The immune system is particularly vulnerable, since it relies on cell-to-cell interactions for ridding the body of harmful pathogens.
One study, for instance, found that astronauts who had recently returned from space had white blood cells that were less effective at seeking out and destroying E. coli bacteria.
Left untreated, E. coli can cause severe cramps, vomiting, and diarrhea as well as kidney and blood-cell damage that can lead to fatal complications.
Vitamin Boosts, Faster Rides
Keeping astronauts healthy on long-duration missions will be a major challenge for NASA and other space agencies, agreed Gerald Sonnenfeld, an immunologist and vice president of research at Binghamton University.
"There is a potential for a problem in the immune system to create an issue in a long-term spaceflight, and this must be seriously investigated," said Sonnenfeld, who was not involved in the new report.
But the problems are not insurmountable, Sonnenfeld said. For instance, the report authors note that using vitamins and compounds to help boost the immune system is one promising avenue for future research.
Alternatively, the risks to astronauts could be reduced by shortening the time they have to spend in space, said Millie Hughes-Fulford, an immunologist at the University of California, San Francisco, and a former NASA astronaut.
NASA is currently experimenting with a so-called plasma drive that could potentially cut the transit time to Mars, for example, down from about nine months to three, Hughes-Fulford said.
Research into astronaut health was once much more active, Binghamton University's Sonnenfeld added. (Find out why one astronaut recently spent months in space wired with electrodes and recording the smells of his underwear.)
But "as [space agencies] saw that there were really no serious issues on shorter term flights and even longer space station missions, they cut back on the interest and funding," he said.
"I think [astronaut health is] back on the radar screen now that [NASA] is considering longer-term missions."
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