Water immersion thermotherapy increases sleep duration and efficiency

However, the intervention showed no significant effect on sleep latency (time to fall asleep) or any of the subjective sleep quality measures on the Pittsburgh Sleep Quality Index (PSQI), including subjective sleep quality, sleep duration perception, daytime dysfunction, and sleep disturbances. This disconnect between objective sleep improvements and unchanged subjective ratings suggests that while WIT may extend actual sleep time, people may not feel they are sleeping better. The findings indicate that water immersion thermotherapy has measurable but limited effects on sleep, working primarily on duration and efficiency metrics rather than on how rested people feel afterward.

The effect sizes for total sleep time and sleep efficiency were small to modest (both SMD ~0.63–0.64), meaning the absolute gains—likely measured in minutes rather than hours—fall at the borderline of statistical significance. Notably, nearly all PSQI subscales showed no effect, with P-values ranging from 0.06 to 0.99, suggesting that the objective sleep gains do not translate into subjective perception of better sleep. This dissociation is important: it may indicate that water immersion delays sleep onset slightly, extends sleep duration behaviorally, yet leaves people's sense of sleep quality and morning refreshment unchanged. The heterogeneity in study populations, water temperatures, timing of immersion relative to bedtime, and duration of exposure was not fully accounted for, meaning some subgroups (e.g., people with insomnia versus those with normal sleep) might respond differently than the pooled average. The small sample size of included trials and lack of long-term follow-up data limit confidence in sustained effects.