Astronaut sleep study reveals how spaceflight alters rest patterns

Astronauts face unique challenges during space missions, and their sleep patterns are no exception. A recent study conducted by researchers at Harvard College, Harvard Medical School, and NASA Ames Research Center sheds new light on how spaceflight reshapes astronauts’ sleep patterns. Published in the Journal of Sleep Research, the findings reveal the dynamic and adaptive changes in sleep architecture that occur during extended missions in space.

Sleep is critical for physical health, emotional regulation, and cognitive performance, especially in high-stakes environments like space missions. However, astronauts frequently report disrupted sleep patterns during spaceflight. Factors such as stress, microgravity, circadian misalignment, and environmental conditions aboard spacecraft are thought to contribute to reduced sleep quality and duration.

“Prior studies have shown that astronauts average about six hours of sleep while in space, but there haven’t been many studies examining how the brain may change during sleep in space. It is difficult to evaluate these types of changes because it usually requires using electrodes on a person’s scalp to measure brain activity,” said study author Erin Flynn-Evans, the director of the Fatigue Countermeasures Laboratory at NASA’s Ames Research Center.

Instead, five male participants, averaging 43.5 years old, who were selected for missions aboard the Mir space station between 1996 and 1998, were trained to use a device called the Nightcap, which is designed to measure sleep stages based on eye and body movements. Data collection occurred during three 12-night blocks before their flights, two 12-night blocks after returning to Earth, and multiple nights during their space missions.

“These data were collected using a system that measured changes in eye movements to help us determine when astronauts were in REM or non-REM sleep,” Flynn-Evans explained. “These sleep stages represent different processes in the brain. For example, deep sleep is associated with waste clearance in the brain, while REM and Stage 2 sleep are associated with learning and memory consolidation, among other functions.”

“Understanding how spaceflight affects the brain during sleep allows us to anticipate any problems that may arise as a result of not getting enough of a particular type of sleep. It also helps us identify targets to inform countermeasure development to improve sleep quality and quantity during spaceflight.”

The researchers analyzed a total of 256 nights of sleep recordings. Participants followed a consistent 24-hour schedule aligned with Moscow time during spaceflight, with no major changes to their daily routines.

The study confirmed that astronauts experienced significant changes in sleep architecture during spaceflight. On average, participants slept about one hour less in space than on Earth, with total sleep time decreasing from 6.7 hours preflight to 5.7 hours inflight. Sleep efficiency—a measure of the proportion of time spent asleep while in bed—dropped from 89% preflight to 73% during spaceflight. Sleep onset latency, or the time it took to fall asleep, nearly doubled in space, and wakefulness after sleep onset tripled.

“There were marked shifts in sleep architecture compared to baseline, and some of these evolved over the course of the mission,” said lead author Oliver Piltch, an undergraduate researcher at Harvard College. “Our findings were consistent with previous studies that focus on the issue of sleep continuity. We found significant decreases in sleep efficiency during spaceflight despite similar times in bed.”

Both REM and NREM sleep were reduced during spaceflight, with REM sleep comprising 19.6% of total sleep time in space compared to 26.4% preflight. Over the course of the missions, however, REM sleep gradually recovered to preflight levels, though this recovery came at the expense of NREM sleep.

“Sleep is important for optimal cognitive function, both on Earth and in space,” Flynn-Evans told PsyPost. “Spaceflight may influence how we sleep in space.”

Interestingly, the study found no lasting effects on sleep architecture after participants returned to Earth. Sleep patterns returned to preflight levels, suggesting that the observed changes were specific to the spaceflight environment and did not result in permanent alterations to the participants’ sleep systems.

However, the researchers emphasized the need for further investigation to validate these findings. “We had a small sample size because only a few astronauts are in space at a time,” Flynn-Evans noted. “We will need additional research to confirm our findings before we act on them. We would like to do additional studies using electroencephalogram (EEG) to confirm our findings in a larger sample.”

The study, “Changes to human sleep architecture during long-duration spaceflight,” was authored by Oliver Piltch, Erin E. Flynn-Evans, Millennia Young, and Robert Stickgold.