It started out mainly as a curiosity after an observation in the laboratory. Mice bombarded with a dose of radiation comparable to what they’d get on a mission to Mars had signs of endothelial dysfunction in their blood vessels predisposing them to atherosclerosis. Michael D. Delp, PhD, who has studied the effects of spaceflight on the cardiovascular system in animal models for more than 2 decades, wondered if the type of damage he was seeing in mice might have also occurred in astronauts who had flown into deep space.
Abbasi J. Do Apollo Astronaut Deaths Shine a Light on Deep Space Radiation and Cardiovascular Disease?. JAMA. 2016;316(23):2469-2470. doi:10.1001/jama.2016.12601