NASA found astronauts can become up to 3% taller in space; their spines lengthen without Earth’s gravity, then compress again after landing

Up in the air somewhere above your head, there's an astronaut aboard the International Space Station who's taller than when he or she first launched into orbit. They're not just standing a bit straighter. They are actually taller, up to 3% of their height in fact, as described in a NASA study summary “Risk of Spaceflight-Induced Bone Changes,” which attributes the change to the spine straightening out and elongating in microgravity, not to any actual growth of bone. If that astronaut is six feet tall, that means they've gained almost two inches in height without having to do anything about it. That sounds like a total glow-up. Except it isn't.

So how does a grown adult just get taller?

On planet Earth, gravity is slowly compressing you every minute of the day. The gravitational force acts upon your spine and squeezes the water-containing discs present between the vertebrae, thus flattening out your spine's natural curve. That is why everyone is technically a few millimeters shorter at night than at daybreak. Take gravity out of the picture, and that daily compression stops happening: the spine straightens out and the fluid-filled discs between the vertebrae are free to expand, so the whole spinal column lengthens. The increase in height is not growth as such; there is no increase in bone length.


The glow-up is temporary

All that apparent additional height is lost in a matter of days to weeks after returning, as gravity gets back to work, compressing the spine. Yet, the astronaut does not simply shrink back to normal and get back to living their life. As per a 2016 study titled “Lumbar Spine Paraspinal Muscle and Intervertebral Disc Height Changes in Astronauts After Long-Duration Spaceflight on the International Space Station,” published in the journal Spine, scientists who used an MRI to scan astronauts both before and after a six-month mission aboard the ISS noted visible muscle atrophy of their lower-back muscles and failure of those muscles to recover even several weeks post-mission. Translation: the muscles that should support the spine just take a vacation when you are weightless, and they don't come back right away.

This is because the spine that has been elongated, unsupported, and loaded in an unnatural way for months does not really like coming back under gravity. This was stated in a 2010 research paper titled “Risk of herniated nucleus pulposus among U.S. astronauts,” in the journal Aviation, Space, and Environmental Medicine. Astronauts have a significantly increased chance of herniated disc shortly after they return compared to those who did not fly anywhere. This is an injury that often requires several months of therapy.

Why should this matter

The scenario is too familiar because there's always something about the body looking good on the outside while something is silently falling apart inside, and the consequences become clear once the thrill of the experience is over. No matter how long and hard astronauts are prepared for space flight, they cannot completely avoid the effects. It is a good reminder that temporary relief from pressure and actual healing are two different things.

However, it is important to be aware of what really happens when one decides to try space tourism. As flights become longer and longer and non-astronauts join the space program, the phrase "you might come back a couple inches taller" will start being repeated at social gatherings. And it is true. But it is just one part of the picture, which is quite visible. Muscles lost and discs strained are not as easy to overlook. NASA takes this fact seriously and uses it as the basis of its countermeasures; astronauts work according to strict programs aimed at protecting the spine.