Astronauts struggle to sleep in space, potentially putting their lives at risk, a new study has found.
The research, published in The Lancet Neurology journal, reveals that many astronauts suffer serious levels of sleep deprivation, with three-quarters resorting to taking sleeping pills during spaceflight.
Dr Laura Barger, from Harvard Medical School in Boston US, who led the research said: "The ability for a crew member to optimally perform if awakened from sleep by an emergency alarm may be jeopardised by the use of sleep-promoting pharmaceuticals."
"This consideration is especially important because all crew members on a given mission may be under the influence of a sleep-promoting medication at the same time," Dr Barger added, noting that government health guidance warns patients taking sleeping pills not to engage in activities that require a high degree of mental alertness and co-ordination.
Earth orbit is known to disrupt sleep, as the sun rises and sets every 90 minutes.
However, the study showed sleep deprivation builds up in astronauts long before mission launch.
During training three months before take off and once in space, astronauts manage only around six hours of sleep; Nasa, the American space agency, schedules 8.5 hours sleep per night for astronauts.
Around half of astronauts saw their shut eye lengthen once they returned to earth.