As humanity takes its step closer toward the possibility of long-term space travel, the effects of spending a length of time in space have begun to show. For decades, astronauts with NASA and cosmonauts with other agencies have spent time in microgravity. And what occurs to the body offers crucial insights into the future of human space travel. Today, the longest single long-duration spaceflight was made by Russian Cosmonaut Valeri Polyakov, who stayed on orbit for 437 days. However, newer missions continue to offer invaluable knowledge about what changes the human body undergoes after a spaceflight in profound and unpredictable ways.
From important losses in muscle mass and bones to changes to the brain, eyes, and even the bacteria in their gut, this article uncovers how long-term exposure to space might affect astronauts’ bodies. Such research on these pioneers in space is crucial in helping humanity prepare for deep space missions, such as one mission to Mars.
Pre-Flight: Setting the Stage: The Longest Space Missions
A NASA astronaut, Frank Rubio, returned to Earth in October 2023 after spending a record 371 consecutive days aboard the International Space Station, the longest single spaceflight made by an American. He broke the previous record held by NASA’s Scott Kelly of 355 days. While two months shy of Polyakov’s record, the mission provided much-needed insights on just how human bodies are affected during long-duration spaceflight.
This year, two cosmonauts- Oleg Kononenko and Nikolai Chub-wrote their names into the history books with a record-breaking 374-day mission on the ISS. Kononenko now holds the record for total cumulative time spent in space-with more than 1,111 days. The astronauts orbited the Earth almost 6,000 times and traveled millions of miles during those missions. The real story, however, lies behind the toll that space takes on the body.
Muscles and Bones: Gravity’s Role
Among the first health effects of space travel is muscle and bone degradation. Gravity plays an imperative role on Earth in keeping our muscles and bones strong. In space, where it is essentially a weightless region, the muscles that serve as major supporters of posture-the back, neck, and legs muscles have less work to do. For instance, within just two weeks, astronauts can lose up to 20 percent of muscle mass. And during an extended six-month stay on the ISS, muscle mass can be decreased by as much as 30 percent. Rubio lost even more-much more-than that.
Another critical concern is bone health. Human beings are naturally losing bone mass on Earth with age at an approximate annual rate of about 0.5%. Loses up to 1-2% of bone mass per month in space. In space, astronauts may lose up to 10% bone mass for those who will stay on the ISS for more than six months meaning that the participants will have a higher fracture risk and decrease the rate in their recovery once they return to Earth.
To neutralize these effects, astronauts undertake an extremely demanding exercise routine – about 2.5 hours a day. These exercises include those on resistive devices for squats, deadlifts, and bench presses besides the treadmill as well as the cycling exercises. However, recent experiments suggest that exercise in space during ISS might not be strong enough to completely counteract muscle wasting. Some experts have termed high-intensity interval training and more loads to the exercising astronauts.
Related Products: Check out these NASA-inspired fitness devices that astronauts utilize on board the ISS to keep muscles and bones in space healthy.
Effects on Vision and Brain: The Invisible Threat of Microgravity
One of the lesser-known effects of space travel on vision is that fluid accumulates in the head since it is not drawn down by Earth’s gravity towards the body and consequently causes pressure on the optic nerves and change in shape of the eyes. Some astronauts have come down with the condition known as Spaceflight-Associated Neuro-ocular Syndrome wherein their visions blur and some cannot be returned to normal.
Even the brain in space changes. A 2014 Russian study that looked at cosmonauts showed different neural connectivity in areas of the brain that control movement and balance. The look is different from previous Earth-based campaigns, likely due to the strict conditions of moving around in space with no such thing as “up” or “down.” More recent studies have pointed to changes to swellings inside the brain called ventricles. These hold the cerebrospinal fluid within them. Such changes could take years to recover from.
In Scott Kelly’s one-year long mission aboard the ISS, researchers found that his cognitive performance mostly remained unchanged during the time up in space. However, his mental agility and accuracy decreased for about six months after returning to Earth. This phenomenon, sometimes referred to as “neural shuffling,” sometimes would indicate that the brain needs time to readjust to gravity.
The Gut Microbiome: Space Travel Alters Our Inner Ecosystem
Another surprising area of study is the gut microbiome-a previously under-explored player in human health. Bacteria and fungi in the intestines break down food, regulate inflammation, and have even been shown to influence the brain. Gut microbiomes change profoundly in astronauts during long-duration space missions.
In Kelly’s case, there was dramatic alteration in his gut bacteria after his year in space. This is attributed to diet factors, radiation exposure, and the practice of using recycled water onboard ISS. This is a big concern since imbalances in gut bacteria have been related to several health issues, from digestive disorders to mental health issues.
Weight, Skin, and DNA: The Final Frontier of Space Health
In space, however, weight takes on a different twist of its own: without gravity, human bodies float freely in space. It is under these conditions, though, that maintaining one’s ideal weight becomes a challenge. For instance, Scott Kelly lost 7% of his body mass during his one-year mission into space, thereby making the challenge of weight under space conditions clear.
Space also affects the skin. Kelly and other astronauts reported increased sensitivity and even rashes when returning to Earth. A loss of tactile stimulation in space is thought to be implicated.
Perhaps the most intriguing outcome of Kelly’s mission is what happens to his DNA. Telomeres, which protect the ends of chromosomes and have been demonstrated to be associated with aging, increased in length while Kelly was in space, but plummeted once he was returned. This is very important information as we send humans on longer-duration missions to places like Mars, where astronauts will be exposed to the space environment for even longer periods.
Looking Ahead: Preparing for Mars and Beyond
To prepare for more distant space travel, it is necessary to understand how the body responds to long microgravity exposure times. A trip to Mars will take at best 1,100 days round trip-hat is much longer than any ISS visit. Smaller spacecraft will be sent on such a voyage, and treadmill and stationary bicycle equipment must be not just smaller but more efficient.
The data coming from Rubio’s mission and those alike will be used by scientists to come up with better ways to combat the physical challenges of space travel. With every successive mission, we inch ourselves closer to making deep space travel a reality.
This is actually the body of growing research not only into space affecting the health of humanity but also has the potential for Earth-bound medical advantages. From bettering exercise regimens to gaining insight into the behavior of DNA in extreme environments, space research continues to unlock new knowledge that extends far beyond the stars.
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