The Space Growth Spurt: Why Astronauts Get Taller in Microgravity
That is absolutely true! If you spent a few months on the International Space Station (ISS), you would likely return to Earth about 2 inches (5 cm) taller than when you left.
While gaining a couple of inches of height sounds like a “space superpower,” the reason behind it is actually quite simple—and it’s more about your spine stretching than your body actually growing.
Why It Happens: The Gravity “Accordion”
On Earth, gravity is constantly pulling you down, compressing your spine. Between each of your vertebrae (the bones in your back) is a soft, gel-like pad called an intervertebral disc. These discs act as shock absorbers.
In the microgravity environment of space:
- Decompression: Without the weight of gravity pushing down on you, the pressure on those discs is released.
- Expansion: The discs are able to expand and absorb more fluid, causing the space between your vertebrae to widen.
- Straightening: The natural “S” curve of your spine also tends to flatten out slightly, adding even more to your total height.
How Much Do You “Grow”?
Most astronauts grow by about 3% of their original height. For someone who is 6 feet tall, that’s almost exactly 2 inches.
A famous example is NASA astronaut Scott Kelly, who spent nearly a year in space. When he returned, he was two inches taller than his identical twin brother, Mark, who had stayed on Earth!
The Catch: It’s Not Permanent
Unfortunately for anyone hoping for a permanent height boost, this effect is temporary.
- The Return: As soon as an astronaut returns to Earth, gravity immediately begins “squishing” the spine back down.
- The Timeline: Most astronauts return to their original height within a few days to a few weeks.
- The Growing Pains: This process isn’t always comfortable. Many astronauts report significant back pain as their spine re-compresses and their muscles (which may have weakened in space) struggle to support their weight again.
Fun Fact: You Grow Every Night!
You don’t actually need a rocket ship to experience this. Because you lie flat when you sleep, gravity isn’t compressing your spine vertically. This means you are actually about half an inch taller when you wake up in the morning than when you go to bed at night!
n summary, while the idea of “growing” in space sounds like a dream for anyone wanting a few extra inches, it is really a testament to how much Earth’s gravity shapes our daily lives.
Final Takeaways
- A “Spinal Vacation”: Height gain in space is simply your spine decompressing and your intervertebral discs expanding without the constant weight of gravity.
- Earth-Bound Reality: Because this change is structural and not biological (you aren’t growing new bone), gravity will reclaim those inches almost as soon as you land.
- The Price of Height: The extra height often comes with back pain and muscle stiffness, proving that our bodies are finely tuned—and specifically designed—to live under $1\text{g}$ of pressure.
This “stretch” is just one of the many ways the human body adapts to the final frontier. It serves as a reminder that when we send humans into the stars, we aren’t just sending minds and machines; we are sending biological systems that evolved for a very specific environment here on the ground.