One downside of living in space no one wants to talk about.

Living in outer space is dangerous. Space is profoundly unforgiving. Spending any kind of significant time in zero-G will ruin your body. Zero-G and microgravity negatively impacts your bone density, your cardiovascular system, muscle mass and strength decrease and possible digestive issues. 

Over the years, researchers have developed ways to circumvent these problems and keep our astronauts as healthy as possible while they are spending prolonged times in space. 

But there is one thing nobody talks about, (at least not in public.) 

If you're a guy. What happens to your “little swimmers”? What happens to them in microgravity? 

Over the decades, one of the things that science fiction writers have been obsessed about is sex in space. I'm ashamed to say that I could name at least three or four different authors that seemed very preoccupied with it. (Robert Heinlein and Piers Anthony to name two) Some even wrote about getting pregnant and giving birth in zero G or microgravity. What would the child be like? 

Well, now scientists have decided to find out what happens to human sperm when it's exposed to microgravity and the results were not too encouraging. 

According to IFLScience.com,
‘Exposure to short duration gravity load changes including microgravity, as sustained in a parabolic flight statistically significantly decreases the sperm motility and vitality of human fresh sperm samples," the team found, adding that this may have huge importance for any prolonged human settlement missions in space.’   

Rather than sending the samples into space, they used an astronaut training Technique called the “Vomit Comet”. NASA uses Parabolic flight in a passenger jet to simulate microgravity. At the top of the climb participants experience a brief period of time in microgravity. (Near zero-G.) 

The researchers discovered that subjecting the sperm to parabolic flight Including the microgravity and hypergravity. “Statistically significantly decreases the sperm motility and vitality of human fresh sperm samples," 

The preliminary conclusion is that when human beings are exposed to microgravity and hypergravity and spend months or even years in space, human reproduction would be an issue. The scientists still say they aren't sure what actually causes the little swimmers to be lazy. 

This is not a problem that anybody thinks about often when it comes to traveling in space or living on a space station. Or maybe even colonizing the moon. But it is an issue, and sooner or later will need to be solved. 

Scientists Took Semen Onto A "Vomit Comet" Flight, And The Results Were Concerning | IFLScience
How does zero gravity affect the human body? - Explaining Space