Erectile dysfunction risk may rise on lengthy space missions, rat study reveals

Deep space exploration may increase the risk of astronauts developing erectile dysfunction, new research on rats suggests. 

In experiments in the lab, male rats' exposure to simulated galactic cosmic radiation (GCR) and weightlessness impaired the function of the erectile tissue in the penis, according to a new study published Wednesday (Nov. 22) in The FASEB Journal.  

These effects were observed even after a year-long recovery period, suggesting that deep space exploration could have long-lasting health impacts for astronauts. 

With crewed missions to outer space planned for the coming years, "this work indicates that sexual health should be closely monitored in astronauts upon their return to Earth," co-senior study author Justin La Favor, an assistant professor who studies neurovascular dysfunction at Florida State University, told Live Science in an email. 

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As the space industry prepares to send astronauts around the moon as early as 2024 and to Mars by 2040, more attention is being paid to the potential long-term impacts of deep space exploration on the human body. During such missions, astronauts would be exposed to weightlessness due to the low levels of gravity in space, as well as high levels of GCR. 

On Earth, the planet's thick atmosphere helps to deflect GCR — energetic subatomic particles — back into space, protecting life below. But in space, there is less protection, so astronauts are more exposed to its effects. For example, a six-month stay on the International Space Station will give astronauts a dose of radiation from cosmic rays equivalent to about 25 lifetimes on Earth's surface, Live Science previously reported. High exposure to GCR could lead to certain cancers, neurological damage and cardiovascular disease.

Both GCR and weightlessness "are associated with adverse health outcomes, although the effects on erectile function had not previously been investigated," La Favor said. 

On Earth, erectile dysfunction — the inability to establish and maintain an erection — affects more than half of men between 40 and 70 years old. The effects of space exploration could therefore be an important consideration for male astronauts, especially if the condition persists in the long term. 

Over four weeks, the authors of the new study exposed 86 adult male rats to either hindlimb unloading, an experimental way of simulating weightlessness by lifting them up by their tails so that they are suspended with their head down at a 30 degree angle, or a control where they were able to touch the floor. Hindlimb unloading mimics two of the major physiological effects of low gravity, namely that the animals don't bear weight so there is no resistance on their muscles and bones, and it mimics shifts in body fluid and pressure that happen in an absence of gravity, La Favor said. 

At the same time, using the ground-based GCR simulator at the NASA Space Radiation Laboratory in New York, the rats were exposed to one dose of either low or high amounts of cosmic radiation. 

Around 12 to 13 months later, the authors euthanized the mice and extracted samples from the corpus cavernosum, the erectile tissue of the penis and the internal pudendal artery, the major artery that regulates the flow of blood into the penis during an erection. They discovered that GCR, and to a lesser extent weightlessness, impaired the function of both types of tissue mainly by increasing oxidative stress — when there is a build up of free radicals in the body which can damage cells. 

Follow-up experiments, however, showed that it was possible to counteract some of the effects caused by GCR using certain types of antioxidants. 

The study only considered the health effects of GCR and weightlessness following a long recovery period, so it is possible that the short-term effects could be more severe, the authors wrote in the paper. 

Going forward, the authors would like to look further into the exact causes of the observed effects and investigate ways to prevent them. Female astronauts will also be on board upcoming missions, so it will also be important to investigate the potential impacts of deep space exploration on their sexual function too, they wrote. 

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