real-world evidence in young adults is limited. To quantify the association between fluid intake within 2 h of bedtime and objective (actigraphy-based) and subjective (self-reported) sleep quality indicators in young adults. A cross-sectional, mixed-method study involved 35 healthy young adults (18 males, 17 females; aged 18–40 years). Participants recorded fluid intake using provided 500 ml measuring bottles, sleep diaries, and wore actigraphy devices for 7 nights. Structured interviews assessed perceptions of hydration’s impact on sleep. Participants were classified into high (> 500 ml), moderate (250–500 ml), and low (< 250 ml) hydration groups based on evening fluid intake. Outcomes included actigraphy-derived sleep efficiency and nocturnal awakenings, self-reported nocturia frequency, perceived restfulness, and morning alertness (1–5 scale). One-way ANOVA with post-hoc Tukey’s HSD and multivariate regression adjusted for confounders (caffeine intake, BMI, stress, exercise timing). High hydration participants (n = 12) had lower actigraphy-derived sleep efficiency (82.1% ± 3.8, p = 0.003, Cohen’s d = 0.92) and more nocturnal awakenings (2.3 ± 0.8/night, p = 0.002, Cohen’s d = 1.12) compared to moderate (n = 14; 87.4% ± 4.1, 1.6 ± 0.6) and low hydration groups (n = 9; 89.2% ± 3.5, 1.3 ± 0.5). Nocturia occurred in 100% of high hydration participants vs. 57.1% (moderate) and 44.4% (low). Perceived restfulness (2.9 ± 0.6 vs. 3.6 ± 0.5 and 3.7 ± 0.4, p = 0.012) and morning alertness were lowest in the high hydration group. Multivariate analysis confirmed associations after adjusting for confounders. Excessive evening fluid intake (> 500 ml) is associated with reduced sleep efficiency, increased nocturnal awakenings, and lower next-day alertness in young adults. Moderating evening hydration may improve sleep continuity.