Environmental Carbon Dioxide and Temperature Effects on Sleep Quality During Space Analogs

INTRODUCTION: Symptoms related to elevated carbon dioxide (CO2) concentrations on the International Space Station are widely stated and researched. While microgravity contributes to the observed CO2 related symptoms, an additional factor that may contribute to symptoms associated with hypercapnia is the impact of environmental CO2 on sleep. Studies evaluating how the sleep environment impacts sleep quality in terrestrial environments have shown that slightly elevated CO2 concentrations can negatively impact deep sleep quantity. METHODS: CO2 concentrations in the crewmembers' sleep quarters and crew sleep quality were recorded during two simulated space missions at the Integrated Lunar/Mars Analog Habitat. Both objective sleep stage data and perceived sleep quality were collected and correlated with environmental CO2 concentrations, temperatures, and reported health symptoms using sleep actigraphy, a perceived sleep questionnaire, and daily health surveys. RESULTS: In a space analog environment with CO2 concentrations from 450-2000 ppm, higher nightly CO2 concentrations correlated with reduced deep sleep times. However, intersubject linear regression showed varying results. Habitat temperatures had significant influence on the crew's sleep and reported health symptoms. DISCUSSION: During the 2-wk analog missions, the reductions in deep sleep when nightly CO2 concentrations increased were consistent with other terrestrial sleep studies. Due to the small sample size and variations between subjects, the evidence is not sufficient to draw definitive conclusions. This study can inform the risk analysis of environmental CO2 concentration requirements for future space habitats and provide recommendations for further research. Van Hoy SE. Environmental carbon dioxide and temperature effects on sleep quality during space analogs. Aerosp Med Hum Perform. 2026; 97(1):11-19.