The majority of astronauts in space are sleep deprived and rely on sleeping pills for a good night's rest.

The study, conducted in 2010 when the last U.S. Space Shuttle made it into orbit, looked into the sleep cycles of astronauts.

It found that astronauts in the shuttle had less than six hours sleep on the usual night while astronauts in the International Space Station slept a few minutes more. Some 75 percent of all the crews took sleeping pills to let them sleep, usually zolpidem.

Like Us on Facebook

The study, financed but not carried out by NASA, raises some safety issues for missions in the future, said researchers.

"In ground-based studies, we know that sleeping less than six hours is associated with performance detriments," said lead author Laura Barger, a research fellow at Brigham and Women's Hospital and instructor at Harvard Medical School in Boston.

The chronic use of sleeping pills is an issue on its own, she added.

"If an astronaut had to be awakened in the middle of the night for some emergency situation, his performance could be impaired."

Barger and her colleagues noted that next-day drowsiness is a concern. They had quoted a warning on zolpiderm from the Food and Drug Administration that said its users should be warned against doing dangerous jobs that need complete mental alertness or motor skills such as driving cars and operating heavy machinery.

The drug has also been linked to "sleep-driving," according to the FDA. Sleep driving is a phenomenon similar to sleepwalking but it's more complicated because the sleeping individual gets behind the wheel and goes for a drive. When the person wakes up, he has no recollection of his actions.

The study included 64 astronauts inside a shuttle and 21 astronauts inside the ISS. The astronauts from different countries kept medication and sleep logs and wore movement monitors to confirm sleep times.

Although scientists were unable to collect information about the astronauts' performance, they had proof that the astronauts in the study were sleep deprived.

Once the astronauts returned to Earth, they slept more like numerous other sleep-deprived workers on their days off, Barger said.

In NASA's rules, astronauts are required to have 8.5 hours of sleep per night. Work demands and conditions in space such as heat, cold, noise and weightlessness might get in the way, however.

NASA said it is "committed to fully understanding the impacts of long-duration spaceflight on our astronauts."

"The agency works hard to identify and implement countermeasures that can ensure astronauts are able to get the same quality and quantity of sleep in space as they do on Earth." 

TagsSpace, International Space Station, astronaut, Drugs, Sleeping, Sleeping pills, Science