How astronauts come back from space as ‘different people’ has been explained

  • Astronauts including Mark Vande Hei are said to come back from space ‘different people’
  • The Translational Research Institute for Space Health has compiled research on the effects of space travel
  • From muscle and eye health to cognitive function and the effects of radiation – here’s what we know

Published on Jan 09, 2024 at 9:33 PM (UTC+4)
by Amelia Jean Hershman-Jones

Last updated on Jan 11, 2024 at 1:08 PM (UTC+4)
Edited by Alessandro Renesis

How astronauts come back from space as ‘different people’ has been explained

Going into space is no walk in the park – in fact it’s said that astronauts come back from space as ‘different people’.

A space walk is certainly no cake walk, according to the the Translational Research Institute for Space Health (TRISH).

With that in mind, TRISH has collated research projects and studies to unpick the challenges humans face during space exploration.

READ MORE! Spine-tingling new NASA image shows ‘ghostly cosmic hand’ 16,000 light-years from Earth

It’s something we’ve seen a lot of recently with NASA sending an identical twin to space for a year to see how he’d change.

NASA astronaut, Mark Vande Hei, came back down to Earth after spending a record-breaking 355 consecutive days in space on board the International Space Station (ISS).

And he’s not the same person he was before.

What’s more, NASA astronaut Frank Rubio’s body changed after more than a year in space.

Scientists want to understand and mitigate these changes ahead of NASA’s Artemis missions and, eventually, crewed missions to Mars.


The bones of the lower body do less work minus the oppressive gravity of Earth.

The pressure is off the spine, hips and legs.

While it might seem like this could be a plus, this results in lowered bone density and subsequent mineral content elsewhere in the body.

This can lead to problems including urinary calcium and renal stones.


While you might have experienced this to a lesser extent during a gym hiatus – with muscle it’s a ‘use-it-or-lose-it’ situation.

Less gravity means astronauts use their muscles less in space and a decrease in muscle mass, strength and endurance follows.

Using the lower-body less because you’re not walking, standing or even sitting in the same way, which can eventually lead to weakened, atrophied muscles.

While we know diet is a focus onboard ISS, astronauts also adhere to a strict exercise regime to make sure those small steps on the moon, Mars – or back here on Earth – are as strong as possible.


Microgravity takes some getting used to.

On Earth, our brain uses a complex and overlapping network of neural circuits that allow us to maintain balance, stabilize vision, and orient location and direction.

It does this by interpreting information from the eyes, inner ear vestibular organs, and the deep senses from muscles and joints.

Without gravity to ground us, however, this information the body receives is altered with sensorimotor function and postural stability lacking.

During the early days of a space mission, astronauts often experience disorientation, space motion sickness, and a loss of sense of direction.

This, in turn, makes daily life in space difficult and emergency situations more dangerous.

And these issues can continue back on terra firma, with issues standing, stabilizing their gaze, walking, and turning.

Returning astronauts are often placed in a chair for safety when they first touch down on Earth.


During long-duration missions the eyes can struggle.

Changes include increased globe flattening, optic disc edema, and vision changes.

Space-Associate Neuro-ocular Syndrome (SANS), causes swelling in the back of the eye.

It’s one of the most significant risks.

Before embarking on a three-year mission to Mars, this serious issue needs looking into.


The environment of space can decrease astronaut’s blood volume, orthostatic tolerance, and aerobic capacity.

Conversely, they can also experience increased arrhythmias.

Like other musculature, the cardiovascular system doesn’t require as much work from the heart in microgravity.

This can lead to a gradual deconditioning and decrease in heart size that overextends back on Earth.

It’s thought that space radiation could also affect endothelial cells that sit in blood-vessel lining.

There’s a risk that this could spark or speed up coronary heart disease.  

Cognitive function 

Spaceflight agencies and companies need their astronauts to carry out their mission effectively during their time in space.

Confinement in a small space with others, high work demands, team and crew issues, in addition to the loss of the 24-hour day/light cycle can accumulate.

The result can be fatigue, stress and decreased cognitive function.

Ultimately this may jeopardize a mission and the safety of those in space.

Gastrointestinal system  

Another muscly part of the body, the gastrointestinal system, also feels the effects of a loss of gravity.

Minus the gravity that helps move food through the GI tract and the usual method of going to the bathroom, the intestinal system experiences decreased motility.  

Environmental Effects 

Being constantly aboard a capsule or space station can also have an effect on the body;

Noise exposure can cause hearing loss.

Plus, while it might sound relaxing, being off your feet for such a long time can have its issues.

These include callouses on the top of feet from footholds, softness from disuse and a lack of sensitivity to pressure variations.

A lowered immune system and recycled air can also lead to skin irritation from microbial growth.

Space radiation 

Lucky us: while on Earth, its protective atmosphere shields us from harmful space radiation.

Beyond Low Earth Orbit (LEO), space radiation can pose a significant risk when astronauts are exposed to 100 times the levels of humans on Earth.

According to NASA, that’s equivalent to 150 to 6,000 chest x-rays.

It can lead to radiation sickness, central nervous system effects, degenerative diseases, and an increased lifetime risk of cancer.

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Amelia Jean Hershman-Jones

London-based Amelia cut her journalistic teeth covering all things lifestyle, wellness and luxury in the UK capital. Fast-forward a decade and the experienced content creator and editor has put pen to paper for glossy magazines, busy newsrooms and coveted brands. When her OOO is on you can find her spending quality time with her young family, in the gym or exploring the city she loves.