Chapter 1: The Challenges of Space Travel

Space travel poses significant challenges to human health. The absence of gravity can lead to a disorienting condition known as space adaptation syndrome, alongside muscle atrophy and bone loss over time.

NASA and its global counterparts have long been aware of these health risks and have devised effective strategies to combat them. However, as they navigate the complexities of living in zero gravity, new concerns have arisen.

A 2016 NASA study published in the International Journal of General Medicine highlighted that extended space missions disrupt the human immune system. Key indicators of immune health, including T cell signaling and cytokine levels, become unbalanced, contributing to various health issues faced by astronauts.

For instance, astronauts often experience skin rashes, allergies, and infections in the upper respiratory and urinary tracts. Additionally, dormant viral infections, such as herpes, can reactivate, leading to conditions like cold sores and shingles, which can be transmitted among crew members.

These immune complications do not necessarily resolve upon returning to Earth. Extended space missions may increase the long-term risk of various diseases, including certain cancers and gastrointestinal disorders like inflammatory bowel disease (IBD).

NASA researchers are focusing on the human microbiome—the vast array of bacteria residing in and on our bodies—believing it plays a crucial role in immune function. Their findings could have broader implications for health on Earth.

The human body hosts various microbial ecosystems, each playing distinct roles in health. Dr. Hernan Lorenzi, an assistant professor in the Department of Infectious Diseases at the J. Craig Venter Institute, has spearheaded research on the microbiome's impact during long-duration spaceflights.

In a 2019 study published in Scientific Reports, Lorenzi's team analyzed samples from nine astronauts who spent between six months and a year aboard the International Space Station (ISS). "We discovered significant changes in their microbiomes during the mission, correlating with immune response variations," he notes.

For example, the astronauts exhibited a decrease in Proteobacteria on their skin, which are essential for protecting against allergies. This shift potentially contributes to the skin issues frequently reported by astronauts.

Lorenzi's research also uncovered concerning changes in the astronauts' gut microbiomes. "We noted alterations linked to immune dysregulation that could lead to severe health issues, including cancer," he explains. A decline in beneficial bacteria associated with lower gut inflammation was observed, raising concerns about long-term gastrointestinal health.

The influence of bacteria on human health is extensive, with the gut microbiome playing a pivotal role. Imbalances in its bacterial populations have been associated with a wide array of health issues, from digestive disorders to mental health challenges.

While astronauts' microbiomes generally reverted to baseline levels within two months of returning to Earth, the underlying reasons for their initial disruptions remain unclear. "Diet may be a factor, though astronauts consume a carefully designed nutrition plan," Lorenzi suggests. Stress, the absence of gravity, and disruptions to circadian rhythms could also contribute.

One significant aspect is the sterile environment of the ISS. "People often believe that maintaining a high level of cleanliness is beneficial. However, our findings suggest that an overly sterile environment may be detrimental," Lorenzi states.

This notion isn't novel. The "hygiene hypothesis" posits that our health is influenced by interactions with bacteria, gaining traction since epidemiologist David Strachan's 1989 study linked less hygienic conditions to lower rates of immune-related diseases in children.

While some experts initially dismissed this hypothesis due to lack of understanding, recent research has illuminated the microbiome's crucial role in health. "Living in a sterile environment can diminish the richness of your microbiome due to insufficient exposure to diverse microorganisms," Lorenzi explains.

Emerging evidence suggests that early exposure to beneficial bacteria is vital for a well-functioning immune system. Conversely, the indiscriminate use of antibiotics, especially in youth, can contribute to obesity, asthma, allergies, autoimmune diseases, and neurodevelopmental disorders.

Research exploring the factors that support adult microbiome health is still in its infancy. We know that diet influences gut composition, but the impact of overly sterile environments is only recently being considered. This remains a contentious topic, yet growing evidence indicates that interactions with bacteria—through nature, pets, and social connections—are essential for microbiome health.

"If you're in an overly sterile environment, your microbiome likely becomes less diverse due to a lack of reinfection," Lorenzi asserts. "NASA is contemplating whether creating a more natural environment in spacecraft could enhance astronauts' immune health."

This presents challenges in space exploration, where minimizing contamination risks is paramount. "Reducing contamination is crucial for identifying extraterrestrial life, which necessitates maintaining sterile conditions," Lorenzi elaborates.

However, the implications of this research extend to Earth. Lorenzi's findings, combined with a multitude of studies on the human microbiome, suggest that our obsession with cleanliness could deprive us of beneficial bacterial interactions. This deprivation may contribute to the rising incidence of immune-related and chronic diseases.

Even amidst the ongoing battle against COVID-19, the CDC has indicated that the likelihood of virus transmission via contaminated surfaces is extremely low. "As a child, I was taught that all microbial contact was harmful," Lorenzi reflects. "Now we understand that only a few microorganisms cause illness, while many are vital for our survival."

Chapter 2: The Implications of Microbiome Research

NASA ScienceCasts: Station Science 101 - Monitoring Microbes for Astronaut Health

This video discusses how NASA studies the presence and behavior of microbes in space, revealing insights into astronaut health and the importance of microbiomes.

NASA Astronaut Kate Rubins Talks About Microbes

In this video, astronaut Kate Rubins shares her experiences with microbes in space, emphasizing their significance for astronaut well-being and health.