The rarified group of men who blasted off from Earth on the Apollo missions in the 1960s and 70s have suffered from much higher rates of death by cardiovascular disease than not only other astronauts, but a slice of the U.S. population as a whole, a new study finds.

Researchers looked at the rate of death from cardiovascular disease among astronauts who never flew in space, went to space but stayed in low-Earth orbit, and the Apollo astronauts, who went further away from Earth than anyone else. Of the 24 Apollo astronauts who flew into deep space, eight have died and seven were included in the study. The eighth astronaut - Edgar Mitchell - died after the data analysis had been completed. 

That’s much higher than the other groups the researchers considered. Astronauts who never flew, or who flew in low-Earth orbit, had much lower rates of death from heart disease than the Apollo astronauts. And, for those non-Apollo astronauts, the rates of death from cardiovascular disease were much lower than death from Americans in general between the ages of 55 and 64.

The Earth’s magnetosphere helps to protect people on the ground and in orbit from cosmic radiation. "We know very little about the effects of deep space radiation on human health, particularly on the cardiovascular system," Michael Delp, the first author on the new study and a professor at Florida State University, said in a statement. "This gives us the first glimpse into its adverse effects on humans."

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But the Apollo numbers are small. The study took into account just seven astronauts from the Apollo mission who have died, and says that 43 percent of them succumbed to cardiovascular disease— which is three people.

This new study comes at a time when NASA is eyeing a manned trip to Mars or an asteroid at some point in the future— and SpaceX turns its gaze to Mars too— and suggests that exposure to space radiation is an important factor to consider. As the study, which was published in the journal Scientific Reports, says, “These data suggest that human travel into deep space may be more hazardous to cardiovascular health than previously estimated.”

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