Night time fluid increase is not sufficient to affect sleep or induce nocturia in healthy women

Objectives: Nocturia, a need to urinate that wakes one from sleep, is the most common lower urinary tract symptom, thought to result from a complex interplay of multiple etiologies. Regardless of pathogenesis, the primary treatment recommendation is fluid restriction 2-4 hours before bedtime. Current evidence for this is poor, with little data directly evaluating the impact of nighttime fluid increase on nocturia. We aim to determine if nocturia can be induced by a novel fluid increase protocol in healthy participants.

Methods: This pilot study is part of an IRB-approved study investigating sleep patterns and nocturia. From February to March 2023, five patients without underlying bladder or sleep pathology participated in a fluid increase protocol. For the first 3 days, participants performed a standard three-day bladder diary and the total fluid consumption was averaged. For the last 5 days, participants increased fluid intake by 30% of their averaged total fluid within 2 hours of bedtime. Time of fluid increase, nighttime voids, and voided volume were recorded. Safety and adverse events were reported at the conclusion of the protocol.

Results: In healthy women < 65 years old, increasing fluids by 30% within 2 hours before bedtime was not sufficient to consistently induce nocturia. Nocturia occurred every night in 40% of participants. 40% of participants had nocturia or an additional evening void in only 1 of 5 protocol nights. Those with nightly nocturia had an average 49-minute decrease in total sleep time, but there was no clinically significant difference in time spent in slow wave/deep sleep cycles (88.8 minutes baseline vs 95.5 minutes post-protocol, p = 0.81) or REM sleep (128.35 minutes vs 113.4 minutes, p = 0.79). Additionally, nightly nocturia caused no clinically significant difference in sleep latency (3.0 minutes vs 4.1 minutes, p = 0.35). Nocturia caused an average first uninterrupted sleep period of 3.8 hours, but no difference in Epworth Sleepiness Scale. Participants were asked to limit total fluid intake to less than 3L; 60% performed evening fluid increases of 700-1000 mL without adverse events or changes in sleepiness.

Conclusions: Increasing evening fluid consumption by 30% of the daily fluid intake within 2 hours of bed was well tolerated but not sufficient to induce nocturia or change patterns in sleep phases in women without underlying sleep and bladder pathology. Further investigation is warranted to evaluate current fluid restriction recommendations.