Effects of space travel on human body and rehab process: Dr Keith Siew explains

Returning to Earth after a space mission, especially an extended one, is no easy feat for astronauts.

The human body, adapted to the weightlessness of space, undergoes significant changes upon re-entry.

Dr Keith Siew, an expert in space medicine, explains the physiological and psychological challenges astronauts face and how they must readjust to life on Earth.

When astronauts splash down on Earth, their bodies struggle to reaclimatize to gravity. One of the first noticeable effects is blood pressure regulation.

“Astronauts often have lower blood pressure in space,” Dr Siew explained. Since their bodies do not need to work against gravity, their cardiovascular system becomes less efficient. Upon re-entry, they may experience dizziness or fainting spells due to sudden drops in blood pressure.

Muscle and bone loss

Another significant concern is muscle and bone loss. “You can lose up to one per cent of your bone and muscle mass per month in space,” said Dr Siew. The absence of gravity means astronauts don’t use their muscles as much, leading to atrophy. Their bones, no longer bearing weight, weaken over time. To combat these effects, astronauts undergo months of physical therapy after returning, helping them regain their strength and bone density.

Also read: Dizziness, gravity sickness, weightless tongue, baby feet: What astronauts face back on earth

Impact on heart health

Space travel also affects the heart. “The heart can shrink over time due to reduced workload in microgravity,” Dr Siew explained.

Astronauts follow strict exercise routines in space to maintain cardiovascular health but even so, their hearts must readjust to working against gravity after returning to Earth.

Disorientation and balance issues

Space travel disrupts the vestibular system, which controls balance. “Their inner ear is not used to gravity, so astronauts experience balance issues when they return,” said Dr Siew. This disorientation can last for weeks. Some astronauts have even been known to forget that gravity exists and accidentally drop objects they assume will float.

The transition back to Earth also affects the nervous system. Astronauts experience sensory changes and may struggle with depth perception and spatial awareness. These effects truly highlight how our connection to gravity is so deeply ingrained in us.

What does re-entry feel like?

Dr Siew likens the descent to “the most intense rollercoaster ever”.

Astronauts experience extreme turbulence, high g-forces, and temperature changes. Their bodies undergo fluid shifts, and they must train to withstand these forces.

Watch: Sunita Williams returns: Science behind astronaut recovery, what India can learn

Effects of extended space travel

Astronauts who spend long durations in space face even greater challenges. “Scott Kelly, who spent a year in space, participated in a twin study with his brother Mark, revealing major biological changes,” shared Dr Siew.

DNA and immune system changes

One surprising finding has been the alteration of telomeres—the protective caps at the ends of chromosomes. “Telomeres actually got longer in space, which was unexpected,” Dr Siew noted. Scientists previously thought space mimicked accelerated aging, but this discovery challenges that assumption.

The immune system also weakens in space. “Space seems to dampen immune response, making astronauts more susceptible to infections,” Dr Siew explained.

Reactivated viruses like herpes are common among astronauts, and changes in gut bacteria have been observed, including the development of drug-resistant microbes.

Vision problems, kidney stone risk

Another lesser-known issue is space-acquired neuro-ocular syndrome (SANS). “Fluid shifts cause pressure build-up in the eyes, which can change their shape,” Dr Siew said. Many astronauts return with worsened vision, often requiring glasses despite having perfect eyesight before their mission.

Astronauts are also at a higher risk of kidney stones. “They have a seven to 14 times greater risk of developing kidney stones in space, and this risk remains high for a year after returning,” Dr Siew explained.

Radiation exposure is another concern, as astronauts are bombarded with cosmic rays that can damage cells and increase cancer risk.

Applying space medicine on Earth

Space research has valuable applications for everyday medicine. “Space travel mirrors many conditions we see on Earth, such as osteoporosis, muscle degeneration, and cardiovascular disease,” Dr Siew explained. Insights from space medicine can help improve treatments for bedridden patients, the elderly, and cancer patients undergoing radiation therapy.

Studying bone loss in astronauts could lead to better treatments for osteoporosis. Similarly, space research on muscle atrophy helps in developing therapies for people suffering from muscle-wasting diseases or age-related frailty.

Kidney damage

Research on kidney damage in space could help to protect cancer patients undergoing radiation therapy.

“If we can develop drugs to prevent kidney damage in astronauts, we might be able to use them for patients receiving radiotherapy,” Dr Siew said.

Recovery programme on Earth

After returning to Earth, astronauts go through a structured recovery programme. “The first priority is addressing immediate health risks like blood flow issues and fractures due to weakened bones,” Dr Siew said.

The recovery process includes cardiovascular exercises, strength training, and a tailored nutrition plan. “For the first 45 days, they focus on rebuilding muscle and bone mass,” Dr Siew explained. However, not all effects are reversible.

“Bone density loss is almost impossible to regain fully after long-duration spaceflight.”

Gender differences

While men and women generally undergo similar recovery processes, research suggests that women may have a slight advantage. “Women appear to be more resistant to immune system changes in space,” Dr Siew noted.

Ongoing research aims to determine how spaceflight affects men and women differently, which could lead to personalised rehabilitation programmes.

Future of space medicine

With upcoming missions to Mars and beyond, understanding space medicine has become more crucial than ever.

Space agencies like NASA and ISRO are focusing on improving astronaut health and reducing long-term risks.

Dr Siew emphasised that these studies not only prepare humans for deep-space travel but also offer groundbreaking medical advancements for people on Earth.

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