Effect of a face mask on respiratory water loss during sleep in cold conditions.
Level 2 - randomized trial
Individual randomized crossover trial
PubMed 11995907 · doi:10.1580/1080-6032(1995)006[0189:eoafmo]2.3.co;2
What was done
Ten healthy volunteers (8 males, 2 females, aged 23–40 years, mean 30.9) completed a crossover study sleeping in individual mountaineering tents during winter nights at temperatures below 0 °C for 8 hours per night. Participants spent one night wearing a heat-and-moisture-retaining face mask designed for cold weather exercise and one night without a mask. Pre- and post-sleep body weights were measured to estimate overnight respiratory water loss.
What was found
Wearing the mask reduced overnight weight loss in 9 of the 10 subjects. The mean reduction in weight loss with the mask compared to without was 0.13 kg (SD ± 0.18 kg), which reached statistical significance using a one-tailed t-test (p < 0.05).
Why it matters
A simple moisture-retaining face mask can modestly reduce fluid loss during sleep in sub-zero wilderness environments, offering a low-cost measure to help conserve hydration in cold conditions.
Limits
The sample size was very small (n = 10), and total body weight loss was used as an indirect surrogate for respiratory water loss without controlling for cutaneous evaporation or metabolic mass loss. The statistical analysis relied on a one-tailed t-test, and real-world high-altitude conditions were not tested.
Cited by
- contradicts A person loses almost a full liter of water overnight solely through the humidity in their breath while sleeping.