For more than 50 years, humans have been venturing out into space, and yet little is known about the physical toll these long flights in microgravity take on the human body.
As space agencies prepare for longer duration flights to the Moon and Mars, they need to ensure that future astronauts can survive the journey. Preliminary studies suggest time spent in space does affect our health — and perhaps even alter our brains.
A pair of recent studies identify potential solutions for a set of worrying symptoms that astronauts have shown following long duration spaceflight — namely, problems with metabolism, and bone and muscle loss.
The first study, published Tuesday in the journal Frontiers in Physiology, suggests that gut microbes could keep humans healthy during spaceflight. The second study, published Monday in the journal Proceedings of the National Academy of Sciences, suggests targeting a mechanism in human cells to help prevent the loss of bone and muscle mass.
Motion sickness — Being in a microgravity environment can often cause nausea, and reduce the appetite of astronauts, which can in turn disrupt their gut microbiome. The microbiome is the name given to community of microbes that live inside our bodies, controlling digestion and a host of other functions (and maybe even influencing our mental health).
Once in space, these changes can lead to malnourishment, making astronauts more prone to inflammation and infections, and other immune system deficits. It may also affect their mental health and cognitive abilities, according to the Frontiers study.
Previous research suggests astronauts tend to have similar gut microbiome as their peers while on space missions together. There's also some indication they experience an increase in bacteria related to intestinal inflammation, while the bacteria associated with anti-inflammatory properties tend to decrease.
"The well-being of the gut microbiome of space travelers should be among the primary goals of long-duration exploratory missions," Martina Heer, professor at the University of Bonn, and co-author of the study, said in a statement.
"To ensure the success of the mission, we must not overlook the myriad of microorganisms that reside in our gastrointestinal tract and make sure they are in balance," he said.
In order to promote astronauts' healthy guts, the study suggests a change in typical space nutrition. The diet includes more probiotics and prebiotics, which are found in foods such as yogurt, pickles, and miso, or targeted supplements.
Building up bone — The second study, which was done in mice, is focused on understanding bone and muscle health during longer duration periods of microgravity.
Being in a microgravity environment causes humans to lose some of their muscle and bone mass. This is despite attempts of enforcing regular exercise on spacecraft such as the International Space Station to help promote use of muscles.
Targeting a cellular mechanism, known as the myostatin/activin-ActRIIB pathway, may prevent the loss of muscle mass, the study suggests. Myostatin and activin are secreted proteins that limit the growth of muscles and bones. Blocking these proteins has perviously been shown to prevent the loss of muscle for people undergoing treatment for cancer.
The study tested out this method on mice who were exposed to the same microgravity environment of the ISS for a total of 33 days.
Mice treated with the injections to block the proteins showed significant recovery to their muscle and bone mass loss once they had returned to "Earth" gravity.
The authors of this study suggest that a treatment could be developed for humans during long-duration spaceflight to prevent their loss of bone and muscle mass, too, but more work is needed to understand whether this method is applicable in humans.
Abstract: The upcoming exploration missions will imply a much longer duration than any of the missions flown so far. In these missions, physiological adaptation to the new environment leads to changes in different body systems, such as the cardiovascular and musculoskeletal systems, metabolic and neurobehavioral health and immune function. To keep space travelers healthy on their trip to Moon, Mars and beyond and their return to Earth, a variety of countermeasures need to be provided to maintain body functionality. From research on ISS we know today, that for instance prescribing an adequate training regime for each individual with the devices available in the respective spacecraft is still a challenge. Nutrient supply is not yet optimal and must be optimized in exploration missions. Food intake is intrinsically linked to changes in the gut microbiome composition. Most of the microbes that inhabit our body supply ecosystem benefit to the host-microbe system, including production of important resources, bioconversion of nutrients, and protection against pathogenic microbes. The gut microbiome has also the ability to signal the host, regulating the processes of energy storage and appetite perception, and influencing immune and neurobehavioral function. The composition and functionality of the microbiome most likely changes during spaceflight. Supporting a healthy microbiome by respective measures in space travelers might maintain their health during the mission but also support rehabilitation when being back on Earth. In this review we are summarizing the changes in the gut microbiome observed in spaceflight and analog models, focusing particularly on the effects on metabolism, the musculoskeletal and immune systems and neurobehavioral disorders. Since space travelers are healthy volunteers, we focus on the potential of countermeasures based on pre- and probiotics supplements.
Abstract: Among the physiological consequences of extended spaceflight are loss of skeletal muscle and bone mass. One signaling pathway that plays an important role in maintaining muscle and bone homeostasis is that regulated by the secreted signaling proteins, myostatin (MSTN) and activin A. Here, we used both genetic and pharmacological approaches to investigate the effect of targeting MSTN/activin A signaling in mice that were sent to the International Space Station. Wild type mice lost significant muscle and bone mass during the 33 d spent in microgravity. Muscle weights of Mstn −/− mice, which are about twice those of wild type mice, were largely maintained during spaceflight. Systemic inhibition of MSTN/activin A signaling using a soluble form of the activin type IIB receptor (ACVR2B), which can bind each of these ligands, led to dramatic increases in both muscle and bone mass, with effects being comparable in ground and flight mice. Exposure to microgravity and treatment with the soluble receptor each led to alterations in numerous signaling pathways, which were reflected in changes in levels of key signaling components in the blood as well as their RNA expression levels in muscle and bone. These findings have implications for therapeutic strategies to combat the concomitant muscle and bone loss occurring in people afflicted with disuse atrophy on Earth as we