Spacey Sneezes: Why Do Astronauts Get Sick in Space?
By Harpreet Singh
Cosmofluencer (Season 03)
The secrets of space beckon us with various challenges and fascination as humanity travels farther into the cosmos. As we keep on diving deep into the wonders of exploration, numerous new challenges are coming up, upon which the health of our astronauts greatly depends. Among these, is the complex relationship between space flight and the human immune system.
Astronauts are made to thrive in an environment that is very different from Earth, beyond our atmosphere, one in which there is intense radiation, and microgravity present.
This blog explores the scientific findings and their implications for the future of space exploration and human health as we set out to understand the profound impacts of space flight on the human immune system.
Why does this matter at all?
Picture this, you’re hurtling through space, living your dream of cosmic exploration. But instead of battling aliens, you find yourself battling a runny nose!
Turns out, space weakens our immune system, making astronauts more susceptible to everyday ailments. Don’t worry, these space explorers are tough, but research is underway to understand how space travel disrupts immunity.
By cracking this code, we can ensure these brave adventurers stay healthy and focused on the real mission i.e., pushing the boundaries of human knowledge!
The Culprits: Unveiling the Threats
Numerous studies have shown that the underlying immunological dysregulation may result from physiological stressors common to space travel, such as radiation, modified diet, microgravity, disturbed circadian rhythms, and isolation.
This is in turn evident in some on ground-based simulations that mimic the spaceflight parameters and conditions. These include ground analog human data analysis, consisting of:
- Haughton‐Mars Project Analog (Canadian Arctic): Located in Haughton meteorite impact structure, having a spaceflight analog of isolation, extreme environment, and altered circadian rhythms. Moreover, this is an excellent analog for planetary exploration, especially for Mars and Moon.
- Antarctic Winter‐over Analog: AWO is said to be the closest analog to spaceflight conditions available on Earth due to its extremely harsh environment, that mimics the space environment.
- NEEMO (Undersea Station): By utilizing Aquarius, the world’s only permanent undersea station, this analog is not less than a mission in itself for the ‘aquanauts’ because this dive protocol typically lasts 7-14 days. Easy return to the surface is not possible, requiring the nominal resurfacing of approximately 18 hours of decompression.
All of the aforementioned spaceflight conditions can be replicated by these analog stations, with the obvious exception of microgravity. In order to mitigate this anomaly, our astute investigators synthesized data from ground-based cell culture experiments and analyzed its influence on the behavior of the cells under microgravity!
What is the evidence?
So far we have seen the different methodologies and ideologies for mimicking the conditions that are suspected to be the reason for the core of this problem.
From the given data, dealt with below, the fact that human immune mechanisms behave strangely in apparently abnormal environments can be very well appreciated.
Reduced CMI Response
Our bodies naturally defend against invaders (antigens) like microbes. Cell-mediated immunity (CMI), a key defense system, fights these antigens by mechanisms such as phagocytosis.
But during long‐duration flight, cell‐mediated immunity has been demonstrated to be reduced in some subjects, owing to increased stress hormone levels, most probably. Stress hormones (catecholamines) increase blood glucose levels, which results in a markedly suppressed neutrophil phagocytic activity.
This is supported by tests showing a reduced response to injected antigens (tetanus, tuberculin, Candida), indicating a weaker immune response.
Th1 vs Th2 imbalance
The human immune system orchestrates its defense through specialized T cells. These T cells fall into two categories: Th1 cells, which activate cell-mediated immunity (CMI), and Th2 cells, which stimulate antibody production. Ideally, these Th1 and Th2 responses exist in a balanced state.
However, research suggests that spaceflight disrupts this equilibrium, leading to a dominance of the Th2 pathway. This results in an increase in circulating antibodies, which unfortunately offer limited protection against viral infections, potentially compromising astronaut health.
Altered Cytokine Levels
Spaceflight throws tiny immune messengers (cytokines) out of whack, promoting Th2 responses in astronauts.
So, What is the problem?
With a firm grasp of the scientific mechanisms, let’s now turn our attention to the practical implications for astronaut health.
Viral Reactivation – A serious threat
Our bodies harbor hidden viruses, kept in check by a healthy immune system. However, the weakened immune response during spaceflight (reduced CMI) can lead to the reactivation of these dormant viruses, such as Epstein-Barr Virus (EBV), Varicella-Zoster Virus (VZV), and Cytomegalovirus (CMV).
Risk of Hyperimmune Disorders
Dysregulated Th1/Th2 response balance may be associated with many conditions, including rheumatoid arthritis, multiple sclerosis, asthma, lupus, and allergies.
Risk of Malignancies
Mice flown to space showed changes in genes linked to cancer. This raises concerns about a potential increased risk of cancer development in astronauts.
What can be done?
Space travel throws a curveball at our immune system. But fear not, innovative solutions are taking flight! Astronauts can benefit from a toolbox of strategies:
Exercise Training
Regular exercise is crucial for maintaining CardioRespiratory Fitness (CRF) and upper body musculature. Regular exercise prevents latent viral inactivation by mobilizing the cells responsible for immunosurveillance and correcting the altered stress response.
Probiotic Approach
Probiotic therapy is being dragged into the limelight to fight gut ‘Dysbiosis’, being another contributing factor in the immunosuppression of astronauts.
Use of Beta-Blockers
Beta-blockers can be used to block the activity of catecholamines, providing antagonizing action against stress-induced deranged immunity.
Preventive Measures
Vaccination, such as Zostavax against VZV, is administered to all crewmembers before space flight. Preventing the exposure to radiation in space is a must.
Nutritive Approach
Hypocaloric nutrition can promote oxidative stress on cells and immunosuppression. Cysteine and glycine-rich diet are essential for the synthesis of Glutathione, which is helpful in sequestering the oxidative species.
A diet rich in carotenoids, vitamin C, flavonoids, and folate markedly improves the immune response.
References
- NASA Human Research Roadmap | Risk of Adverse Health Event Due to Altered Immune Response
- PubMed | Latent virus reactivation in astronauts on the International Space Station; Mehta, Laudenslager, Stowe, Crucian, Feiveson, Sams, Pierson
- PubMed | Exercise as a countermeasure for latent viral reactivation during long duration space flight; Agha, Mehta, Rooney, Laughlin, Markofski, Pierson, Katsanis, Crucian, Simpson
- YouTube – ScienceCasts at NASA | Your Immune System… In Space