However, Hjortnaes has an interest in a specific aspect of space radiation: its cardiovascular effects.

You may be surprised to learn that aside from the illnesses we typically associate with radiation, such as cancer, it can also have serious effects on the cardiovascular system. Suffering from cardiovascular illness would be catastrophic for crew members on long-haul space missions, and so it's important to identify what the risks are, and how to reduce them.

Hjortnaes and colleagues reviewed the evidence to establish what we know about the cardiovascular risks of space radiation. Much of what we know comes from studying people who have received radiation therapy for cancer, where cardiovascular disease is a common side-effect, or from mouse studies of radiation exposure.

So, what are the effects? Radiation can cause myocardial remodeling, where the structure of the heart begins to change, and tough, fibrous tissue grows to replace healthy muscle, potentially leading to heart failure. Other effects include atherosclerosis in blood vessels, which can cause stroke or heart attack. Radiation exerts its effects by causing inflammation, oxidative stress, cell death and DNA damage.

Researchers have also investigated potential ways to protect astronauts. These include drugs that an astronaut could take to protect themselves from space radiation, and antioxidants. Interestingly, an antioxidant diet, including dairy products, green vegetables such as spinach, and antioxidant supplements such as vitamin C, has potential in protecting astronauts from the damaging reactive oxygen molecules produced during radiation exposure.

Overall, the review revealed that so far, research has only scratched the surface of space radiation and the best methods to protect astronauts from it. There is little conclusive evidence of radiation-induced cardiovascular disease in astronauts themselves, as so few of them have ever gone further than low earth orbit, and mouse studies aren't an exact match for humans.

These issues prompted Hjortnaes and colleagues, who develop human cardiac tissue in the laboratory, to conclude that we need further research into these issues, and new research methods, such as organ-on-a-chip testing technologies.

"We need to develop human-based tissue platforms, such as heart-on-a-chip systems, that can simulate real human disease, outside of the human body, to unravel the mechanisms at play in spaceradiation-induced cardiovascular disease," said Hjortnaes.

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