Astronauts get taller in space, but....

March 3, 2016 4:20 AM

Astronaut Scott Kelly came back to Earth this week after almost a full year on the ISS. Reportedly, he has gained two inches in height. He's not the only one this has happened to, of course: it's a known effect of living in zero gravity. But will he keep that additional height?

Okay, gravity squishes us down, and zero gravity allows the bones of the spine to 'float' more, because of the reduced downward pressure. Allowing for shrinkage due to old age and things like that, will he remain two inches taller, will he eventually return to his pre-flight height (and how long would that take?), or will he end up somewhere inbetween his pre-flight and post-flight heights?

posted by easily confused to Health & Fitness (5 answers total)

My bet: He will lose the height, because his spine will readjust to Earth gravity and because he certainly has spaceflight osteopenia, which will eventually cause at least some vertebral compression, and that, in turn will result in height loss independent of the muscular reset.
Fun fact: we all gain a little height every night and lose it over the course of the day because of postural changes and muscle fatigue.
posted by gingerest at 4:49 AM on March 3, 2016 [11 favorites]

Best answer: I'm pretty sure he'll lose most if not all of that height gain, and probably pretty quickly, provided he's able to stand and sit comfortably in normal gravity.

It's true that people get taller overnight as they sleep. Almost all of that normal increase in height comes from the intervertebral disks that reside between the vertebrae of the spine. The IVDs have a jelly-like core that contains a lot of water. During the day, the IVDs are compressed by the body's weight, and slowly lose water. Provided you sleep in a horizontal position—as most do—and you are well hydrated, the IVDs slowly rehydrate overnight, causing them to gain some thickness. You get taller.

I imagine a year in microgravity would make for nice, plump IVDs. Maybe Scott Kelley has staved off for a year the normal disk degeneration we all suffer, and if so, lucky him. Then again, maybe his IVDs are very weak-walled now, having not been challenged by weight-bearing for such a long time. This is one of the many interesting things we might learn from comparing him to his identical twin. Here's hoping they're both getting full-body MRIs as we speak!
posted by cyclopticgaze at 5:47 AM on March 3, 2016 [1 favorite]

Best answer: My bet: He will lose the height,

But until that happens be assured he'll have no end of fun when meeting up with his twin to exclaim: "Hi there little brother".
posted by sammyo at 5:49 AM on March 3, 2016 [14 favorites]

"Once the astronauts return to Earth, their height returns to normal after a few months." - From Strange But True: Astronauts Get Taller in Space
posted by Mr.Know-it-some at 7:14 AM on March 3, 2016 [2 favorites]

The IVDs have a jelly-like core that contains a lot of water. During the day, the IVDs are compressed by the body's weight, and slowly lose water...Then again, maybe his IVDs are very weak-walled now, having not been challenged by weight-bearing for such a long time.

I would actually guess that the walls are stronger due (or at least not weaker) to increased pressure within the IVDs. That's similar to the issue with eyesight damage in microgravity. "That increased pressure of cerebrospinal fluid, which surrounds the brain, works its way down the sheath of the optic nerve and pushes on the back of the eyeball," Shelhamer said during his FISO presentation.
posted by Beti at 9:06 AM on March 3, 2016