Plain water intake immediately before bedtime decreased depressive mood in the morning, prolonged REM sleep latency, and reduced the duration of REM sleep, though it also increased the likelihood of nocturia.
Pre-bedtime plain water intake was associated with lower depressive mood scores in a large-scale survey of Japanese adults.
Consuming 280 mL of plain water immediately before bedtime decreased depressive mood in the morning compared to no beverage intake for at least 2 hours before bedtime.
Plain water intake immediately before bedtime prolonged REM sleep latency.
Plain water intake immediately before bedtime reduced the duration of REM sleep.
Plain water intake immediately before bedtime increased the likelihood of nocturia.
This research suggests that drinking a glass of plain water (280 mL, roughly 9–10 oz) right before going to bed may help reduce feelings of depression or low mood in the morning. The study, conducted with middle-aged Japanese men, first surveyed 2,000 people to see whether pre-bedtime water drinking habits were linked to depressive mood, and then ran a controlled experiment comparing drinking water immediately before bed versus avoiding all beverages for at least two hours before bed. The water-drinking group reported better mood upon waking and also showed measurable changes in their sleep architecture, specifically taking longer to enter REM sleep and spending less time in REM sleep overall. However, the research also found a notable downside: people who drank water before bed were more likely to wake up during the night to use the bathroom (nocturia). This means the practice comes with a trade-off — potential mood benefits in the morning weighed against possible sleep disruptions from nighttime bathroom trips. The authors emphasize that individuals should weigh these advantages and disadvantages for themselves. This research suggests that a simple, low-cost habit like drinking water before sleep could be a practical tool for supporting mental wellbeing, but the finding that it alters REM sleep patterns raises questions about the underlying mechanism connecting hydration, sleep structure, and mood. Further research would be needed to understand how broadly these findings apply beyond middle-aged Japanese men and whether the REM sleep changes are directly responsible for the mood improvements.
Kaida K, Itoi K, Soeta Y, Ooie T, Oishi K. (2026). Effects of plain water intake before bedtime on sleep and depressive mood among middle-aged Japanese men.. PloS one. https://doi.org/10.1371/journal.pone.0340490