Cosmic radiation could harm the heart on trips to Mars, rat study suggests
Wisconsin researchers simulated cosmic rays and weightlessness. Heart scarring appeared months after exposure.
Symbolic image · Photo: NASA/JPL/Texas A&M/Cornell / Wikimedia Commons, Public domain (cropped and resized)
Cosmic radiation could damage astronauts' hearts and immune systems on a long trip to Mars, according to a study by the Medical College of Wisconsin published in the journal PLoS One. Researchers irradiated middle-aged rats at Brookhaven National Laboratory with protons and heavy ions such as silicon and iron to simulate cosmic rays. They mimicked weightlessness by unloading the animals' hind limbs for 30 days, then monitored the rats for about a year, roughly equivalent to 25 human years.
At a high dose of 1.5 gray, scar tissue formed around the heart's blood vessels; by 270 days the scarring had doubled and was squeezing the coronary vessels. According to the report, the effect was caused entirely by radiation, not weightlessness. At a lower dose comparable to a three-year Mars mission, scarring was not visible at first, but after a year it had developed in 83% of the animals.
Months after exposure, the animals' spleens had lost about two-thirds of their natural killer cells, a key part of immune defense. White blood cells also showed permanent mutations in genes linked to clonal hematopoiesis, which can raise the risk of heart attack and stroke. The study has limits: the radiation was delivered in a single dose rather than continuously, and only male animals were studied.