Your Body
Do astronauts get taller in space?
The short answer
Yes. NASA reports that crew members grow up to three percent taller during long missions on the International Space Station, about five centimetres for a six-foot person. Without gravity squashing the spine, the discs between the vertebrae expand. Height returns to normal after coming home.
Your spine is a stack of bones with soft, springy discs between them. All day, gravity presses the stack down. In orbit, nothing presses, so the discs plump up and the stack gets longer. NASA has measured the effect at up to three percent of a person's height, which for a tall astronaut is roughly the width of a hand.
You do a tiny version of this every night. Lying flat takes the load off the discs, which is why most people are a little taller first thing in the morning than they are at bedtime. Space just makes the night last six months.
NASA studied the stretch with an ultrasound scanner on the station, with astronauts scanning each other's backs guided by doctors on the ground. The extra height is not a bonus. Longer spines with weaker supporting muscles mean more back pain and a higher risk of slipped discs after landing, and the gain disappears within months of returning to gravity.