Changes to human sleep architecture during long-duration spaceflight.

Both rapid eye movement and non-rapid eye movement sleep are important for cognitive function and well-being, yet few studies have examined whether human sleep architecture is affected by long-duration spaceflight. We recorded 256 nights of sleep from five crew members before (n = 112 nights), during (n = 83 nights) and after (n = 61 nights) ~6-month missions aboard the Mir space station, using the Nightcap sleep monitor. We compared sleep outcomes (including total sleep time, efficiency, latency, rapid eye movement and non-rapid eye movement) during spaceflight with those on Earth. We also evaluated longitudinal changes over time in space. We found that wakefulness increased by 1 hr in space compared with on Earth. Over time in space, rapid eye movement was initially reduced and then recovered to near preflight levels at the expense of non-rapid eye movement sleep. Upon return to Earth, sleep architecture returned to preflight distribution. Our findings suggest that spaceflight may alter sleep architecture and should be explored further.