NASA astronauts return from ISS amid concerns over 9 months of physical changes

NASA astronauts Butch Wilmore and Suny Williams are finally returning to Earth after a 9-month stay at the International Space Station (ISS). They originally set off on an 8-day schedule, but their return timeline was delayed by about 9 months due to a technical defect in the Boeing 'Starliner' spacecraft they boarded. The SpaceX Dragon spacecraft, carrying the two and the astronauts who will replace them, successfully docked with the space station on the 16th. Wilmore and Williams are scheduled to embark on their return journey on the 19th.

The two appeared healthy on the surface when they met the crew members waiting to replace them. However, there is a high possibility that their bodies underwent various changes due to the long period spent in a microgravity environment. NASA and scientists have already established that long-term space stay can weaken muscles and bones, alter the nervous system, and reduce immune strength. The experiences of Wilmore and Williams are expected to provide important data for future space exploration, particularly for researching missions to distant planets like Mars.

◇The marks left by microgravity: weakening of muscles and bones

The body parts most affected in a space environment are the muscles and bones. On Earth, gravity helps support the body, but this is not the case in space, where muscles and bones weaken rapidly. Generally, muscle mass can decrease by 20% in just 2 weeks, and during stays of 3 to 6 months or more, it can decrease by up to 30%. Bones also deteriorate at a rate of 1 to 2% per month, which can reach up to 10% after 6 months. This is much faster compared to the 0.5% to 1% annual decrease in bone density due to aging on Earth.

To prevent this, astronauts staying on the ISS engage in intense exercise for 2 hours and 30 minutes each day. They use treadmills and resistance exercise devices to maintain muscle and bone mass, but recent studies suggest that current exercise methods may not completely prevent losses of muscle and bone. Research indicates that stronger resistance training and high-intensity interval training may be necessary.

In a microgravity environment, the spine can elongate, resulting in a slight increase in height. However, this can lead to back pain, and upon return to Earth, the risk of disc problems may increase. According to NASA research, most of these changes typically recover over time, but in some cases, it can take several years.

In a microgravity environment, reduced physical activity and changes in eating habits often lead to weight loss. NASA astronaut Scott Kelly spent 340 days on the ISS starting in March 2015. Scientists analyzed the effects of living in space on the human body compared to his identical twin brother, Mark Kelly, who remained on Earth during the same period.

According to a paper published in the journal Science in 2019, Scott lost 7% of his body weight while in space. This was presumed to be a result of changes in metabolism due to dietary differences in space. While NASA provides astronauts with a balanced diet to help maintain a healthy weight, they are conducting research on how gut microbiota changes over the long term.

◇Effects of the space environment on the brain and senses

The way blood circulates in space is also different from that on Earth. With the absence of gravity, blood flows evenly throughout the body. This causes more blood to accumulate in the head than when on Earth, increasing pressure in the skull and compressing the optic nerve.

According to NASA research, these changes can lead to retinal edema (swelling), decreased vision, and alterations in the structure of the eyeball, and in severe cases, may result in permanent vision damage. Relatedly, South Korea's first astronaut, Lee So-yeon, conducted an experiment to measure 'space facial edema' on the ISS in 2008. This research analyzes the phenomenon where blood and body fluids pool in the upper body, resulting in facial swelling and bulging of the eyes in a microgravity environment.

These symptoms are referred to as 'space-associated neuro-ocular syndrome (SANS),' and more than 60% of astronauts experience blurred vision. Some recover their vision within a few months of returning to Earth, but there are cases where full recovery is not achieved, and research on this issue continues.

In a microgravity environment, the human nervous system must also adapt in new ways. Research on astronauts who stayed long-term on the ISS revealed changes in the neural connections responsible for motor functions and spatial awareness in the brain.

In a study involving Russian astronauts, changes were observed in the neural connections of astronauts who stayed on the ISS for 169 days, particularly in the vestibular cortex responsible for balance. Additionally, swelling in certain areas of the brain was noted, and it has been reported that it can take up to 3 years for these changes to fully recover.

Astronauts who have spent a long time in space tend to experience slower cognitive speed or reduced reaction times for several months after returning to Earth. This is believed to occur during the process of readapting to Earth's gravitational environment.

◇Effects on skin, immune system, and genetics

Life in space also brings changes to the skin. According to NASA research, long-term astronauts often experience increased skin sensitivity, dryness, and itching. This is presumed to be due to the skin not experiencing constant friction in a microgravity environment.

The immune system is also affected. Studies indicate that the number of white blood cells tends to decrease during space stays, likely due to a combination of radiation exposure and physical stress. To compensate for this, NASA administers vaccines to astronauts and provides supplements to help maintain their immune strength. Additionally, they continue researching the long-term impact of the space environment on the immune system.

The space environment can also impact human genetic material, specifically deoxyribonucleic acid (DNA). Telomeres, located at the ends of DNA, serve to protect chromosomes, and they generally shorten with age. Interestingly, in space, telomeres have been observed to lengthen.

However, this does not mean that space stay extends lifespan. In studies on Scott Kelly, it was observed that while telomeres lengthened during his time in space, they rapidly shortened after his return to Earth. Scientists believe this is likely related to exposure to cosmic radiation or physical stress. Additional analysis is currently being conducted to study the long-term effects on aging and health.

References

Science (2019), DOI: https://doi.org/10.1126/science.aau8650