Human sperm get lost in space, pioneering study finds

Human sperm is lost in space, pioneering study finds

By Jackie Flynn Mogensen edited by Claire Cameron

On Earth, human sperm tend to know where to go when it comes to fertilizing an egg in utero. But that may not be the case in space. A new study suggests that human sperm may have difficulty navigating microgravity, a finding that raises questions about humanity’s ability to reproduce in space.

The researchers placed human sperm in a microgravity simulation chamber designed to mimic the female reproductive tract and tested the swimmers’ ability to navigate. Under microgravity conditions, sperm experienced “impaired directional navigation” – in other words, they got lost – more often than under typical gravity conditions on Earth.

And in mouse eggs, microgravity conditions had a measurable effect on insemination rates compared to Earth’s gravity: a 30 percent drop in the number of fertilized eggs over a four-hour period.

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The results, published Thursday in the journal Communication biology, could help future humans have children in space. NASA and other government space agencies maintain that no one has ever had sex in space, but future astronauts may want to start families and reproduce in a microgravity environment.

“As missions to the Moon and Mars move from aspiration to reality, understanding whether humans and the species we depend on can successfully reproduce in these environments is not a curiosity; it’s a necessity,” says Nicole McPherson, lead author of the study and a senior lecturer at the University of Adelaide in Australia, who studies reproduction.

Interestingly, adding progesterone, a hormone released by a person’s egg cells, to the uterus-like chamber helped the sperm better orient themselves in microgravity.

“Progesterone functions as a chemical signal, a sort of biological beacon that the egg releases at the time of ovulation,” McPherson explains. “Sperm have receptors on their surface that detect this signal and use it to orient themselves and swim toward the source.”

“It’s one of nature’s most elegant navigation systems,” she adds.

Progesterone only helped sperm at “considerably higher” concentrations than found in nature, McPherson says. So, although the results are interesting, “we are not at the point of suggesting progesterone as a simple solution to fertility in space.”

“However, this opens an intriguing avenue of investigation for the future,” she adds.

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