Spaceflight is hard on the human body. The absence of gravity can induce a form of nauseating motion sickness known as space adaptation syndrome. As time passes, weightlessness can also cause muscle wasting, bone deterioration, and other health problems.
NASA and its sister space agencies around the world have long recognized these health threats, and they’ve developed effective countermeasures. But as they’ve learned to manage the challenges of zero-gravity environments, other concerns have emerged.
According to a 2016 NASA-led study in the International Journal of General Medicine, time spent in space rapidly perturbs the human immune system. Nearly every molecule and marker of healthy immune operation — from the signaling activity of T cells to the production and action of cytokines — becomes dysregulated in space, and this dysregulation seems to contribute to a number of well-documented health problems, that study found.
For example, astronauts in space often develop skin rashes, allergies, and infections of the upper-respiratory and urinary tracts. Meanwhile, long-dormant viral infections — such as those caused by the assorted herpes viruses — are prone to flare. These flares can cause cold sores, shingles, mononucleosis, and other health problems, including some that the astronauts can pass among one another.
Not all of these immune issues go away when the astronauts return to Earth. There’s concern that extended spaceflight — due in part to immune-related changes or impairments — could raise an astronaut’s long-term risks for various cancers, heart disease, or gut disorders such as inflammatory bowel disease (IBD).
There’s are many aspects of space travel that could cause an astronaut’s immune system to go haywire. But NASA researchers are increasingly focusing their attention on the human microbiome — the trillions of bacteria that live on and inside our bodies, and that play an essential part in the operation of our immune systems.
What they’ve found already may hold important lessons for all of us back here on Earth.
The human body is home to multiple distinct ecosystems of microbes, each of which is composed of many different species of bacteria. There is a skin microbiome, a gut microbiome, a nose microbiome, and several others. “In each of those ecosystems, microbes play different roles in human health,” says Hernan Lorenzi, PhD, an assistant professor in the Department of Infectious Diseases at the J. Craig Venter Institute in Maryland.
Lorenzi has led some of NASA’s research projects into the microbiome effects of long-term space travel.
For a 2019 study in Scientific Reports, he and his colleagues collected skin, nose, tongue, and gut bacteria samples from nine astronauts, each of whom spent between six months and one year aboard the International Space Station (ISS). “Basically, we found that during the mission many of these microbiomes changed, and some of these changes correlated with changes in immune responses among the astronauts,” he says. ….