Bad news would-be astronauts: Traveling into deep space could be bad for your heart.
In a study published Thursday in Scientific Reports , researchers found that astronauts who went to the moon were almost five times more likely to die of cardiovascular disease than astronauts who remained in low-Earth orbit on the International Space Station.
Here's a look at the highlights of the study.
What is suggested by the findings?
Earth and its magnetic field protect humans from the majority of space radiation, which damages the cardiovascular system, among other problems. The atmosphere also plays a protective role.
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Astronauts on the International Space Station live beyond the atmosphere, but still within Earth's magnetosphere. Astronauts who have flown all the way to the moon, however, are no longer protected by this magnetic shield and are subjected to more space radiation.
"Space radiation comes in really fast and it creates a lot of damage in tissues," said Michael Delp, a professor of physiology at Florida State University in Tallahassee and the first author on the paper. "It is more damaging than any radiation on Earth."
What was the comparison?
Authors looked at cause-of-death data for three groups of astronauts — those who had flown in low-Earth orbit, those who flew to the moon, and those who trained as astronauts but never flew in space.
The authors found that 43 percent of astronauts who went to the moon died of heart disease, compared with just 11 percent of those who stayed in low-Earth orbit and 9 percent of those who never flew at all.
There was no difference in cancer rates among the three groups. In all three, about 30 percent of deaths could be attributed to cancer. Scientists speculate, however, that longer exposures to radiation might result in a higher rate of cancer deaths.
What's the catch?
Relatively few people have traveled to space, and researchers considered only seven deaths of people who had been to the moon. (An eighth lunar astronaut died after the analysis was complete.)
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The low-Earth orbit group was composed of just 35 people. Another 35 were studied in non-flight astronaut group.
That small sample size casts a shadow of doubt on the conclusions of the study. "It means you have to be very cautious in your interpretations," Delp said. The group considered whether or not the findings were worth publishing, but ultimately concluded that they were.
Why does this matter?
Several countries, including the U.S., Russia, Japan and China, have said that they hope to send people into lunar orbit in the next 10 years, subjecting astronauts to longer periods of exposure to space radiation than those who flew on the Apollo missions.
But will these findings give space travelers pause? "I don't think so," Delp said. "I think astronauts are very driven, and very focused and they already take big risks."
