Circadian misalignment affects sleep and medication use before and during spaceflight

Area of Science:

• Space medicine
• Chronobiology
• Astronaut health

Background:

• Sleep deficiency and medication use are common in spaceflight.
• Astronaut work schedules often cause circadian misalignment, disrupting natural sleep-wake cycles.
• Understanding the impact of circadian misalignment on sleep is crucial for astronaut well-being.

Purpose of the Study:

• To investigate the association between circadian misalignment and adverse sleep outcomes in astronauts.
• To compare sleep patterns and medication use during aligned versus misaligned sleep episodes.
• To assess sleep quality and duration in relation to circadian rhythm during spaceflight.

Main Methods:

• Collected actigraphy and photometry data from 21 astronauts over 3,248 days on the International Space Station (ISS) and 11 days preflight.
• Used sleep logs for medication use and subjective sleep quality ratings.
• Calculated endogenous circadian temperature minimum using Circadian Performance Simulation Software to classify sleep episodes as aligned or misaligned.

Main Results:

• Circadian misalignment occurred during 13% of preflight sleep episodes and 19% during spaceflight.
• Sleep duration was shorter (5.4h vs. 6.4h) and sleep quality was poorer during misaligned sleep episodes.
• Sleep-promoting medication use was significantly higher during misaligned sleep episodes (24% vs. 11%).

Conclusions:

• Circadian misalignment is linked to significant sleep deficiency and increased medication use in astronauts.
• These findings highlight the need for effective countermeasures to reduce circadian misalignment.
• Mitigating circadian misalignment is essential for improving astronaut sleep and health before and during space missions.