A team of US and Netherlands-based scientists has published a review paper highlighting ways to protect astronauts from the negative cardiovascular health impacts associated with exposure to space radiation during long-distance space travel.

Cardiovascular impacts

Space radiation is currently regarded as the most limiting factor for long-distance space travel because exposure to it is associated with significant negative effects on the human body. However, data on these effects are currently only available for those members of the Apollo programme that travelled as far as the Moon – too small a number from which to draw any significant conclusions about the effects of the space environment on the human body. In addition, although exposure to space radiation, including galactic cosmic rays and solar “proton storms”, has previously been linked to the development of cancer and neurological problems, data on the consequences of space radiation exposure for the cardiovascular system are lacking.

In an effort to address these limitations, researchers based at the University Medical Center (UMC) Utrecht, Leiden University Medical Center, Radboud University and the Technical University Eindhoven in the Netherlands, as well as Stanford University School of Medicine and Rice University in the US, have carried out an exhaustive review of existing evidence to establish what we know about the cardiovascular risks of space radiation. They present their findings in the journal Frontiers in Cardiovascular Medicine.

As first author Manon Meerman, a graduate student at UMC Utrecht, explains, the majority of current knowledge comes from studies of people who have received radiotherapy for cancer, where cardiovascular disease is a common side-effect, or from animal and cell culture studies that demonstrate the major negative effects of exposure to space radiation on the cardiovascular system. Such effects include fibrosis, or stiffening, of the myocardium and accelerated development of atherosclerosis, the main cause of myocardial and cerebral infarction.

“You can argue that if NASA, ESA and other space agencies want to expand space travel, both in terms of location – for example, to Mars – and time, astronauts will be exposed to the specific space environment for longer periods of time. However, we currently do not know what the effects of exposure to these space-specific factors are,” says Meerman.

“NASA currently sees space radiation as the most limiting factor for long-distance space travel, but the exact short- and long-term effects are not fully understood yet. We are therefore exposing astronauts to extremely uncertain risks. However, research into the effects of space radiation has increased over the past few years and we’re constantly gaining more knowledge on this topic,” she adds.

Advanced models

According to Meerman, another important factor in this discussion is the fact that we currently cannot adequately protect astronauts from space radiation. Shielding with radiation-resistant materials is very difficult since exposure levels are far higher than on Earth and the type of radiation is much more penetrating. Pharmacological methods of protecting the cardiovascular system are hampered by the fact that no effective radioprotective compounds have yet been approved.

“The most important conclusion is that we actually do not know enough about the exact risks that long-distance space travel pose for the human body. Therefore, in our opinion, we should keep looking for new ways to protect astronauts from the harmful space environment before we expand human space travel,” says Meerman.

Moving forward, Meerman stresses that research on the effects of space radiation should incorporate advanced models that provide a more accurate representation of the cardiovascular impacts of space radiation – such as those based on lab-created human cardiac tissue and organ-on-a-chip testing technologies. Studies should also examine the effects of combinatorial exposure to different space radiation particles, as well as combined exposure to space radiation components and other space-specific factors, like microgravity, weightlessness and prolonged hypoxia.

“These are all crucial studies to be conducted in order to really understand the risks we’re exposing astronauts to,” says Meerman. “Therefore, we believe we are not there yet and we should debate whether it is safe to expand human space travel significantly.”