Astronauts rely heavily on mental sharpness and emotional stability to perform their duties during space missions. And adequate sleep is critical for maintaining physical and behavioral health.

Extensive evidence indicates that regular nightly sleep of 7–8 hours is sufficient to maintain health. But despite having scheduled sleep times of 8.5 hours per night, astronauts aboard the International Space Station often sleep only about 6.5 hours, with some nights dipping below 6 hours. This sleep shortage has significant consequences for their performance and well-being.

The study
A study monitoring 24 astronauts before, during, and after their six-month missions found that reduced sleep resulted in slower reaction times, increased stress levels, and negative physical and emotional states.

Sleep under 5 hours was particularly harmful, leading to marked declines in focus and cognitive function. Just as on Earth, longer and better-quality sleep in space leads to improved mental performance and emotional health.

How Working in Space Challenges Sleep
Space travel presents unique challenges to sleep that are different from those on Earth. Operational demands, irregular schedules, and a constantly shifting environment can all disrupt sleep patterns.

Interestingly, astronauts tend to sleep longer on weekends when the workload decreases, highlighting the link between work intensity and sleep duration. But even then, they rarely reach the full 8.5 hours of sleep planned for them.

Sleep timing plays a role, too—astronauts often go to bed later than scheduled and wake up just before their next shift, leaving little room for restorative sleep.

Although astronauts report disturbed sleep about a third of the time, their overall sleep efficiency—how much of their time in bed is spent sleeping—does not appear to be severely affected in space.

Is it (less) gravity that affects sleep?
On Earth, our bodies constantly adjust to gravity, which may contribute to the need for rest. In space, the absence of gravity reduces this physical effort. It has been postulated that this explains why astronauts experience shorter REM sleep.

This theory also implies that sleep on Earth is due in part to the effort to compensate for the presence of gravity and its effects on the posture and motion of the human body.

Stress, Sleep, and Brain Health
The relationship between sleep and stress is a two-way street. As stress levels rise during a mission, sleep duration tends to decrease, which further elevates stress and affects workload.

This vicious cycle can lead to changes in brain structure and function, particularly in areas responsible for memory, decision-making, and emotional regulation. Studies have shown that long space missions can shrink certain brain regions, like the orbitofrontal cortex and medial temporal lobe, which are key to these functions.

Sleep loss can worsen these effects by reducing the brain's connectivity and increasing neural delays, the lag that occurs between a stimulus and the brain’s response to it. Ultimately, that is impairing performance.

This is why managing both sleep and stress is essential for maintaining astronauts’ brain health and cognitive abilities during space travel.


About the scientific papers:

First author: Christopher W Jones, USA
Published in: Sleep, January 2022.
Link to paper: https://academic.oup.com/sleep/article/45/3/zsac006/6505235

First author: Alessandro Arone, Italy
Published in: Clinical Neuropsychiatry. October 2021.
Link to paper: https://pubmed.ncbi.nlm.nih.gov/34984067/