Studies on rats show potentially crippling damage to testes and ovaries from weightlessness and radiation.
Researchers have some advice for astronauts planning families after they return from long stays in space -- freeze your eggs or sperm before you go.
Studies on rats haven't sorted out whether it's the radiation, the impacts of microgravity on the hormonal system, or a combination of both that is responsible for damage to testes and ovaries during spaceflight and in ground-based experiments that simulate weightlessness.
"Along with the lens of the eye, these are the most sensitive of all the organs to radiation," said space researcher Joseph Tash, director of the Interdisciplinary Center for Male Contraceptive Research and Drug Development at the University of Kansas Medical Center in Kansas City.
"If you have an astronaut that is showing cataracts, that means that that individual's ovaries or testes already have surpassed the known exposures that would have an impact on their gonadal function," Tash told Discovery News.
Whatever the trigger, preserving healthy eggs and sperm before a long-duration flight is among the top recommendations researchers have for astronauts contemplating long-duration stays aboard the International Space Station or future deep space missions.
Doctors are recommending that female astronauts who are going to be serving on the space station for a long period of time harvest and cryo-preserve ovarian biopsies or oocytes, and that males preserve semen, Tash said.
"If you preserve any of those eggs or sperm, you know that it won't have suffered any radiation damage if you collect it before a long mission," Tash said.
Until recently, most astronauts serving aboard the space station were beyond their family planning years, a natural consequence of the amount of time and seniority it took to be assigned a long-duration flight.
With the retirement of the space shuttle, however, younger astronauts who many not be finished or even started having children are being assigned station flights that last six months. NASA also plans to begin year-long increments.
"We're maybe reaching the point where reproductive health risks may be observed," Tash said.
"Spaceflight may shorten reproductive lifespan -- that's what we've seen in rodents. Whether that occurs in humans is obviously an important question that we would like to look at," he added.
Currently, the space station is not outfitted for follow-up rodent studies, but researchers will be getting a chance next year to fly mice, gerbils and other critters on a Russian 30-day satellite.
Task and other researchers plan to present their findings from rodent experiments flown during the final shuttle missions at the American Society for Gravitational and Space Research meeting in New Orleans later this month.