This condition, known as orthostatic hypotension, occurs in up to half of those astronauts on short-term missions (two weeks or less) and in nearly all astronauts after long-term missions (four to six months).
The study solves the biological mystery of how this happens by showing that low gravity compromises the ability of arteries and veins to constrict normally, inhibiting the proper flow of blood.
Prevention and treatment strategies developed for astronauts may also hold promise for elderly populations on Earth who experience orthostatic hypotension more than any other age group.
"The idea of space exploration has been tantalising the imagination of humans since our early existence," said researcher Michael D Delp from the University of Florida.
"As a scientist, I have had the opportunity to learn that there are many medical challenges associated with travel in a weightless environment, such as orthostatic hypotension, bone loss and the recently recognized visual impairment that occurs in astronauts," Delp said in a statement.
Delp and colleagues examined arteries and veins from mice housed at Kennedy Space Center in Florida with blood vessels from groups of mice flown on three of the last five space shuttle missions - STS-131, STS-133 and STS-135.
Mice flown on the STS-131 and STS-135 missions were tested immediately after returning to Earth, whereas mice from STS-133 were tested one, five and seven days after landing.
Not only did they find that these mice experienced the equivalent of orthostatic hypotension in humans, they also discovered that it takes as many as four days in normal gravity before the condition is reversed.
"There has been considerable interest in sending humans to the moon, asteroids, and Mars," said Gerald Weissmann, Editor-in-Chief of The FASEB Journal, "but what we're finding is that extended space missions have their own inherent risks above and beyond the obvious.
The research was published in The FASEB Journal.
